As the oceans gradually become warmer and more acidified, an increasing number of studies test the effects of climate change on marine organisms. As most climate change experiments have studied effects of single climate variables on single species, more and more researchers ask themselves how this lack of realism affects our ability to accurately assess and predict effects of climate change (Wernberg et al. 2012). Interestingly, theory and a growing body of studies suggests that different climate variables can strongly interact (Kroeker et al. 2013), that climate effects can change with presence/absence of strong consumers (Alsterberg et al. 2013), and that effects on communities are more informative than those on single species, as they allow experimenters to assess what traits that makes organisms sensitive or resistant (Berg et al. 2010). In our new paper “Community-level effects of rapid experimental warming and consumer loss outweigh effects of rapid ocean acidification” we found that warming and simulated consumer loss in seagrass mesocosms both increased macrofauna diversity, largely by favoring epifaunal organisms with fast population growth and poor defenses against predators.

These results corroborate theory, and exemplify how trait- and life-history based approaches can be used to in more detail understand – and potentially predict – effects of climate change. Meanwhile, simulated ocean acidification (pH 7.75 vs. 8.10) had no detectable short-term effects on any of the investigated variables, including organisms with calcium-carbonate shell. While this lack of effect may be partly explained by the short duration of our experiment and/or the relatively crude endpoints, seagrass-associated macrofauna routinely experience diurnal pH variability that exceed predicted changes in mean pH over the coming century (Saderne et al. 2013). Consequently, by living in a variable pH these organisms could be relatively resilient to ocean acidification (see e.g. Frieder et al. 2014). In summary, it seems that at least in the short term, rapid warming and changes in consumer populations are likely to have considerably stronger effects than ocean acidification on macrofauna communities in shallow vegetated ecosystems.

References cited above:

Alsterberg, C., Eklöf, J. S., Gamfeldt, L., Havenhand, J. and Sundbäck, K. 2013. Consumers mediate the effects of experimental ocean acidification and warming on primary producers. – PNAS 110: 8603-8608.

Berg, M. P., Kiers, E. T., Driessen, G., van der Heijden, M., Kooi, B. W., Kuenen, F., Liefting, M., Verhoef, H. A. and Ellers, J. 2010. Adapt or disperse: understanding species persistence in a changing world. – Global Change Biol 16: 587-598.

Frieder, C. A., Gonzalez, J. P., Bockmon, E. E., Navarro, M. O. and Levin, L. A. 2014. Can variable pH and low oxygen moderate ocean acidification outcomes for mussel larvae? – 20: 754-764.

Kroeker, K. J., Kordas, R. L., Crim, R., Hendriks, I. E., Ramajo, L., Singh, G. S., Duarte, C. M. and Gattuso, J.-P. 2013. Impacts of ocean acidification on marine organisms: quantifying sensitivities and interaction with warming. – Glob. Change Biol. 19: 1884-1896.

Saderne, V., Fietzek, P. and Herman, P. M. J. 2013. Extreme Variations of pCO₂ and pH in a Macrophyte Meadow of the Baltic Sea in Summer: Evidence of the Effect of Photosynthesis and Local Upwelling. – PloS ONE 8: e62689.

Wernberg, T., Smale, D. A. and Thomsen, M. S. 2012. A decade of climate change experiments on marine organisms: procedures, patterns and problems. – Glob. Change Biol. 18: 1491-1498.

 

As the oceans gradually become warmer and more acidified, an increasing number of studies test the effects of climate change on marine organisms. As most climate change experiments have studied effects of single climate variables on single species, more and more researchers ask themselves how this lack of realism affects our ability to accurately assess and predict effects of climate change (Wernberg et al. 2012). Interestingly, theory and a growing body of studies suggests that different climate variables can strongly interact (Kroeker et al. 2013), that climate effects can change with presence/absence of strong consumers (Alsterberg et al. 2013), and that effects on communities are more informative than those on single species, as they allow experimenters to assess what traits that makes organisms sensitive or resistant (Berg et al. 2010). In our new paper “Community-level effects of rapid experimental warming and consumer loss outweigh effects of rapid ocean acidification“ we found that warming and simulated consumer loss in seagrass mesocosms both increased macrofauna diversity, largely by favoring epifaunal organisms with fast population growth and poor defenses against predators.

These results corroborate theory, and exemplify how trait- and life-history based approaches can be used to in more detail understand – and potentially predict – effects of climate change. Meanwhile, simulated ocean acidification (pH 7.75 vs. 8.10) had no detectable short-term effects on any of the investigated variables, including organisms with calcium-carbonate shell. While this lack of effect may be partly explained by the short duration of our experiment and/or the relatively crude endpoints, seagrass-associated macrofauna routinely experience diurnal pH variability that exceed predicted changes in mean pH over the coming century (Saderne et al. 2013). Consequently, by living in a variable pH these organisms could be relatively resilient to ocean acidification (see e.g. Frieder et al. 2014). In summary, it seems that at least in the short term, rapid warming and changes in consumer populations are likely to have considerably stronger effects than ocean acidification on macrofauna communities in shallow vegetated ecosystems.

 

References cited above:

Alsterberg, C., Eklöf, J. S., Gamfeldt, L., Havenhand, J. and Sundbäck, K. 2013. Consumers mediate the effects of experimental ocean acidification and warming on primary producers. – PNAS 110: 8603-8608.

Berg, M. P., Kiers, E. T., Driessen, G., van der Heijden, M., Kooi, B. W., Kuenen, F., Liefting, M., Verhoef, H. A. and Ellers, J. 2010. Adapt or disperse: understanding species persistence in a changing world. – Global Change Biol 16: 587-598.

Frieder, C. A., Gonzalez, J. P., Bockmon, E. E., Navarro, M. O. and Levin, L. A. 2014. Can variable pH and low oxygen moderate ocean acidification outcomes for mussel larvae? – 20: 754-764.

Kroeker, K. J., Kordas, R. L., Crim, R., Hendriks, I. E., Ramajo, L., Singh, G. S., Duarte, C. M. and Gattuso, J.-P. 2013. Impacts of ocean acidification on marine organisms: quantifying sensitivities and interaction with warming. – Glob. Change Biol. 19: 1884-1896.

Saderne, V., Fietzek, P. and Herman, P. M. J. 2013. Extreme Variations of pCO₂ and pH in a Macrophyte Meadow of the Baltic Sea in Summer: Evidence of the Effect of Photosynthesis and Local Upwelling. – PloS ONE 8: e62689.

Wernberg, T., Smale, D. A. and Thomsen, M. S. 2012. A decade of climate change experiments on marine organisms: procedures, patterns and problems. – Glob. Change Biol. 18: 1491-1498.

 

Understanding how changes in the climate affect biological communities is essential in predicting the future size and composition of populations. However, accurate predictions pose a difficult challenge for researchers. For the majority of animal species it is not feasible or ethical to conduct experiments into how these populations will respond to a changing climate. To enable us to gain an insight into potential futures of a population under climatic change, we use a computational model. Specifically, we use an integral projection model to investigate how changes in the North Atlantic Oscillation will influence the body weight and population size of a population of Soay sheep. The North Atlantic Oscillation is a large scale weather pattern of temperature differences across the Atlantic Ocean, which alters the local weather patterns in the North Atlantic region. We used published predictions of the future values of the North Atlantic Oscillation for the 21^st Century. By doing this we are able to project the response of the study population to climate change based on our current best projections of the future climate.

Our model results, presented in the Early View paper “Analysis of phenotypic change in relation to climatic drivers in a population of Soay sheep”,  suggest that a continued positive trend in the North Atlantic Oscillation (positive pressure difference between Iceland and the Azores), as predicted by the majority of models, will be accompanied by a decrease in the population size of the Soay sheep and an increase in mean body weight. These changes are likely caused by a loss of smaller individuals from the population due to higher mortality in the adverse winters (mild but wet and windy) associated with the positive North Atlantic Oscillation.

Using an integral projection model as we have in this study gives us a glimpse into the potential future of populations where experimentation is difficult, and can improve our understanding of how populations will respond to changing climatic conditions. Using published climate predictions within our model also allows such studies to be placed in the realm of current climate research and (importantly) our projections can be updated as new climate predictions are released.

This is our first collaboration study between a population geneticist, Hideki Innan, and a field-based tropical ecologist, me, Yayoi Takeuchi.
I have been long wondering why Hubbell’s neutral model fitted so well to tropical forest communities because my impression of the tropical forest was the opposite. When I was doing my postdoctoral work in Hideki’s lab, he got interested in this issue because Hubbell’s model is based on the theory of population genetics. As such we started working together on this topic, and I found that population genetics holds sophisticated and well-established theories and methodologies, which could be well applied to community ecology. We believe that incorporating those techniques will provide breakthrough insights to elucidate mechanisms shaping complex natural communities.

A species-rich tropical rain forest in Lambir Hills National Park in Sarawak, Malaysia. Photo by Yayoi Takeuchi

The study “Evaluating the performance of neutrality tests of a local community using a niche-structured simulation model” summarized:

Is your favorite local community really neutral? —- It might be “No”! Here, we found that two common methods to test Hubbell’s neutral model were not robust enough to reject neutrality.
Hubbell’s neutral model provides a good fit to the data from wide range of natural communities including tropical forests and coral reefs. There are two parameters in his model that are usually unknown and commonly estimated from the data to be tested. Two common methods to test Hubbell’s neutral model, the SAD-fitting approach and re-sampling approach, use these estimated parameters. To examine the performance of these tests, we developed a simple niche model which incorporates stochastic demography, and these two tests were applied to a simulated non-neutral data with niche-structured community. Our results suggested that these tests had relatively poor power to reject neutrality, simply due to overfitting of the neutral model with unrealistic estimated parameters. We also discussed how we could improve the performance in this paper.

The introduction of a new species to an ecological community can initiate a chain of events that results in a significant change to the community’s composition. For instance, the introduction of a pollinator species can facilitate the colonization of new plants that rely on the new pollinator for reproduction. Conversely, a pollinator species may drive down the population levels of certain species—e.g., if it aggressively robs a plant of its nectar without pollinating it.

How do communities respond to these invasions, and what lessons can be learned about the underlying properties of ecological communities in response to such invasions? In “Plant-pollinator community network response to species invasions depends on both invader and community characteristics,” the authors investigate the relationships between invasive species and community characteristics in shaping a plant-pollinator community’s response to an invasion.

Monarch butterfly (Danaus plexippus) on invasive plumeless thistle (Carduus acanthoides). Photo credit: Laura Russo

The study makes use of a computational model that was originally used to investigate the process by which stable plant-pollinator communities form. The use of such models is attractive for two main reasons. First, a model that recapitulates real-world behavior offers insight into the mechanisms that operate in nature; second, computational models allow rapid and widespread exploration that would be time-consuming, costly, and in some cases impractical to perform in nature. As such, computational models are well-positioned to speed up the process of scientific discovery by providing novel and informative predictions and insights into the properties of the systems being modeled.

The model itself is used to generate simulated plant-pollinator communities with properties drawn from the empirical literature. Interactions may be true mutualisms (beneficial to both species) or detrimental to one species and beneficial to another (e.g., insects that visit flowers for nectar without pollinating the plant and plants that trick pollinators without providing them with nectar rewards). Colonization or maintenance of a species in the community is possible if its beneficial interactions outweigh its detrimental interactions; otherwise, the species goes extinct.

The model predicts that invasive species with properties that are very different from the native species in the region (e.g., supergeneralists that benefit the species with which they interact) are more likely to drive significant changes in the number of species colonizing the community. When an invasive species increases the species richness of the invaded community, there is a corresponding increase in the community’s nestedness and a decrease in the community’s connectance. Nestedness is a measure that accounts for the tendency of the community to be composed of (1) generalist species that interact with many species and (2) specialist species that interact with a subset of generalists. Connectance is the number of observed interactions relative to the number of possible interactions. This predicted divergence in nestedness and connectance is in agreement

with recent empirical work, and stands in contrast to the correlation of these two measures when considering the process by which communities stabilize.

This finding is relevant to the active discussion among researchers concerning the relationship between nestedness and connectance. By investigating the differing behavior of these properties in the context of species invasion, this paper supports the argument that nestedness and connectance are complementary properties that provide a more accurate picture of a community together than either measure provides alone. These findings are most strongly supported in the context of invaders that increase the number of species colonizing the community. As these invaders tend to participate in many species-species interactions, this paper also highlights the important role of generalist species in shaping the structure and dynamics of ecological communities.

Despite the increasing use of Species Distribution Models (SDM) for predicting current or future animal distribution, only a few studies have linked the gradient of habitat suitability to demographic parameters.

Species Distribution Models are a niche modelling framework based on a statistical approach linking spatial data on the presence/absence of species to predictive environmental variables. Because they do not account for demographic and ecological processes that may constrain responses to environmental factors at a population level, the projections of SDM cannot be used directly to predict the associated extinction risk. In this context, approaches accounting for mechanistic processes directly linked with extinction across distribution ranges are considered as promising steps to better understand and predict the response of species to environmental change. While such approaches can improve the reliability of models, empirical works are essential to further develop our understanding of processes underlying distribution patterns and potentially develop better SDM that could integrate factors driving species distribution and persistence. Moreover, the adequacy of projections with demographic parameters is a critical issue when they have to be applied for conservation planning.

In our study “Evidence of a link between demographic rates and species habitat suitability from post release movements in a reinforced bird population” just published in Oikos, we tested whether the spatial variation in habitat suitability along the individual movement path is related to survival.

Radio-tracking of North African Houbara Bustard in Eastern Morocco

We used an extensive tracking data collected from captive-born individuals translocated to reinforce the wild populations of Houbara bustard (Chlamydotis undulata undulata). This translocation program provides an ideal study framework including information on the spatial distribution of wild-born individuals and intensive individual-based monitoring of captive-bred released individuals.

We first modelled and mapped the habitat suitability from presence data of wild individuals using niche models in a consensus framework (BIOMOD platform). We further analysed survival of 957 released individuals using capture-recapture modelling and its links to habitat suitability, as the trend in suitability from the release sites along movements.

North African Houbara Bustard (Chlamydotis undulata undulata)

We found that the survival of released individuals was related to changes in habitat suitability along their movements. For instance, individuals which moved to sites of lower habitat suitability than their release sites have lower survival probabilities than the others, independently of the habitat suitability of the release sites and daily movement rate. Interestingly, the most positive changes in habitat suitability were not characterized by highest survival probabilities, likely due to density-dependant processes.

We provide an empirical support of the relationship between habitat suitability and survival, a major fitness component. These results illustrate the relevance of linking demographic processes with Species Distribution models, but also underline the importance of other mechanisms acting on demographic parameters and possibly mitigating such relationship (social organisation, density dependence).

The authors through Anne-Christine Monnet

 

Everyone who likes to spend some time in nature, or who has trees at home, knows that several animals love to feed on fruits. Figs, tomatoes, peppers, guavas, mangos, bananas, and many other delicacies are harvested by frugivores that range from tiny bats to huge elephants.

Those animals render the plants a service known as seed dispersal: in other words, they carry their seeds away and so increase the chances of their offspring surviving attacks by natural enemies, establishing, and colonizing new sites. This myriad of interactions forms a tangled web of frugivores and fruits, which is vital to maintain and regenerate forests and other natural ecosystems. Some frugivores seem to be more important than others to keep those webs functioning. In our study “Keystone species in seed dispersal networks are mainly determined by dietary specialization”, focused on bats and birds, the main groups of seed dispersers in the Neotropics, we found out that, even though animals with other kinds of primary diets participate in seed dispersal networks, specialized frugivores are the keystones of those systems and hold them together. This finding may help plan for the conservation and restoration of seed dispersal in degraded areas, and also provide insights on how to accelerate the regeneration of tropical rainforests and savannas.

Marco A.R. Mello and co-authors

Experimental warming is an effective approach to determine the effect of increasing temperature on ecological processes, with few confounding factors (e.g., other variables that covary spatially and temporally with temperature). Therefore, a number of field experiments have been initiated worldwide to study the effects of simulated global warming. A wide range of techniques (e.g., greenhouses, open-top chambers, and electric infrared heaters) have been developed to experimentally warm a variety of small plants, including those of the tundra, grasslands, and sapling trees. Within forests, most insect species diversity and plant-insect interactions are concentrated in the canopy of mature trees, rather than in the understory, because of higher plant productivity. However, few studies have examined the responses of mature trees to experimental warming in natural forests.

In the paper “Different initial responses of the canopy herbivory rate in mature oak trees to experimental soil and branch warming in a soil-freezing area”, we report the initial 3-year (2007–2009) results of an experimental warming of mature Quercus crispula (18–20 m in height), a late-successional tree species. Five mature Q. crispula trees whose canopy was accessible by a gondola hanging from a construction crane were selected (Photo1). To better understand the mechanism by which global warming affects plant-insect interactions in the canopy of mature oak trees, field experiments must warm aboveground and belowground regions separately. Thus, we experimentally increased the temperature of the surrounding soil and canopy branches of mature oak trees by approximately 5°C using electric heating cables (Photo 2 and 3).

Our warming experiment clearly demonstrates that plant-insect interactions in the canopy responded differently to soil and branch warming of mature oak trees. Soil warming in a mature cool-temperate forest with a freeze-thaw cycle decreased the nutritional quality of leaves and the rate of herbivory in the canopy, whereas branch warming had no effect on canopy leaf traits or the herbivory rate. The magnitude of the indirect (plant-mediated) effects of belowground temperature elevation on canopy herbivory was gradually enhanced during the initial 3 years of the study. These results suggest that belowground temperature elevation due to global warming in a soil freezing area is an important driving force of plant-insect interactions in the canopy. For a better understanding of the mechanism by which global warming affects plant-insect interactions in mature cool-temperate forests, this warming experiment should be continued using mature oak trees because indirect effects of temperature are likely more pronounced in the long- than in the short-term.

Masahiro Nakamura and co-workers

Elevational gradients have become important tools for assessing the effects of temperature changes on vegetation properties, because these gradients enable temperature effects to be considered over larger spatial and temporal scales than is possible through conventional experiments. During the summer of 2012, we collected soils along an elevational gradient on Mount Suorooaivi near Abisko, Sweden for two growth chamber experiments to determine the effects of temperature, soil origin (proxy for soil legacy) and vegetation type on the growth responses of two grass species. The results are published in the Oikos paper “Plant growth response to direct and indirect temperature effects varies by vegetation type and elevation in a subarctic tundra”. 

Soils were collected at each of three elevations from each of two vegetation types, specifically heath, dominated by dwarf shrubs, and meadow, dominated by graminoids and herbs. Plants responded to both the direct effect of temperature and its indirect effect via soil legacies, and that direct and indirect effects were largely decoupled. Vegetation type was a major driver of plant response; responses to soils from increasing elevation were stronger and seedlings showed a more linear decline in biomass when grown in meadow as opposed to heath soils.

The effect of soil biota on plant growth was independent of elevation, with a positive influence across all elevations regardless of soil origin for meadow soils but not for heath soils. Collectively, the responses of plant growth to soil legacy effects of temperature across the elevational gradient were driven primarily by soil abiotic, and not biotic, factors. These findings demonstrate vegetation type is a strong determinant of how temperature variation across elevational gradients impacts on plant growth, and highlight the need for investigating both direct and indirect effects of temperature on plant responses to future climate change.

 

Jonathan de Long and co-workers

Biotic interactions play a central role in determining species distribution and abundance. Indeed, some organisms can have particularly strong effects on the distribution of other species because they act as keystone species or ecosystem engineers whose effects cascade to other trophic levels – beavers are one well-known example of this. In coffee agroecosystems in Southern Mexico we studied how a keystone species, the dominant arboreal ant A. sericeasur, influences the distribution and abundance of Pocobletus sp. nova, tiny spiders that spin their webs in coffee plants (Fig. 1 and Fig. 2). The results are now published Early View in Oikos in the paper “A positive association between ants and spiders and potential mechanisms driving the pattern”

 

Figure 1. Pocobletus sp. nova on a coffee bush. Notice the hammock web; the white little balls are Pocobletus ovisacs

 

 

Figure 2. Close up of a female of Pocobletus sp. and its spiderlings. Ovisacs in the background.

 

The first thing that we noticed when sampling spiders in coffee plants was that Pocobletus spiders tended to be very abundant in the presence of A. sericeasur. So we asked ourselves, why are these tiny spiders associated with these ants? To what extent do the dominant A. sericeasur ants influence the spatial distribution of Pocobletus?

 

In the summer of 2010, we set up four plots around shade trees that had A. sericeasur nests in Finca Irlanda, a coffee farm in Chiapas, Mexico (Fig. 3). In each plot we assigned a unique number to each coffee plant, recorded which coffee plants were patrolled by A. sericeasur or other ants, and sampled spiders. We also sampled the webs of Pocobletus in coffee plants that were and were not patrolled by A. sericeasur.

 

Figure 3. At finca Irlanda, before sampling spiders.

 

We were very excited by our results. We discovered that the spatial distribution of Pocobletus spiders is indeed strongly associated with A. sericeasur. In addition, we found that the webs of Pocobletus spiders have more prey items in the presence of A. sericeasur than in its absence.

Figure 4. Pocobletus sp. and its predators. Notice the small Pocobletus in the lower section of the web and the slightly bigger Argyrodinae spider in the upper part.

 

We were also very surprised to discover that Pocobletus spiders have a wide variety of predators, and that these predators are other spiders! (Fig. 4). But we were even more surprised when we found out that the abundance of these predators decreases in the presence of A. sericeasur. So, contrary to what you might expect, a coffee plant full of bustling A. sericeasur ants can be a great place for a tiny spider to be, with plenty of food and fewer enemies. If you want to know more about this research, read our paper to find out the whole fascinating story!

Linda marin and co-authors

I hope you haven’t missed that Oikos from 2015 changes cover each month! The photo for each issue is from one of the papers. The January cover photo was taken by David W. Inouye. The paper in questions is “Phenological shifts and the fate of mutualisms” by Nicole Rafferty and co-workers.

Here’s David’s description of the photo:

A male Broadtailed Hummingbird (Selasphorus platycercus) visiting a flower of dwarf larkspur (Delphinium nuttallianum) near the Rocky Mountain Biological Laboratory, Gothic, Colorado, USA. The hummingbirds are common at this site, and the larkspur flowers can carpet meadows early in the summer; they are an important nectar source for the birds at the beginning of the breeding season. The male hummingbirds have a slot between their first two primary feathers (visible in the photo), which makes a loud trilling noise as they fly. Nikon D200e camera with a Nikkor 70-200mm lens at 155mm, Nikon R1 flash, iso 250, 1/250 sec, f20.

Herbivory may be changed by climate change and how does that affect the host plants? Find out in the Early View paper “Colonization of a host tree by herbivorous insects under a changing climate” by Kaisa Heimonen and co-workers. Below is their summary of the paper: Climate warming is predicted to increase the abundance of herbivorous insects due to increased survival, growth and multivoltinism. In addition, due to warming climate many insect species are predicted to shift their ranges to higher latitudes. Host plants are adapted to the present day herbivore pressure and insect communities but in the future the abundance of insects and the composition of herbivorous insect communities might change which can lead to more intense herbivore damage. We wanted to study the susceptibility of silver birch (Betula pendula Roth) populations from different latitudes to the insect herbivores that are expected to spread northwards in the future. To do this we established three common gardens with 26 genotypes of silver birch from six latitudinal populations in Finland ranging from 60°N to 67°N. The common gardens were located at three different latitudes 60°N, 62°N and 67°N. At each study site 260 silver birches were growing. This experimental setup is being used also for several other studies (see the project homepage: http://www.uef.fi/fi/birchadaption).

Figure 1. Map showing the three common garden sites (filled squares) and the six source populations (filled circles). Mean annual temperature isoclines are shown in grey.

Figure 2. The three common garden sites in Finland where the study was conducted. A) Southern study site is located in Tuusula 60°N, B) Central study site is located in Joensuu 62°N and C) Northern study site is located in Kolari 67°N. Photo credits: Kaisa Heimonen.

We wanted to study how the local insects at each of the common garden sites colonized the translocated birch genotypes. We asked if the insect herbivore density, species richness or community composition could be explained by the source population of the birch or by the direction or distance of the latitudinal translocation. The herbivore community on the study birches was examined during two growing seasons in 2011 and in 2012.

Figure 3. Kaisa Heimonen (lead author) observing the herbivorous insects on silver birch at the northern study site in 2012. Photo credits: Sari Kontunen-Soppela.

Herbivore density among the source populations differed in 2012 but not in 2011 and species richness was not affected by the source population. Latitudinal translocation could not explain the variation in the herbivore density or in the species richness. Community composition of the herbivores differed among the source populations at two of the three study sites and the similarity of the herbivore communities decreased with increasing latitudinal distance of the source populations.

Figure 4. Common insect species on silver birch belonging to the orders Lepidoptera, Coleoptera and Hymenoptera. A) White-shouldered smudge (Ypsolopha parenthesella), B) Birch leaf roller (Deporaus betulae) and C) Early birch leaf edgeminer (Fenusella nana). Photo credits: Kaisa Heimonen.

Silver birch genotypes from source populations originating from closer geographical distance had more similar herbivore community composition at our experimental sites possibly because they are genetically more similar than the geographically more distant birch genotypes. All birch genotypes were colonized by some of the local herbivores at all three study sites suggesting that in the future herbivorous insects are able to colonize novel host plant genotypes. The results of this study show that compositional changes in the insect communities on their host plants are expected in the future. Newly structured herbivore communities might affect the herbivore damage and thereby also the plant growth.

 

Fig. 1. Recently metamorphosed green frog (Lithobates clamitans) at the edge of a pond (photo by Laura Martin)

 

Fig. 2 American toad (Anaxyrus (Bufo) americanus) adult (photo by Carrie Brown-Lima) American

 

Amphibians develop in watery places that are full of plants. And yet we know little about how these plants affect larval amphibians. As disease, climate change, and land-use change continue to threaten amphibian populations worldwide, it is more important than ever to understand what makes for good amphibian habitat.

 

 

Fig. 3 Shauna-kay Rainford at Bear Swamp, NY, one of the litter collection locations(photo by Laura Martin)

 

In the study “Effects of plant litter diversity, species, origin and traits on larval toad performance,” Cornell undergraduate Shauna-kay Rainford (now a graduate student at Penn State University), graduate student Laura Martin, and Professor Bernd Blossey investigated how plant litter communities influence the growth and survival of Anaxyrus americanus (American toad) larvae. They reared tadpoles in singles species and litter mixtures using 15 native and 9 nonnative plant species common to central New York, USA, recording survival, time to metamorphosis, and growth rate.

 

 

Fig. 4 Microcosms in which individual larval amphibians were reared in leaf litter treatments. (photo by Shauna-kay Rainford)

 

Survival in single species treatments ranged from 0% (in Rhamnus cathartica litter) to 96% (Pinus strobus). Tadpoles also failed to metamorphose in Acer rubrum, Cornus racemosa, Rosa multiflora, and Tsuga canadensis. Percent metamorphosis was highest in nonnative Lonicera spp. (76.7%), native Phragmites australis americanus (73.3%), nonnative P. australis (60.0%), and nonnative Alnus glutinosa (60.0%). Interestingly, whether the plant was native or nonnative did not affect amphibian performance.

In multi-species treatments, number of plant species had no effect on larval survival or metamorphosis. However, larvae reared in mixtures of 3 species were larger than those reared in single species treatments of the same species. But increasing litter diversity to 6 or 12 species did not further improve larval survival or performance. This result is consistent with analyses that reveal that most ecological processes saturate at relatively low levels of diversity.

Currently, understanding of the relationships of biodiversity and ecosystem function is drawn largely from studies of plant communities in temperate grassland ecosystems. But the vast majority of plant material is not consumed green; it enters detrital food webs like the one studied in this experiment. This study is an important first step towards understanding the mechanisms that underlie plant-amphibian interactions. It further highlights the importance of plant traits, but not origin, when considering amphibian habitat restoration and conservation.

Invasive species have negative economic and environmental consequences worldwide and, in our changing world, it has become increasingly important to understand their impacts. However, when assessing the impacts of invasive species, scientists often compare un-invaded sites with highly invaded sites, representing the ‘worst-case scenario’. Consequently, there is little information on how the impact of invaders varies with their population size. In the Early View paper “Population density modifies the ecological impacts of invasive species” we use experimental ponds to assess how ecological impact varies across different population densities for a model invasive fish (Pseudorasbora parva).

We examined the relationship between density and impact to develop density-impact curves (see attached figure). We found both linear and non-linear density-impact curves for different direct and indirect ecological impacts. For instance, the relationship between fish density and zooplankton biomass and abundance was a high-threshold curve, indicating a smaller impact than a linear relationship would predict.

We also found density-impact relationships that were linear, low-threshold or s-shaped. Therefore, we caution against
the common assumption that ecological impact increases linearly with invader density. An understanding of the relationship between invader population density and ecological impact can assist in developing realistic and sustainable management strategies for controlling the negative impacts of invaders.

The potential relationships between invasive population density and
ecological impacts. Re-drawn from Yokomizo et al. (2009, Ecological
Applications; DOI:10.1890/08-0442.1).

Michelle C. Jackson and co-authors

Do migratory birds catch more parasites? This is explored in the Oikos Early View paper “Flying with diverse passengers: greater richness of parasitic nematodes in migratory birds” by Janet Koprivnikar and tommy L.F. Leung. Below is their short summary of the study:

Many different animals undergo annual migrations and some of them cover enormous distances with their journey. This undertaking can be extremely strenuous and physiologically demanding. Aside from the demands of the journey itself, most animals don’t travel alone – they carry with them an entire community of different parasites throughout their body. Migratory birds undergo annual migratory flights across the globe and birds are well known to be a haven for
pathogens. Most birds are infected with dozens of different species of parasite, many of them worms of all shapes and sizes. While most studies looking at bird parasites in relation to their ecology or migratory habits have focused on blood-dwelling types such as avian malaria, few have studied their worms despite the relative abundance of these parasites in their hosts. Of those different types of worms, the most harmful are the nematodes (roundworms). Some nematodes can cause serious diseases in birds so we decided to compare the diversity of parasitic roundworms in migratory birds versus that of non-migratory species.

In particular, we focused our attention on three orders of birds; water birds (Anseriformes), perching birds (Passeriformes), and birds of prey (Accipitriformes). We found that for any of those given orders, the migratory species tended to have a wider range of roundworms than non-migratory species. Furthermore, we also found that bird species which have proportionally larger spleens also happen to have a greater variety of roundworms infecting them.

Fig. 1: A migratory bird species (Anas platyrhynchos – the mallard duck) reported as a host for 69 different species of roundworm.

Fig. 2: Mean nematode species richness (corrected for host study effort) + S.E. for migratory and resident bird species in the Anseriformes, Accipitriformes, and Turdidae (N = 188).

So why do migratory species have more diverse nematode communities than their non-migratory relatives? We don’t know that at this point. It is possible that migratory birds pick up many different species of parasites during their journey whereas non-migratory species which stick to a single location their entire life are exposed to a more limited range of parasites. Or perhaps because migration is such a stressful exercise, migratory birds can become stressed during such journeys and become more vulnerable to a wider variety of parasites. Or it might be both!
Due to the diseases that parasitic roundworms can cause in birds, it is important to also keep them in mind when considering the effects that global perturbations such as climate change can have on the ecology of migratory species. As migratory birds change their arrival and departure timing, and are also forced to alter their migratory routes and stopover sites, they might become more stressed and susceptible to parasitism. Furthermore, altered migratory routes and stopover sites can also mean that migratory birds might be introducing their rich suite of worms to new areas and potential hosts.

Moving to a new site for next brood? Good or bad? And why? These questions are answered in the Early View paper “Mechanisms and reproductive consequences of breeding dispersal in a specialist predator under temporally varying food conditions” by Julien Terraube and co-workers.

In this study, we explored the factors linked to variations in breeding dispersal behaviour and their consequences in terms of reproductive parameters in a raptor species. Which factors influence individual dispersal decisions? Are Eurasian kestrels Falco tinnunculus able to increase their own reproductive success after moving from one site to the other between two consecutive breeding seasons? Is this relationship mediated by environmental factors like food abundance or individual traits like gender or age? All these fascinating questions are hard to answer particularly in avian predators because of methodological limitations associated to size of the study area and even more in species like Eurasian kestrels breeding in boreal ecosystems, which have high breeding dispersal propensity and in which movements are driven by cyclic fluctuations in abundance of main foods (voles) (see Vasko et al. 2011).

In spring 1977, a long-term study of a local kestrel population breeding in western Finland (the Kauhava region) was initiated along with the monitoring of Tengmalm’s owl populations (see Korpimäki and Hakkarainen 2012). Hard work in the field has generated a fantastic long-term, large-scale dataset combining data from breeding success and individual traits of breeding kestrel parents captured at their nest sites over the last 25 years (1983-2013).

 

A +1-year old male kestrel on hand after trapping. Photo: Erkki Korpimäki.

Given the increasing demand for long-term population studies in order to understand current impact of environmental changes, the authors would like to stress the importance of long-term studies on demographic parameters in long-lived vertebrate populations. In this study, the assessment of breeding dispersal distances was made possible through systematic capture of most kestrel parents breeding in the main study areas, ringing and recovery of previous rings. We would like to focus here on the capture procedure that allowed collecting breeding dispersal data and share the experience acquired during the hours spent in “Wild-West” of Finland when checking traps.

 

Three-week old nestlings in the nest-box. Photo: Erkki Korpimäki

Capture occurs during the brood-rearing period when chicks are two-to-three weeks old, in order to avoid unnecessary disturbance of young nestlings during the most vulnerable phase. Virtually all the breeding population monitored breeds in nest-boxes that were set up on barns from early 1980s onwards. The total number of nest-boxes has varied from 350 to 450 throughout the study period in agricultural fields of the study area. We have used swing-door traps attached to the front of the nest box for trapping parents. The “trapping routine” starts by erecting the traps early in the morning from 5-6 am on a group of 5 to 10 breeding sites selected according to nestling age. Then trap-checking rounds are performed every two-to-three hours to check if any individual is trapped. The aim is to capture both female and male from each breeding site within 12 hours. Adults are ringed, measured and weighed near the breeding site and released as soon as possible. A capture day ends by giving newly-hatched rooster chickens to the kestrel nestlings to compensate for the decrease in prey delivery rates experienced during the trapping of their parents.

We have been lucky in the sense that voluntary birdwatchers and ringers have set up many large nest-box networks for kestrels in surrounding areas in western Finland. In addition, many voluntary ringers, particularly Erkki Rautiainen and Jussi Ryssy, have also made huge efforts to trap and ring kestrel parents and to ring fledglings at these nest-boxes.

A female kestrel with metal and colour rings in the front of the nest-box. Photo: Benjam Pöntinen.

A total of 2089 males and 2544 females were trapped at nests during 1985 to 2011 in our study areas. Trapping success remained relatively constant over the period: of all the nesting attempts on average 70% of the male and 80% of the female parents were successfully captured yearly. This large-scale trapping and ringing program allowed us to collect 631 dispersal events from 1985 to 2011 that were analysed in this study.

Overall, we found that females dispersed further than males and older individuals dispersed further than yearlings. A noteworthy aspect of this study involved the evidence of body-condition dependent dispersal strategies in kestrels as the individual body condition index was positively correlated to breeding dispersal distances, particularly in females. Strikingly, our results also evidenced complex patterns of non-linear relationship between previous breeding success and dispersal distances. Finally, longer dispersal distances were associated with reproductive costs in males under increasing vole abundance, whereas those females dispersing further increased their breeding success under all conditions of food abundance.

These results call for further research as clearly there is more to learn about the link between potential pre- and post-breeding prospecting movements, optimal dispersal decisions and population dynamics in avian predators inhabiting fast changing boreal ecosystems.

 

References

 

Korpimäki, E. & Hakkarainen, H. 2012. The boreal owl: Ecology, Behaviour and Conservation of a Forest-Dwelling Predator. – Cambridge University Press, Cambridge. 372 pages.

 

Vasko, V., Laaksonen, T., Valkama, J. & Korpimäki, E. 2011. Breeding dispersal of Eurasian kestrels (Falco tinnunculus) under temporally fluctuating food abundance. – Journal of Avian Biology 42: 552-563. (doi: 10.1111/j.1600-048X.2011.05351.x)

Timing is everything. For an interaction to take place, organisms not only have to be at the same place, they need to be there at the same time. The timing of flowering has likely been an important trait ever since the first flowers appeared on Earth ~200 million years ago; and when the climate changes, phenological changes belong to the most striking ecological responses. The timing of biological events is an important and exciting phenomenon in life-history evolution.

There is currently widespread concern that climate-driven changes in the timing of seasonal events may disrupt important ecological interactions such as pollination or cause temporal mismatches between critical periods in animal life-cycles and food availability. Phenological change has received substantial attention and has also been treated in thematic issues in other journals. This thematic issue of Oikos, however, has a more specific focus on the interplay between phenology and ecological interactions and on understanding phenological change from the perspective of life-history evolution. The articles, contributed by ecologists with expertise in phenology and/or theoretical ecology represent a wide range of scientific approaches. The volume contains theoretical investigations emphasizing the role of phenology in meta-community networks (Revilla et al.), in evolutionary games (Day and Kokko, Schmidt et al.) and in density-dependent population dynamics (Reed et al.). It also contains field studies of timing of reproduction in species adapting o climate change (Bennet et al., Van Dyck et al.) and experiments showing how timing of germination influences interspecific competition among plants (Cleland et al.). Among the contributions are furthermore reviews and conceptual papers on phenological change in the context of plant-pollinator interactions (Forrest), mutualisms in general (Rafferty et al. ) and plant life histories (Ehrlén) along with a synthesis of theory emerging in this field (Johansson et al.).

Phenological data continues to accumulate in ongoing, large-scale monitoring programs and we have increasingly refined methods to monitor changes. However, so far our knowledge has to a large extent been descriptive and any explanations for observed phenology patterns have been proximate and focused on abiotic influences. This special issue deals with how ecological interactions influences phenological patterns and vice versa. Some of the contributions have also provided ultimate explanations to phenological processes and patterns. That way, this issue offers a novel take on an old research topic and it provides a snap shot of the latest developments in this exciting research area.

Jacob Johansson, Jan-Åke Nilsson and Niclas Jonzén, editors of Oikos issue “Phenological change and ecological interactions”

We are very happy to welcome Dr. Francois Massol to Oikos Editorial Board. Get to know him here:

What’s your main research focus at the moment?

These days, I try and focus my efforts on the evolution of dispersal and the evolutionary ecology of interaction networks. What I want to understand is how some traits and some particular positions in ecological networks come to be associated with a given propensity to disperse. This issue is important from a fundamental viewpoint – it relates to the knowledge of so-called “dispersal syndromes” – but it is also a hot issue from a more applied perspective because it could help understand the evolutionary emergence of would-be invasive, keystone or easily threatened species. Given my personal bias towards equations and theory, I tend to first confront these issues using models and then collaborate with more empirically minded colleagues to test theoretical predictions with field or experimental data.

However, when I write “focus my efforts”, I have to acknowledge that I spend quite a significant fraction of my time away from my usual favourite subjects, working on interdisciplinary projects (mostly with social scientists and physicists) – and I am rather thankful for these little eccentricities, for they help me broaden my perspective of theoretical approaches to modelling the dynamics of biodiversity.

Can you describe you research career? Where, what, when?

Coming from a typically French undergrad background (maths and physics), I switched to ecology and evolutionary biology during my Master and then my PhD in Montpellier, under the supervision of Philippe Jarne at the CEFE. My work at that time was focused on community ecology models. After I graduated, my first position was at the Irstea Hydrobiology lab in Aix-en-Provence, to work on more functional aspects of aquatic communities. While I was employed at Irstea, I obtained a Marie Curie fellowship that allowed me to spend a year (2009 – 2010) in Mathew Leibold’s lab in Austin, Texas, where I tried to run a mesocosm experiment dealing with the effect of dispersal on the functioning of food webs (sadly, the experiment failed, but this is another story). In 2012, I was recruited at the CNRS in Montpellier (back to the CEFE), in the group of Pierre-Olivier Cheptou, to work on the evolution of mating systems and dispersal traits in plants. In 2013, I moved to a CNRS lab in Lille (GEPV) where I joined the group of Sylvain Billiard to work on the evolutionary ecology of mating systems. Moving so frequently is both a boon and a curse for obvious reasons, but as a connoisseur of the evolution of dispersal, I try to wear this as a badge of honour (and humour).

How come that you became a scientist in ecology?

If I were to explain why I became a scientist based on personality and motivations alone, curiosity together with the possibility of working in a free-thinking environment surely had a role at some point. I would also add that my personal kind of stubbornness probably helped a lot in getting me there. However, I think it’s also quite enlightening to think of a career path in science as built half on motivations and half on contingencies. The original contingency that set me on track was the first scientific internship I did back in 2002 in Dima Sherbakov’s lab at the Limnological Institute in Irkutsk, Russia. The atmosphere in the lab, the way people were working, the passion that permeated the place – all of this probably triggered something in my mind and I have been fond of this ambience ever since. The second set of happy contingencies have been the genial encounters I made afterwards when I was looking for a PhD project, i.e. Daniel Gerdeaux and Philippe Jarne, and then during my PhD (Pierre-Olivier Cheptou, to name but one person). I am convinced that a large part of my day-to-day satisfaction at work is based on the variety and the general goodwill of the colleagues with whom I interact.

What do you do when you’re not working?

At the moment, I am quite busy taking care of the house we just bought. House chores, family and friends occupy a consequent share of my non-lab time… Generally, I tend to spend the rest of my spare time reading (Terry Pratchett, Neal Stephenson, John Le Carré, Jasper Fforde and Neil Gaiman are always on top of the list), hiking, traveling and playing badminton.

Personal webpage: https://sites.google.com/a/polytechnique.org/francoismassol/home

ResearchGate page: https://www.researchgate.net/profile/Francois_Massol

 

The complicated predator-prey interactions are one of the most fascinating fields in ecology. They have been studied for decades, and the more we learn, the more surprising and unpredicted stories that we find. For me, finding that small rodents (lemmings) in the high Arctic may affect the populations of waders on the coast of Australia, New Zealand or South Africa was a real amazement.

Lemming populations have been known to show 3-5 years cycle, driven by either top-down or bottom-up control. In the Early View paper “Loss of periodicity in breeding success of waders links to changes in lemming cycles in Arctic ecosystems”, we have studied the interactions between the breeding success of high-Arctic nesting migratory shorebirds and lemming abundance, as they were suggested to be linked via the ‘alternative prey hypothesis’: In years of low lemming abundance, their predators, mainly Arctic fox, would switch to alternative prey, including chicks and eggs of shorebirds. In light of the large amount of evidence that lemming cycles have now changed and even disappeared in some parts of the Arctic, we found that the breeding success of these migrants used to follow the cycles of lemmings, but these cycles have too started to disappear, suggesting a cascading effect of changes in lemming cycles.

Siberian lemming © Pavel Tomkovich

The reason for these changes in lemming cycles is still not entirely known. One possible explanation is that climate change caused alteration of the snow structure which is a crucial hiding and feeding place for lemmings during winter. It might also be the natural tendency of populations in nature to go in and out of cycle. As shorebirds are known to consume considerable amount of benthic invertebrates, these changes in lemming cycle in the high Arctic potentially not only affect shorebird populations in the other side of the worlds, but also have a far-reaching cross-systems consequences on the ecosystem on the southern hemisphere.

 

Perfectly camouflaged shorebird chick with its ‘not so camouflaged’ parent, on the beautiful high Arctic breeding grounds © Pavel Tomkovich

 

Who will eat me and how fast will I be out-competed? Questions about the future for eucalyptus seedlings in a kangaroo world. Read more in Early View paper “Associational refuge in practice: can existing vegetation facilitate woodland restoration?” by Rebecca S. Stutz and co-workers. Below is their own summary of the study:

The characteristics of plant patches influence whether and how herbivores search for, detect and consume particular focal plants. Neighbouring plants may disrupt this foraging process at any phase, providing associational plant refuge for a focal plant. If we understand how and why this occurs, we may be able to improve revegetation efforts by planting strategically amongst existing vegetation to maximise their chances of escape from herbivory. We tested the capacity of existing vegetation in a degraded area of Booderee National Park, eastern Australia, to provide refuge for eucalypt seedlings from abundant mammalian herbivores. We quantified a suite of variables at large and small patch scales and used field cameras to confirm which herbivore species was responsible for seedling consumption.

Swamp wallabies were the principal browsers of seedlings. When they detected a seedling, they almost always decided to consume it, usually completely. At the larger patch scale, seedlings escaped browsing by swamp wallaby for longer in patches with fewer browsed plant species and those dominated by ferns rather than grasses. Higher understorey cover provided refuge for seedlings at the small patch scale. These characteristics are all consistent with disruption to the search and detection phases of the foraging process, and therefore the occurrence of associational plant effects. Lower canopy cover at the large scale also reduced browsing but the mechanism may be through its influence on microclimate, probability of finding seedlings below-canopy, or perceived predation risk. Our study demonstrates that existing patch characteristics can both provide associational plant refuge and influence patterns of herbivore foraging more generally.

Photos 1 & 2: Our focal seedling Eucalyptus pilularis before and after browsing by a swamp wallaby.

A swamp wallaby discovers a eucalypt seedling.

How species may cope with global warming is studied in the Early View paper “Geographic mosaics of phenology, host preference, adult size and microhabitat choice predict butterfly resilience to climate warming” by Nichole L. Bennett and coworkers. Below is their summary of the study:

Scientists investigating biological response to climate change have traditionally focused on how species move in space or in time to track the “climate envelope” (range of climatic conditions within which a species can survive). However, many species are able to buffer the effects of overall climate through habitat use. For example, the black-veined white butterfly, Aporia crataegi, achieves the same egg temperatures at both low and high elevations in Spain by laying eggs on the cool north-facing sides of host plant bushes at low elevation and on the warm south-facing side at higher altitudes¹. Our study organism, Edith’s checkerspot butterfly, Euphydryas editha is known to be climate-sensitive and associates with a variety of host plants. It also exhibits between-population variation in peak flight time, so this study system provides an excellent system to investigate the options available to a species with diverse habitat use and diverse seasonality in a warming world.

Suitable egg-laying site choice is critical to egg and caterpillar survival. Newly-hatched larvae do not travel far from the site where eggs were laid and normally begin feeding on the plant chosen by their mother or a nearby plant. Edith’s checkerspot feeds on plants in the families Plantaginaceae (Collinsia, Plantago, Penstemon) and Orobanchaceae (Pedicularis, Castilleja). Butterflies lay their eggs on their principal host plant in a complex spatial mosaic^2,3. Populations that feed only on Pedicularis and populations that feed only on Collinsia differ in a suite of adaptations^2,4,5. For instance, butterflies that are adapted to Pedicularis lay their eggs low on the plant while butterflies adapted to Collinsia lay their eggs higher up on the plant. We became interested in the consequences of host plant adaptation, especially egg-laying height, for the thermal environment of the eggs and newly-hatched larvae.

Butterflies adapted to Pedicularis lay their eggs low.

Butterflies adapted to Collinsia lay their eggs high.

To investigate whether egg-laying height influenced egg thermal environment, we measured heights of egg clutches, egg clutch temperature, and ambient temperature at eight field sites. No matter what plant was used, eggspace temperatures decreased with increasing egg height on plant, with hotter temperatures near the ground. To determine how much “wiggle room” these butterflies have for future warming, we asked if eggs could be laid at cooler microsites (i.e. higher) on the same plants. Eggs at seven of the sites were laid as low as possible, and there was only one population where the eggs were laid as high as possible on the plant. So, Edith’s checkerspot butterfly seems to retain options for buffering future warming with regard to host plant microclimate.

Populations of the butterfly also vary drastically in timing of peak flight season, and we were interested in the thermal consequences of this variation. Using a combination of observations and museum records⁶, we found that peak flight season varies between March and July. From the PRISM climate mapping system, we retrieved the mean daily maximum temperatures for each site (averaged over 1970-2000 in a 800m² grid)⁷. We determined a measure of “phenological mitigation” by subtracting July temperatures from temperature during peak flight season. This gave us an idea of whether or not butterflies are flying earlier to avoid hotter temperatures. The positive association between July temperature and “phenological mitigation” suggests that butterflies are buffering overall hot climates by flying earlier during cooler months. We also asked if cooler, earlier flight times are available to the butterflies to buffer future warming. In twelve of fifteen sites, caterpillars started growing as early in the year as it was possible for them to feed. At these sites, any advance in timing would happen at the expense of adult size and the amount of offspring produced. At the three remaining sites, this sort of shift was possible without shortening time for growoth.

Despite the known climate sensitivity of Edith’s checkerspot butterfly, we expect that this species’ potential for rapid evolution⁸ and variation in habitat use² will enable it to persist across most of its range as climate warms. However, particular subpopulations may prove extremely vulnerable. A prime example is the federally endangered Bay Checkerspot, Euphydryas editha bayensis. Although it is located near the center of the species’ latitudinal range, the Bay Checkerspot operates close to the limits of its ecological tolerance⁹.

We wish to thank Jacob Johansson, Niclas Jonzén and Jan-Åke Nilsson for inviting us to contribute with our paper to the special issue about “Phenological change and ecological interactions.”

References

1.  Merrill, R. M. et al. J. Anim. Behav. 77, 145 (2008).

2.  Singer, M. C., McBride, C. S. Evolution. 64, 921 (2010).

3.  Mikheyev, A. S., et al. Mol. Ecol. 22,4753 (2013).

4.  Parmesan, C., Singer, M.C., Harris I. Anim. Behav. 50,161 (1995).

5.  Parmesan, C. J. Insect Behav. 4, 417 (1991).

6. Parmesan, C. Nature. 382, 765 (1996).

7.  PRISM Climate Group. Oregon State University (2004).; http://prism.oregonstate.edu

8.  Singer, M.C., Parmesan, C. Nature. 361, 251 (1993).

9  Singer, M. C., Parmesan, C. Phil. T. Roy. Soc. B. 12, 3161 (2010)

Welcome to Oikos’ Editorial Board, Dr Andrew MacDougall, University of Guelph. Visit his webpage here. And read more about him below:

1. What’s you main research focus at the moment?
How the co-varying influences of global environmental change transform fundamental processes relating to diversity and function in terrestrial systems

2. Can you describe your research career? Where, what, when?
I have been at the University of Guelph since 2006; prior to my PhD, I worked for several years as a government research biologist in eastern Canada.

3. How come that you became a scientist in ecology?
a love of the outdoors, and a curiosity about the workings of the natural world

4. What do you do when you’re not working?
[laughter] being dad, road biking, yoga

The last issue from 2014 is online.

We selected the meta-analysis by Kulmatisk et al on the impact of soil foodwebs on plant growth  and the forum on the relative importance of neutral stochasticity in community ecology by Vellend et al. as editor’s choice. These two papers create synthesis in community ecology. The first by pointing the first widespread support for the presence of trophic cascades in soils, the second one by providing conceptual clarity on the main prevailing stochastic processes in community dynamics.

 

Kulmatisk and colleagues conducted a meta-analysis based on 1526 experiments that measured plant growth responses to additions or removals of soil organisms to test how different soil trophic levels affect plant growth. They demonstrate the top down control by predators and parasites on belowground herbivory and estimate the impact of belowground biota on plant growth overall positive and strong. Omnivory in the soil food web generally increases plant productivity by (i) pest reduction and (ii) increasing nutrient cycling.

 

Vellend and colleagues continue to set the scene of community ecology. They address several profound philosophical, theoretical and empirical challenges on the relative importance of stochasticity in community dynamics. They clearly clarify differences between ‘stochastic’ or ‘neutral’ processes by synthesizing their importance in different community processes. They subsequently provide a guide how different observational and experimental approaches will forward the field by allowing a thorough understanding of the role of neutral stochasticity in community ecology.

 

Enjoy!

Dries Bonte, Editor in Chief

Very welcome, Dr Sara Magalhaes, to the Oikos Editorial Board! Get to know Sara by visiting her webpage and read the mini-interview here:

1.     What’s you main research focus at the moment?

I work mainly with spider mites, which are herbivorous haplodiploid tiny spider-like creatures. Being easy to rear and with a short generation time, spider mites are easily amenable to experimental evolution, a methodology I find very powerful. With these mites, I ask questions within the general fields of host-parasite interactions (in which mites are either the host or the parasite), sex allocation, and mating strategies. I also do collaborative work on fruit flies, again on these topics.

2.     Can you describe you research career?

I did my undergraduate education at the University of Lisbon, with an Erasmus in Toulouse, then moved to the University of Amsterdam. There, I ended up doing my PhD thesis, under the supervision of Maurice Sabelis and Arne Janssen, and a lot of help from my colleagues Marta Montserrat, Belen Belliure and Maria Nomikou. The thesis concerned mainly the ecological consequences of antipredator behaviour. By the time I ended the thesis, in 2004, I felt the need to address the evolution of traits as well, so I moved to Montpellier to do a post-doc with Isabelle Olivieri. I took the mites with me and did experimental evolution of mite adaptation to novel host plants. I then decided to go back to Portugal, where I did a brief post-doc at the Gulbenkian Science Institute, again with experimental evolution but with bacteria and nematodes. Finally, in 2008, I came back to the University of Lisbon, where I established my own group with spider mites and several really cool students.

Photo: Jacques Denoyelle

3.     How come that you became a scientist in ecology?

I always thought that integrative sciences were more interesting. People that spend their whole lives studying a single molecule still give me the creeps, although I realize that this is also necessary…

4. What do you do when you’re not working?

I used to do lots of different stuff, I was in theatre groups, and danced tango a lot, went to lots of concerts and to the movies, but now that I have small kids my activities have switched to going to playgrounds and kid parties. In the summer, which in Portugal lasts around 6 months, it’s nicer because we go to beach, which everybody loves.

 

Human activities drastically reduce biodiversity at various taxonomic levels. While much of the current effort in research and biological conservation focuses on species diversity, the importance of intraspecific genetic diversity is sometimes overlooked. At the same time, genetic diversity within and among populations is the fundamental unit of biodiversity because it provides raw material for the adaptation, evolution and survival of species and individuals.

Plantation forests are usually composed of selected stock bred for desirable silvicultural properties (e.g., rapid growth rate and high timber quality) and as a result often have a narrower genetic basis than the wild populations of the same species. Even when natural regeneration is used, a limited number of seed trees may result in less diversity in the regenerated stand compared to the original one. Commercial applications of vegetative propagation of forest trees (clonal forestry) may lead to the further reduction in genetic diversity up to only a few or even a single genotype per plantation. For instance, micropropagation is commonly used to clonally multiply superior birch genotypes in Finland, both for commercial production and for breeding purposes, but it has been proven successful for only a limited number of birch genotypes. Limited number of commercially available birch clones may thus narrow the genetic diversity of planted birch stands.

Figure 1. Micropropagated birch planted inside plastic vole protector in 2000.

Limited genetic variation in plant stands can make them more vulnerable to pest invasion and outbreaks; if all the plants in a stand are genetically identical and susceptible to the same pest species, pest populations will spread rapidly from one plant to another. In agriculture, mixed planting of susceptible and resistant genotypes has been successfully used as a control tactic for plant pathogens in annual crops. However, the potential of using genotypes mixtures in plantation forestry for reducing pest damage has been little explored so far, although there are indications that mixtures may sometimes be of great value for controlling pests and diseases of trees as well, at least in short rotation energy forestry.

In this study, “Additive and non-additive effects of birch genotypic diversity on arthropod herbivory in a long-term field experiment”, now published Early View in Oikos,  we have experimentally tested whether genetic diversity of silver birch affects leaf damage by various arthropod pests. Silver birch (Betula pendula Roth) has broad distribution in the Northern Hemisphere and is one of the most important deciduous tree species in Finland, both ecologically and economically. In 2000, we established an experiment in Satakunta, SW Finland, by planting 8 different clones of silver birch which were obtained by micropropagation of vegetative buds of mature trees of southern Finnish origin. The eight clones selected for the experiment are known to differ in their growth and leaf characteristics as well as in resistance to herbivores and pathogens. The clones were planted in monoclonal plots and in different combinations of 2, 4 and 8 clones per plot. Damage by different types of arthropods was monitored on these experiments several times over nine years.

Figure 2. View of experimental area in 2014

 

Results show that genotypic variation and diversity strongly influenced birch herbivory, but that patterns varied among arthropod guilds and over time (within and across years). In particular, leaf-chewing damage and leaf galls were significantly less abundant in genotypically diverse stands than in stands with only a single genotype. However, leaf-rolling damage was actually higher in diverse stands, illustrating how arthropod guilds may differ in their responses to genotypic diversity.

 

A: leaf chewing by sawfly larvae.

B: leaf mining by Eriocrania sparmanella

C: leaf skeletonizing

D: leaf rolling

E: galls caused by eriophyid mites.

More detailed analyses at the genotype level revealed further interesting patterns. Genotypes varied considerably in their susceptibilities to most herbivore guilds examined, demonstrating that genetic variation existed among the 8 genotypes selected. Interestingly, the susceptibilities were not constant over time or among the guilds. This indicates that resistance to these guilds of herbivores is largely uncoupled genetically and that there is not a single genotype that is resistant to all types of herbivory. Furthermore, we observed shifts in the resistance rankings of genotypes between seasons and across years. Thus, while one genotype may be the most resistant to early-season leaf herbivory one year, it may not be the most resistant to leaf herbivory in the late season or the following year.

To try to understand the mechanisms underpinning the diversity effects observed, we used null modelling to test whether herbivory in diverse plots differed from expected levels generated from data in monoclonal plots. We found that diversity effects depended significantly on genotype, revealing that non-additive mechanisms operate in this system. In particular, more resistant genotypes often experienced greater than expected levels of herbivory (associational susceptibility) while more susceptible genotypes often had less than expected herbivory (associational resistance). These patterns indicate that associational resistance and susceptibility can occur simultaneously in genotypically diverse plots, presumably due to the reorganization of arthropods among genotypes. While these diversity effects do not scale up to influence plot-level rates of herbivory, they may strongly influence the fitness of plant genotypes within diverse plant stands, potentially playing a strong role in the evolutionary ecology of forest trees.

This study illustrates the value of long-term experiments for testing how genetic diversity influences the arthropod communities of woody plants. Diversity effects were complex and varied among the arthropod guilds, among the genotypes, and across time. Only by sampling multiple times over many years and including data for different kinds of herbivores did we detect these patterns. Future work looking at how plant phenotypes relate to these patterns and observing the behaviour of various arthropods can provide further insight into the mechanisms driving genotypic diversity effects.

Decades of ecological research have focused on interactions between herbivores and the chemical defenses of plants. However, far less is known about how effective physical defenses (spines, thorns, etc.) are against mammalian herbivores. It has been argued that co-evolution between plant physical defenses and herbivores might underly the confusing results across many studies.

Therefore, we conducted a study, now published Early View in Oikos “Evolutionary irony: evidence that ‘defensive’ plant spines act as a proximate cue to attract a mammalian herbivore”,  focused on the interaction between the white-throated woodrat (Neotoma albigula) and the cactus on which it specializes. There is great variation in how heavily-defended the cactus plants are, ranging from almost spineless to very spiny in the area where we study these animals (Castle Valley, UT, USA),

A white-throated woodrat (Neotoma albigula)

 

 

 

A nonspiny cactus plant

A heavily-defended, spiny cactus plant.

 

Woodrats collect large amounts of plant material in their nests that they feed on later. Interestingly, we noticed that the woodrat nests were covered mostly in heavily defended, spiny cacti. This phenomenon caused us to ask whether woodrats preferred spiny cacti, and why that might be.

A cactus plant collected from a woodrat nest. The bottom has been eaten by the woodrat.

 

We performed a number of feeding trials and choice experiments to show that indeed, woodrats do prefer spiny cacti to experimentally despined cacti. This result suggested that woodrats use the cactus spines as a cue for feeding. Nutritional analysis revealed that spiny cacti are lower in indigestible fiber and higher in protein than spiny cacti. We hypothesize that the woodrats may be using the signals of spines to collect a more nutrient-rich plant that they then feed on later.

Our results demonstrate that physical defenses can be overcome by specialist mammalian herbivores. Further, they show that mammalian herbivores can use obvious, visual clues to select plants that they want to consume.

The authors, through Kevin Kohl

 

Walk through a grassland at the peak of summer and you will quickly become aware of how many grasshoppers inhabit the area. But what effect do these grasshoppers and other insect herbivores have on the plant community you are walking through? How does the effect of invertebrate herbivores compare to that of less visible, but also ever present small mammal herbivores? And do these effects depend on the availability of resources? In our study, “Invertebrate, not small vertebrate, herbivory interacts with nutrient availability to impact tallgrass prairie community composition and forb biomass”, now on Early View in Oikos, we aimed to address these questions through an experimental study within a tallgrass prairie ecosystem in eastern Kansas. We factorially manipulated the presence of both invertebrate and small vertebrate herbivores and the availability of soil nutrients and observed changes in plant community composition and productivity over five years.

We found that removing invertebrate herbivores had a profound effect on plant community composition after a few years of treatment. Forb species increased in abundance in the absence of invertebrate herbivores, while grass species decreased. This effect was particularly strong under conditions of elevated nutrient availability. Surprisingly, small vertebrate herbivore removals had no detectable effect on grassland plant community composition or aboveground biomass.

A caterpillar chows down on a whorled milkweed (Asclepias verticillata), a plant species that greatly increases in abundance when invertebrate herbivores are removed from tallgrass prairie

 

Perhaps most interestingly, dispersion in community composition among plots where both invertebrate herbivores were removed and nutrient availability was elevated increased compared to the control plots. That is, different forb species came to dominate the replicate treatment plots, likely dependent on initial community composition. Overall, our research points to the important, and often overlooked, role that invertebrate herbivores play in structuring grassland communities. Future research aimed at continued investigation of the effects of invertebrate herbivory on plant communities would be worthwhile.

 

We welcome Professor Leif Egil Loe, Aas, Norway to the Oikos Editorial Board. Who is Leif Egil then? I asked some questions to get to know him better:

1. What’s you main research focus at the moment?

Most of what I am working on is related to ungulate ecology. I am involved in two long-term projects. The first is a population study of Svalbard reindeer initiated by Steve Albon and Rolf Langvatn in 1994 and still running on the 20th year. Current focusof that project is to understand mechanisms of population dynamics and aspects of life history evolution. I am also very interested in spatial ecology, so a subset of our reindeer is GPS-marked. One prediction from climate change is that ground icing events will happen increasingly often in Svalbard, and it has indeed happened two of the five years we have GPS-tracked animals. I am interested in the fitness consequences of different behavioural responses to such events. The second main project is a red deer study with Prof Atle Mysterud as PI. In the past few years we have focussed on the mechanisms of migration, again using GPS-data from several hundred marked red deer. Currently we have a stronger management focus, modelling functional management units and investigating how spatial harvesting patterns are predicted to be affected by climate change.

2. Can you describe your research career? Where, what, when?

I have a masters degree from the University of Oslo (UiO) and the University Centre in Svalbard (UNIS) from 1999 and a PhD from UiO in 2004. The title of the masters was “Habitat selection and site fidelity in Svalbard reindeer” (supervised by Nils Chr. Stenseth and Rolf Langvatn) and the PhD was entitled “Patterns and processes in the life history of red deer” (supervised by Atle Mysterud, Stenseth and Langvatn). From 2004 to 2010 I had researcher positions in Atle Mysteruds lab continuing to work on the red deer project. So as you see I have very much pursued the first two projects I encountered. Between 2008 and 2013 I worked with PhD student Anagaw Atickem on a Mountain nyala conservation project in Ethiopia that at least expanded my study topics geographically. In 2010 I was employed as an Associate Professor in wildlife ecology and management at the Norwegian University of Life Sciences. In 2013 I got promoted to full professor.

3. How come that you became a scientist in ecology?

I think I followed a fairly common path. For as long as I remember I always liked birds, especially feeding them during winter, drawing them and learning their names. In my teens I started collecting butterflies that was a main hobby for 3-4 years. The starting point was identifying species of birds and insects. Starting at university, I got interested in ecology. A study year in Svalbard, and especially meeting Rolf Langvatn, became influential in my career and primed me in on ungulate ecology. Taking a PhD in Stenseths Centre of Ecological and Evolutionary Synthesis, with Atle Mysterud as the main supervisor was fantastic – the best career start one can wish for.

4. What do you do when you’re not working?

I have two kids so a lot of time is devoted to family life. I am a keen small game hunter, like to hike and do cross country skiing in the forest and mountains. My favourite sports activity is “floor ball” that I play once a week.

Global biodiversity is constantly declining, and up-to-date research has shown that biodiversity loss affects the functioning of ecosystems and the services they provide to humans. Biodiversity-ecosystem functioning relations have yet mainly been analyzed in communities where species were randomly removed. In nature however, species are not lost at random, but according to their sensitivity to environmental stress.

In our study “Stressor-induced biodiversity gradients: revisiting biodiversity–ecosystem functioning relationships”, now published Early View in Oikos, we investigated whether biodiversity loss and biodiversity-ecosystem functioning relations in randomly composed diatom communities can be compared to those found in communities exposed to atrazine, one of the most-used pesticides worldwide.

Atrazine exposure resulted in smaller biodiversity loss, but steeper decrease in ecosystem functioning than in randomly assembled diatom communities. This was related to selective atrazine effects on the best performing species, which contributed most to ecosystem functioning but was also most sensitive to atrazine.

Our results imply that biodiversity loss and diversity-functioning relationships found along gradients of environmental stress do not compare to those inferred from the common approach of random community assembly. Species-specific sensitivity and performance need to be considered for a more accurate prediction of biodiversity and ecosystem functioning under stress.

The authors through Christophe Mensens

At first sight, these nematodes all look the same. Nevertheless, they each belong to a different species. Such cryptic species- species that morphologically look the same but show genetic divergence- are more different than we first might think. Previous research already showed that they have different environmental preferences and competitive abilities. In our paper, “Active dispersal is differentially affected by inter- and intraspecific competition in closely related nematode species”, we show that differences in active dispersal behavior occur: in addition to differences in time until first dispersal, the triggers for dispersal also differ between the species. One of the species is most triggered by interspecific competition, two others by competition with conspecifics, and the fourth one is a time-dependent disperser, with fast dispersal regardless of inter- or intraspecific interactions.

These differences in dispersal behavior may be important to explain the coexistence of these species. According to Darwin’s classical competition theory, we can expect that very similar species will not co-occur because competition will be too high. Differences in dispersal behavior may lead to postponed or avoided competition, rendering temporal coexistence possible in a patchy habitat.

The authors through Nele de Meester

Find out what role predation plays in the transfer of less complex parasites in the Early View paper “The underrated importance of predation in transmission ecology of direct lifecycle parasites” by Giovanni Strona. Below is his short summary of the study:

Predation is the primary route for transmission in parasites having complex life cycles. However, despite being one of the strongest evolutionary forces, little is known about its role in the ecology and evolution of simple life cycle parasites (that is parasites that spend all of their life on a single host).

Monogeneans are one of the most abundant group of fish parasites, and are peculiar in that they do not use more than one host during their whole life. Being well investigated, they constitute a good benchmark to explore if predation has some relevance for parasites when not directly involved in transmission from one host to another. For this, I used a large dataset and different approaches to test whether predators and preys share more monogenean parasites than one would expect from their geographical distribution, habitat preference and phylogenetic relationships. It turned out that preys and predators do share more monogenean parasites than expected.

The observed overlap degree was much higher at the genus level than at the species one. This suggests that predation may play an important role in promoting monogenean host range expansion. In addition, a good proportion of considered prey-predator pairs showed a significantly high parasite overlap at the species level. This last result promotes some intriguing hypotheses. In particular it may indicate a tendency of some monogenean parasites to evolve transmission strategies more targeted towards host interactions than towards species specific traits.

Monogenean parasites identify suitable hosts on the basis of various cues related to host physiology and behavior, such as shadows, chemicals, mechanical disturbance, and osmotic changes. Usually, these cues are generated by the activity of single species, but could also result from species interactions. For example, a predator hunting a school of fish may produce peculiar water turbulence, shadows, and specific chemicals, which are stimuli that have already been demonstrated capable of inducing mass hatching in monogeneans. Some monogenean parasites could have developed the ability to identify these cues, and to infect with similar probability a predator and its prey/s. If this hypothesis was true, it would have strong implications on evolutionary ecology, suggesting the existence of a peculiar situation, where some parasites have evolved high specialized host finding behaviors to become more generalist. Morevover, it would indicate that some monogenean parasites could be more vulnerable to coextinctions than suggested by the size of their host range, as their survival would depend on that of both the prey and the predator species.

Variation in size between sexes is something that we associate mainly with animals. But what about plants? Do female plants have larger leaves than males? Find out in the Early View paper in Oikos “Sexual size dimorphism in island plants: the niche variation hypothesis and insular size changes” by Patrick H. Kavanagh and Kevin C. Burns. below is their summary of the study:

Sexual size dimorphism (SSD) is common throughout the animal kingdom. Size differences between the sexes are often extreme and in many cases one sex may be twice the size of the other. While most plants are hermaphroditic, approximately 7% of flowering plants are dioecious (separate male and female individuals). SSD is also common in dioecious plants, yet has received far less attention than SSD in animals. The niche variation hypothesis predicts the degree of SSD to increase for insular populations as a response to increased intraspecific competition.   Many animal taxa conform to this prediction, however SSD of island plant populations had not been investigated.

We investigated differences in SSD between related island and mainland plants by using herbarium material. Specifically, we quantified the sizes of leaves and stems for plants from the New Zealand mainland and surrounding offshore islands. Our results suggest that the degree of SSD is not predictable for island plants, contrary to predictions of the niche variation hypothesis. Furthermore, SSD was consistently female biased on the mainland, however the direction of SSD was not predictable on islands. Our results suggest that both sexes are under selection for increased size on islands. This may contribute to SSD being unpredictable due to the sexes responding to selection at different rates. However, further work is needed to gain a better understanding of SSD in island plant populations.

In our new paper “Marine biodiversity and ecosystem functioning: what’s known and what’s next?” just published online early in Oikos, we synthesise our current understanding of the functional consequences of changes in species richness in the marine realm. For those familiar with the field of biodiversity and ecosystem functioning, the first question might well be: do we really need yet another meta-analysis on this topic? I mean, really. There have been several meta-analyses published in recent years. Do we really need this work?

Well, our answer to the question is yes. Here’s why.

This paper started while we were synthesising data for general biodiversity-ecosystem functioning relationships at NCEAS  in Santa Barbara, USA. We realised that much data from the marine side was missing, as many of those studies did not fit the inclusion criteria set up for our original database. Previous meta-analyses^{1, 2} focused solely on how richness influences resource capture and/or the production of biomass. Marine studies, however, all over the map in terms of what functions they measured: resource use, biomass production, nutrient fluxes, trophic cascades, and so on.

Panel with a sessile invertebrate community. Photo credit: Jarrett Byrnes.

 

So what’s the full picture of how biodiversity-ecosystem influences functions in the ocean – from primary production to biogeochemical cycles?

We got our hands on 110 marine experiments that manipulated the number of species and analysed some ecosystem response. In general, our analyses generally confirm previous findings that the average mix of species uses resources more efficiently and produces more biomass than the average monoculture. We honestly weren’t sure how this was going to fall out, and find great comfort in the generality of the result.

Soft sediment microcosms, Sweden. Photo credit: Karl Norling.

 

 

In contrast, we find a different shape to relationship between biodiversity and ecosystem functions than has been seen previously. The relationship between species richness and production is best described as linear. The relationship between species richness and consumption appear to follow a power function. We find this by using new and more powerful techniques to describing the shape of relationships across multiple studies that we hope future researchers will use as well. (And, yes, we give you all of our code so that you can follow along at home!)

A seagrass field experiment in Finland. Photo shows a polyculture with three species. Photo credit: Camilla Gustafsson.

 

We also identify several gaps in our understanding of marine biodiversity and ecosystem functioning that are ripe for future investigation. First, the number of studies focusing on biogeochemical fluxes is still tiny. We need more. Second, we need more studies in pelagic and salt-marsh environments. Third, we still have only a handful of studies focused on predators. Fourth, the effects of increases in species richness (e.g. due to invasives or range shifts) are poorly understood. And last, we really only looked at relatively simple experiments, using on average only 3 species! We sorely need experiments targeting how spatial scale and heterogeneity, realistic local extinction scenarios from natural (read: large!) species pools, and functional and phylogenetic composition alter the relationship between biodiversity and ecosystem function.

To sum: there’s much work to be done, and we look forward with high hopes to the next generation of experiments exploring the consequences of changes in marine biodiversity.

Three species of crab, used in the experiment in Griffin et al. 20083. Photo credit: Pippa Moore.

 

Now, if you had to explain this study to your mom or dad: the world has an incredible number and variety of different species, but we are losing them due to things like fishing, habitat destruction, and other threats from humanity. We need to understand what the consequences of these extinctions are for healthy and productive ecosystems, which is why researchers conduct experiments where they remove species and see what happens. We summarized data from 110 such experiments and found that losing species, on average, decreases productivity and growth, as well as a myriad of other processes related to how marine organisms capture and utilize resources, like nutrients. These processes ultimately put food on the dinner table and give us clean water. What is most interesting is we expected these declines to be non-linear based on previous studies: you can lose some species up to a point, then it starts to go downhill. The results from our analysis suggest that, for some processes, every species matters! Thus it is imperative that we protect and conserve biodiversity in our world’s oceans.

Lars Gamfeldt and co-workers

References:

1. Cardinale, B. J. et al. 2006. Effects of biodiversity on the functioning of trophic groups and ecosystems. – Nature 443: 989-992.
2. Cardinale, B. J. et al. 2011. The functional role of producer diversity in ecosystems. – American Journal of Botany 98: 572-592.
3. Griffin, J., de la Haye, K., Hawkins, S., Thompson, R. and Jenkins, S. 2008. Predator diversity effects and ecosystem functioning: density modifies the effect of resource partitioning. – Ecology 89: 298-305.

 

Conservation biologists and climate change researchers are worried by the observed phenological changes, that is, timing of biological events. These concerns are partly motivated by the expected species-specific and thus potentially non-parallell phenological shifts among interacting species, leading to what is often-named ’mismatches’ for ’plants (that) are finely tuned to the seasonality of their environment’.
These concerns are rarely accompanied by empirical data showing that phenological change leads to changes in fitness or population dynamics, and most often they focus on a single phase in the plant’s annual cycle. In our study, we observed the timing of flowering, fruiting, dispersal and germination and their effects on fitness components in the insect-pollinated, and bird-dispersed shrub Frangula alnus (Rhamnaceae).

Frangula alnus bicolored fruit display

In our study “Are mismatches the norm? Timing of flowering, fruiting, dispersal and germination and their fitness effects in Frangula alnus (Rhamnaceae)” we found that the effects of earliness (in phenological terms) varies between different phases and between different fitness components. Thus, we argue that the timing and temporal distribution of every single phase, e.g., flowering, fruiting or germination, is not at all finely tuned, but a robust compromise to selection pressures varying between phases and years.

Kjell Bolmgren and Ove Eriksson

The higher up, the smaller the insects…or? Dispersing insects might be different. Read more in the Early View paper “Dispersal potential impacts size clines of grasshoppers across an elevation gradient” by Richard Levy and colleagues. Below is the author’s own summary of the study:

Insects found across elevation gradients that experience seasonality are commonly observed to become smaller with increased elevation. This results primarily from a reduction in season length at higher elevations, which selects for individuals that mature as early as possible, despite losing the benefits of a larger body. However, our study finds that this pattern can be completely negated in species of grasshoppers that exhibit morphologies and behaviors that increase their dispersal. To see if the nullification of this evolved pattern influenced the reproductive fitness of large bodied, high elevation grasshopper populations, we brought females back from the field and allowed them to lay clutches of eggs in the laboratory. The grasshoppers were then dissected and the functionality of their ovarioles (female insect reproductive organs) was analyzed. While we did find that ovariole functionality decreased due to higher dispersal, we were unable to measure any effect on the size and number of eggs laid. Overall, our study provides evidence that dispersal among populations can reduce or counter traits evolved to best suit local conditions.

Ovarioles from Melanoplus pellucida

 

Melanoplus dodgei from alpine site

Ecologists strive to understand the causes of the observed variability in population abundance and distribution. 1/f noise models and multifractals provide complementary conceptual and analytical frameworks to characterise variability in temporal and spatial series of environmental and ecological data. In our paper, “Multifractal spatial distribution of epilithic microphytobenthos on a Mediterranean rocky shore”, we combined these techniques to investigate the spatial distribution of epilithic microphytobenthos (EMPB) forming biofilms on rocky intertidal surfaces.

Marine biofilms, which mainly consist of photosynthetic organisms (diatoms, cyanobacteria and spores of macroalgae) embedded in a polysaccharide matrix, are important but almost neglected components of rocky intertidal habitats. Indeed, they substantially contribute to coastal primary productivity, provide food for grazing gastropods and facilitate the settlement of algal propagules and larvae of sessile invertebrates. Previous studies investigating the spatial distribution of soft bottom biofilms and periphyton communities highlighted that these microscopic organisms form complex multifractal spatial structures. On the bases of these results we hypothesized that power laws and multifractals could best describe the spatial distribution of rocky intertidal biofilms. We tested this hypothesis applying spectral analysis and multifractal geometry to nearly-continuous EMPB biomass data, obtained from calibrated colour-infrared images.

Our results support the hypothesis that 1/f noise spatial patterns are also multifractal. We interpreted these findings from two different but not mutually exclusive perspectives: either as the result of the superimposition of several biotic and abiotic processes acting at multiple spatial scales or as the hallmark of self-organization. Both interpretations stress the importance of local biotic interactions, either positive or negative, in shaping spatial pattern of distribution of EMPB biomass, while differing in the way environmental processes are supposed to affect microalgal abundance. The first interpretation is that environmental processes associated with temperature, insolation and moisture exert a direct effect on EMPB. Conversely, under self-organization, the influence of these abiotic variables is indirect, being mediated by the presence of the polysaccharide matrix in which microalgal cells are embedded.

Martina Del Bello

As announced in the August issue, Oikos is publishing meta-analyses at an increasing rate, and similar to the transformative capacity of the Forum section, a dedicated section associated with formalized, replicable systematic reviews and meta-analyses will also advance discovery and integration via effective curation. Chris Lortie will act as EiC for this section, and we strive to make all decisions and reviews with one month (provided referees respond in a timely manner), and referees will be selected to review not only the topic explored but also the elements of synthesis included. These efforts will be open-access published as editor’s choice to stimulate positive practices in our field more broadly and to facilitate longitudinal cross-study contrasts of ecological syntheses. Ecology is a very diverse discipline, and big-science ecology needs big bridges between our synthetic discoveries. Granda and colleagues’ meta-analysis on the physiological responses of woody plants to extreme climatic conditions was therefore selected as EiC for November. Understanding responses of species to winter cold and summer drought extremes is especially relevant in face of ongoing climate change. The authors compiled the existing literature on these responses of woody plants from temperate zone and show that that deciduous angiosperms were most sensitive to climatic stress and that evergreen species show less pronounced seasonal responses in both leaves and stems than deciduous species.

The October issue has been dedicated to a set of integrative research papers that bring synthesis on the functioning of soil food webs brought together by one of our editors Ulrich Brose. You can read more on this here. We jointly published with this special issue the forum paper of Fabrizio and colleagues as editor’s choice. They provide a concise synthesis on the role of top predators in food webs. Ecological research on the role of top predators in food webs is becoming increasingly important and popular in terrestrial (see for instance Boersma et al) and marine systems (e.g. Goyert et al; Rizzari et al. ) but also from a more theoretical point of view (e.g. Berg et al.). This exponentially expanding literature is, however, strongly associated with a rapid disintegration into specialized, disconnected subfields for study (e.g. vertebrate predators versus invertebrate predators, community ecology versus biological control etc.). The authors argue that this results in a loss of coherent, integrated understating of the role and importance of these species in ecosystems.

You might, sometimes, have heard the phrase ‘everything is connected’. Maybe you are thinking about computers and mobile phones, but in fact this statement is particularly true in nature. For instance, we know that species are not isolated entities, instead they are part of communities in which multiple different species are interacting with each other. Some of these interspecific interactions are cooperative and positive for all interacting partners, and are called mutualistic interactions. Virtually all species on Earth are involved in one or more mutualistic interactions. Specifically, the interactions between plants and their pollinators may be some of the most studied ones, as nearly 85% of plants rely on animals for pollination service. In the last 20 years the study of pollination interactions using network analysis has been a hot topic in ecology. Networks have proven to be a useful tool to unravel patterns in plant-pollinator interactions at the whole community level. Usually, almost all plant-pollinator networks are constructed at the species-level (species-based networks), i.e. nodes in the network are plant and animal species and links represent the interactions occurring between them (e.g. flower visits). However, species are composed of populations of individuals and those individuals are the true actors establishing interactions in nature. Even more interesting is the fact that conspecific individuals are phenotypically and behaviourally diverse with respect to, e.g. size, sex, age, and social status, which also might imply that their foraging decisions become different. Most ecological networks studied to date have not considered this intraspecific variation in interactions, despite the importance of individual variation within natural populations addressed in the theory of evolution by natural selection. For that reason, moving from species-based networks to individual-based networks, to disentangle a process, which can be defined as network downscaling, is probably one of the major challenges right now in ecological network research.

 

Network downscaling. In traditional species-based networks each node represents a species (red nodes are pollinators and green ones are plants), but if we decompose a species into its constituting individuals we can obtain an individual-based network. In the figure, downscaling is only represented for the pollinator subset.

 

In an attempt to fill this gap of knowledge, we got the idea of downscaling an entire pollination network to the individual level for the pollinator subset and explore network patterns at both interacting scales: species and individuals. This was possible with the study of pollen loads of insect individuals. Insect flower visitors in two mountain shrub communities from Mallorca (Balearic Islands) were captured, and later in the laboratory, pollen carried by each one was identified and quantified under the microscope. It was a highly time consuming and difficult task, but it paid well off as it provided a record of the flowering species visited by each individual pollinator over time. Data revealed that generalized species in the plant-pollinator network are composed of specialized and idiosyncratic individuals. The high heterogeneity in individual foraging behaviour and the high individual specialization of pollinators are obviously hidden in traditional species-based networks, and thus determine differences in several topological properties between species-based and individual-based networks. Particularly, the modular structure – a broadly described pattern in pollination networks which consists of densely connected groups or cliques of nodes with sparse connections to other groups– is not consistent across networks at the two scales. We found that modularity increases when downscaling networks to the individual level, and we confirmed this result using different modularity detection algorithms. In contrast to the view of modules as a set of taxonomically related species or species with convergent morphological traits in species-based networks, modules in individual-based networks are groups of functionally different pollinators distantly related but with overlapping pollen niches. Thus, interestingly, conspecific individuals are distributed in different modules. Modules showed to have a strong phenological component, and attributes related to the phenophase of plants and individuals even determined the topological roles of nodes in the network. Only when downscaling to the individual level it was possible to detect a dynamical interaction switching within-species and a module turnover throughout the flowering season, thus modules of individuals assembled and disassembled over time.

Study site. The study was conducted on two locations in Puig Major (1445 m), the highest mountain in Mallorca (Balearic Islands).

Methods. Pollinator observations were conducted in the field. Insects visiting flowers were captured and, later, their pollen loads were analyzed in the lab.

 

In conclusion, findings reported in our study, “Increasing modularity when downscaling networks from species to individuals”  (Tur et al.) highlight that network patterns differed across the individuals and the species scales, because much within-species variation exists. This implies that it is not always possible to deduce structure at one hierarchical level from information about structure at an adjacent level. Combining the study of networks at both scales offers the possibility of uncovering important properties and processes, which might influence network stability, dynamics and the outcomes of interactions.

Distribution of conspecifics into modules. One of the objectives in our study was to investigate whether individual-based networks were modular and if this was true, to analize how conspecific individuals were distributed among modules. There are two possibilities: (a) all conspecific individuals belong to the same module, or alternatively, (b) conspecific individuals belong to different modules. In most species we found ‘b’.

 

Module turnover. When downscaling from species to individuals, a module turnover associated to seasonality was identified, so that at a given moment of the season there is predominance of a particular module of individuals. The complete individual-species network and the different slices of each month are shown in the figure.

By Christina Tur

 

 

Yes, made it through the wallaby attack!, No, no, no- no reason to celebrate Eucalyptus trees. Less marsupial browsing – opens up for more insects. Life is just not easy. Read more in the Early View paper “Direct and indirect effects of marsupial browsing on a foundation tree species” by Christina L. Borzak, Julianne M. O’Reilly-Wapstra and Brad M. Potts. Below is their summary of the study: Herbivores have impacts on plant survival, growth and form and these induced changes can have important flow-on consequences to subsequent organisms. Although a large number of studies in eucalypt systems have previously investigated vertebrate feeding preferences and the direct impacts of herbivory, few studies have focused on how herbivores interact to directly affect each other’s feeding preferences, and even less have addressed the indirect plant-mediated effects of herbivores. We investigated the direct and indirect effects of uncontrolled browsing by marsupial herbivores including the common brushtail possum (Trichosurus vulpecula), Bennetts wallaby (Macropus rufogriseus) and the red-bellied pademelon (Thylogale billardierii), in a Eucalyptus system known to have extended community and ecosystem genetic effects. In a common garden trial containing 525 full-sib Eucalyptus globulus families from an incomplete diallel crossing program located in north-eastern Tasmania, Australia, we assessed the genetic basis to herbivore preferences, the impact of a single and repeated marsupial browsing event on tree fitness and morphological traits and the associated indirect plant-mediated effects on a subsequent herbivore, autumn gum moth (Mnesampela privata).

Autumn gum moth larvae (Mnesampela privita)

Common brushtail possum (Trichosurus vulpecula)

Red-bellied pademelon (Thylogale billardierii)

We found that marsupial browsing was not influenced by plant genetics, but spatial components instead affected the pattern of damage across the trial. Marsupial browsing had significant impacts on tree development, morphology and survival, resulting in reductions in survival, height and basal area, an increase proportion in multiple stems, delays in flowering as well as delays in phase change from juvenile to adult foliage. Fitness impacts were minimal in response to a once-off browsing event, but effects were exacerbated when trees suffered repeated browsing.

Trait assessments under way at the Eucalyptus globulus trial site by authors Christina Borzak (left) and Julianne O’Reilly-Wapstra (right).

Assessments of autumn gum moth damage showed that their presence was linked to marsupial browsing, with browsed plants being less susceptible to the insect herbivore. The majority of the effect was attributed to the indirect effects of browsing on tree height, where AGM were attracted to taller trees that were not browsed. Such indirect effects have the potential to influence biotic community structure on a foundation species host-plant, and the evolutionary interactions that occur between organisms and the host-plant themselves.

Predicting herbivore intensity in disturbed habitats is not as easy as it might seem… Results were a bit surprising in “Land-use legacies and present fire regimes interact to mediate herbivory by altering the neighboring plant community” by Philip G. Hahn and John L. Orrock. Below is the author’s summary of the study:

The southeastern United States was once teaming with biodiversity in the sprawling, open pine savannas that stretched from Virginia to Texas. Post-settlement, these biodiversity hotspots were quickly reduced to less than 3% of their original extent, largely through conversion to agriculture and fire suppression. More recently, many agricultural fields have been abandoned and replanted with pine trees. Although these degraded woodlands harbor low levels of biodiversity, they offer tremendous potential to restore lost species. Particularly, ecologists know very little about interactions among plants and insects in these degraded ecosystems. Hypothetically, insect herbivores, such as grasshoppers, could be suppressing plant diversity in these post-agricultural woodlands by preferentially consuming more palatable remnant wildflowers that attempt to reestablish.

The sun rises over a rare remnant longleaf pine savanna, fueling a motley array of biological interactions.

We tested this idea by transplanting native plants into herbivore exclosures within longleaf pine stands on historic agricultural sites. In order to compare disturbed and undisturbed longleaf pine savannas, we also located several stands of remnant longleaf pine savanna. Because some of these stands experienced woody encroachment due to fire suppression, we crossed fire frequency with historical land use as a component of our experimental design. This created a gradient of degradation with either low or high fire frequency stands within post-agricultural or remnant woodlands.

After measuring herbivore density and herbivory rates on our experimental plants for a field season, we found that sites with low levels of plant cover supported small populations of herbivorous grasshoppers, which resulted in low herbivory rates on our experimental plants. These sites were usually degraded by historic agriculture and were extremely fire suppressed.

Sites representing the range of neighboring plant cover at our experimental sites. Insect exclosures or control cages (with holes) were placed over a set of experimental plants.

 

There were more grasshoppers at sites with extremely high levels of plant cover. Herbivory rates were expected to be higher at these sites because there were so many grasshoppers. As it turns out, herbivory rates were actually low because there were many more neighboring plants for grasshoppers to consume. In other words, high abundance of neighboring plants swamped out the negative effect of herbivory on the focal plants. These sites with low herbivory rates tended to be frequently burned remnant sites, meaning that remnant sites can support high populations of both plants and grasshoppers, while minimizing the negative effects that herbivores have on plants.

We found the greatest herbivory rates at intermediate levels of plant cover, where grasshoppers were also in intermediate abundance. These sites tended to historically be used for agricultural or were fire suppressed remnants. In other words, moderately degraded sites had the highest rates of herbivory.

 

Data being generated

By demonstrating that past and present human activities play a key role in present-day plant-herbivore interactions, our work has several important implications for basic and applied ecology. The findings provide a starting point to predict when and where herbivore density or neighboring plants will be important drivers of herbivory. The results also have implications for the recovery of biodiversity in post-agricultural lands and other systems affected by human disturbance by generating predictions about which habitat types will be more susceptible to herbivores.

Aptly described by the naturalist Arthur-Miles Moss, the life of a caterpillar is a virtual struggle for safety from formidable predators, ruthless parasites, and fatal pathogens. To cope, caterpillars possess an array of anti-predator adaptations, or defenses, which aid them in the struggle. An individual caterpillar might employ camouflage, chemical defenses, hairs, spines, and aggressive behaviors to escape or repel its enemies. Despite the fact that these defenses constitute some of the classic examples of adaption, we still know very little about their effectiveness against predators in a natural community context.

 

The bold, gaudy colors of certain insects have arrested the eye of many a naturalist. Alfred Russel Wallace and Henry Bates, who collected butterflies in the Amazon, proposed an ingenious evolutionary explanation for the flashy appearances of many insects. They argued that conspicuous colors on insects are actually warning signals to would-be predators, such as birds, which advertise underlying chemical defenses. The stronger the signal, the clearer would be the message: “Don’t mess with me, I’m poisonous.” Thorough experimental confirmation of this idea, called aposematism, did not come until the second half of the 20^th century.

Figure 1. Aposematic caterpillar of the monarch butterfly on its milkweed host plant. Photo by Michael S. Singer.

The great Victorian naturalists likewise surmised that camouflage was another important defense of insects against bird predation. Observations of caterpillars, katydids, and walking sticks in their natural environments revealed a wondrous precision in the match between the insect’s appearance and the vegetation upon which it lived. Darwin’s and Wallace’s theory of natural selection was the best scientific explanation: only the best camouflaged individuals of each species would escape detection by predators.

 

Figure 2. Camouflaged inchworm caterpillar on its host plant, manzanita, in southern Arizona. Photo by Michael S. Singer.

 

Over the last 50 years, many additional, important observations and experiments have reinforced these evolutionary theories of prey defense. But the vast majority of experimental studies used captive avian predators or artificial prey (such as dead or artificial insects) exposed to wild birds, leaving some question about the effectiveness of aposematism and camouflage in natural predator-prey interactions, which are notoriously difficult to observe directly in the wild. In the mean time, new techniques and technologies have emerged that allow researchers new modes of studying prey defenses in the wild.

Figure 3. Black-capped chickadee with a captured caterpillar in one of the forest sites used to study bird predation of caterpillars in Connecticut. Photo by Christian Skorik.

 

Enter the new study by Lichter-Marck and colleagues, “The struggle for safety: effectiveness of caterpillar defenses against bird predation.” This study used a bird-exclusion field experiment set in the forests of Connecticut, USA to test evolutionary theories of prey defense in the context of a natural ecological community. Over four years, the research team surrounded hundreds of experimental tree branches with garden-variety bird-proof netting, matching each experimental branch with a control branch lacking netting. The netting was applied at the beginning of each growing season, and allowed caterpillars to come and go while preventing access to insectivorous birds. Three weeks later, the researchers returned to each branch and collected the caterpillars living on them. By experiment’s end, the caterpillar species with the largest proportional increase in numbers in experimental branches (protected from bird predation) relative to control branches (open to bird predation) were inferred to suffer the most bird predation. By measuring the defensive traits of each caterpillar species and correlating them with the inferred magnitude of bird predation, the researchers could determine which traits were most effective as defenses against bird predation.

 

 

Figure 4. Red maple branch covered with a bird-exclusion net, one of the experimental branches used in this study. Photo by Christian Skorik.

 

This unique methodological approach supported the main prediction of aposematism theory: among the 38 species of caterpillars that were numerous enough to analyze, those that possessed warning signals, such as bright coloration, received the most protection from birds. But the study revealed another, critical aspect of the warning strategy of defense: stereotypical resting location. The caterpillar species most protected from birds combined warning signals with highly stereotypical resting locations on the plant. That is, their appearance and their location together provided the warning signal to birds. This finding highlights the relatively neglected behavioral aspect of warning strategy of defense.

 

Figure 5. A warningly-signaled caterpillar species (Nola triquetrana) on its host plant, witch hazel, at one of the forest sites used in this study. Photo by Michael S. Singer.

 

Yet the majority of the 38 caterpillar species did not possess warning signals, instead employing camouflage as their primary defensive strategy. Because visual camouflage can result from several different tricks in appearance (disruptive patterns, countershading, etc.), the magnitude of camouflage can be difficult to measure. The researchers turned to an increasingly used method, the human proxy predator assay. In this assay, human participants were shown digital images of the caterpillar species resting on their host plants, and a computer program was designed to record how quickly each participant located each caterpillar with an accurate click of the mouse. The longer it took, on average, to find a caterpillar species, the greater the magnitude of camouflage was inferred.

 

Figure 6. A camouflaged caterpillar species (Catocala ultronia) on its host plant, black cherry, at one of the forest sites used in this study. Photo by Michael S. Singer.

 

In support of evolutionary theory of prey defense, the study found that the caterpillar species with the greatest inferred magnitudes of camouflage received the most protection from birds. Once again, this part of the study revealed a behavioral twist. A caterpillar species’ frequency of behavioral responsiveness to attack, measured independently, worked against the effectiveness of camouflage. This finding suggests that effective camouflage requires not only an appearance that matches the prey’s background, but also behavioral maintenance of the cryptic posture in the face of physical disturbance.

The authors, through Michael S. Singer

While most people know the aboveground part of forest ecosystems, very few have caught a glimpse of the belowground environment that comprises a highly diverse fauna. The number of species co-occurring on less than a square meter habitat ground (or a cubic meter of habitat volume) exceeds that of the aboveground compartment by far. In consequence, forest soil communities have been called “poor man’s rainforest”. Nevertheless, we still do not know much about the animals living in these “next-door” habitats and the structure of their communities.

Impression of a central European beech forest. Much more is known about the aboveground animals and their interactions than about the belowground communities that carry out the critically important ecosystem functions of litter decomposition and nutrient recycling.

 

Why is our knowledge about forest soil communities so limited? Progress in our understanding of soil communities and processes has been hampered by the chronic lack of data for complex soil food webs of high resolution. This is caused by aggregation of populations in coarse functional groups, whose species often span multiple trophic levels from primary to secondary or tertiary predators. In addition, soil is an opaque medium leading to a limited visibility of interactions. Further, detritivores typically ingest a multitude of intermingled resources hampering identification of what the animals actually digest and live on. In the recent years, new molecular methods have emerged providing the possibility to unravel belowground interactions and the complex structure of forest soil food webs.

 

A soil core provides an impression of the complex structure of the belowground habitat. This environment comprises a highly diverse and complex animal community spanning several trophic levels.

The special issue “Into darkness” comprises several studies of central European beech forest soil communities. The studies included in this special feature fill employ state-of-the-art methods to unravel general feeding guilds by stable isotopes (Klarner et al.) as well as specific directed feeding interactions by molecular gut content and fatty-acid analyses (Ferlian and Scheu, Günther et al., Heidemann et al.). This allowed the construction of the first highly-resolved complex soil food webs (Digel et al.) and analyses how they respond to external drivers such as the nutrient stoichiometry of the basal litter (Ott et al.) and climate change (Lang et al.). Together, they provide a unique impression of a voyage into darkness.

Ulrich Brose, Editor of the Oikos Issue “Into Darkness”

 

 

Grasshoppers tend to increase in abundance during drought, no decree, or increase…Find out which and when in the Earl View Oikos paper “Water stress in grasslands: dynamic responses of plants and insect herbivores” by Paul A. Lenhart and co-workers. Below is their summary of the study:

When I first saw the climate projections from NOAA in 2011 that there would be a severe La Niña-fueled drought I was worried that my fieldwork season would be a bust. In 2011, Texas, as well as much of the south central United States of America, suffered through the worst seasonal drought since modern record keeping began in 1895. The drought had severe economic and ecological impacts across the region, but I was focused on my main study organism: grasshoppers. These insects are a very important component of grassland ecosystems, and for the past two years I, together with my co-supervisors (Micky Eubanks and Spencer Behmer), had worked in the grasslands and savannah of central Texas studying a vibrant grasshopper community, consisting of over 56 species. I was working to understand the diet breadth of some of the key species, including their macronutrient regulation behavior, while also quantifying competitive dynamics between these species.

 

Examples of grasshopper diversity. Clockwise from the top left: Melanoplus packardii, Hadrotettix trifasciatus, Acrolophitus hirtipes, Phaulotettix eurycercus.

 

Prior to 2011, one of our sampling seasons (2009) was slightly drier and we found a decrease in grasshopper density and abundance. This went against many previously published observations of grasshoppers and other insect herbivores having larger populations in drier years. The proposed mechanism in the literature is that plant nutrient content actually increases with water stress. However, studies that measure the effect of water stress on plant nutrients typically use greenhouse-reared plants or crop species, and generally measure plant quality as simply a function of nitrogen content. We now know that plant dietary quality is much more complex, and in particular that herbivores actively regulate their protein and carbohydrate intake. Therefore, we decided to change course from our originally planed competition experiment. Instead, we took advantage of the coming drought to conduct a manipulative study in order to gain insights into what happens to native plants, and herbivore behavior, when the rains do not come

            We started our experiment early enough in the season to quantify, over time, the effect of water stress on the native grassland plant’s quality, quantity, and diversity. We marked off small open plots distributed across the grasslands of the Balcones Canyonlands National Wildlife Refuge. Half of these plants were left alone to suffer through the drought and we watered the other half [laboriously] by hand to mimic average summer rainfall. We did this through the growing season and took plant samples and visual grasshopper surveys monthly; in each plot individual grasshoppers were identified to species by sight. After completing each grasshopper survey, we measured grass and forb species richness, and took samples back to the lab to assess biomass and macronutrient content. Specifically, we quantified both digestible protein and nonstructural carbohydrate content in bulk samples of grass and forb tissues using biochemical assays.

 

Behind the scenes of watering plots by hand in the field.

 

            At the end of the summer we found that drought reduced grasshopper abundance and diversity, relative to our water supplemented plots. Using our knowledge of different grasshopper species diets, we grouped species into functional feeding groups and found that functional groups responded differently to our watering treatments. Forb specialists seemed unaffected by the drought while grass-feeders and mixed-feeders (grass+forbs) were significantly less numerous in the unwatered plots. These different grasshopper responses were due to their particular feeding biology and the fact that grass and forbs responded differently to water stress. We go into more detail in the manuscript, but in short, forbs decreased in diversity and experienced a significant shift in their macronutrient profile over time, becoming less protein biased. In contrast, grass biomass was reduced by water stress, but grass protein-carbohydrate content was similar between our two water treatments.

 

A freshly watered plot in a parched grassland.

 

Our results are significant because we used naturally-growing, drought acclimated plants, and quantified protein-carbohydrate content – which are the two most important nutrients that affect insect herbivore feeding behavior and performance. Our research provides valuable data on how plant macronutrient content, biomass, and diversity co-vary in the field, and such data can be used to parameterize models that can help us better understand how generalist herbivores forage and perform under drought conditions, which are predicted to become more common as climate change intensifies. Although more work is required, we envision the use of remote sensing technology, measuring plant quality, biomass, and diversity, to better manage insect pests in rangeland ecosystems.

 

Mixed-grass oak savannah on the Balcones Canyonlands National Wildlife Refuge during a wet summer.

Ecological networks quantify the diversity of direct and indirect interactions taking place in nature. However, due to their complexity, ecologists rely heavily on the use of metrics to summarize aspects of network structure thought to be of biological importance. Many of these structural features are non-random and strongly conserved across diverse habitats and species assemblages, begging the question: what factors determine network structure? The most successful hypotheses to explain these patterns are the neutrality and biological constraints hypotheses, which posit that species interactions can be explained by trait mismatches, and relative abundances respectively. In the Early View paper “Species traits and relative abundances predict metrics of plant-pollinator network structure, but not pairwise interactions” in Oikos, we Colin Olito and Jeremy W. Fox, evaluate the relative ability of trait-based and neutral models of species interactions to explain the structure of a temporally resolved alpine plant-pollinator visitation network.

 

An unidentified muscid visiting Erigeron peregrinus. Although their charm often goes unappreciated, flies are by far the most diverse and abundant pollinators in the alpine. Interestingly, many of their behaviours that facilitate pollination differ markedly from more intensively studied foraging pollinators, such as bumblebees. Understanding their crucial role in alpine and high-latitude plant-pollinator communities will require a greater understanding of both their reproductive and foraging biology. Photo credit: Martin Fees.

As our title suggests, species traits and relative abundances successfully predicted every metric of network structure tested, but failed to predict observed interactions. That is, a variety of models can predict network metrics well, but for the wrong reasons. We explore the implications of this contrast, and highlight potential problems with the use and interpretation of network metrics. We also found that species phenologies (the timing of flowering or pollinator activity) always out-performed neutral models at predicting pairwise interactions, and discuss limitations of neutral models of network structure, particularly when species interactions are under-sampled. We suggest that future progress in explaining the structure and dynamics of ecological networks will require new approaches that emphasize accurate prediction of species interactions rather than network metrics, and better reflect the biology underlying species interactions.

Sampling plant-pollinator interactions in a low-alpine meadow in Kananaskis Country, Alberta, Canada. Photo credit: Martin Fees.

Bat acoustic signals might seem rather simple. yet, there are individual differences. The background to these variations are studied in the Early View paper “Geographical variation in echolocation vocalizations of the Himalayan leaf-nosed bat: contribution of morphological variation and cultural drift” by Aiquing Lin and co-workers. below is their summary of the study:

Animals’ acoustic signals often vary geographically—but how and why? We studied the geographical variation in echolocation vocalizations of a widespread bat species Hipposideros armiger sampled from 17 localities in South China. We asked whether there was detectable population divergence in the vocalizations and whether the acoustic divergence was related to the variation in morphological (forearm length), climatic (mean annual temperature, mean annual relative humidity, and mean annual precipitable water), geographical (latitude, longitude, elevation, and geographical distance), or genetic (genetic distance and population genetic structure) factors. We found remarkable geographical variation in the peak frequency of echolocation pulses of H. armiger, which clustered into three groups: Eastern and Western China, Hainan, and Southern Yunnan. The acoustic divergence was significantly related to morphological differences and geographical distance, but not significantly related to climatic (after controlling for morphological distance) or genetic variation. We also found a correlation between population differences in morphology and climatic variation (mean annual temperature). Our results suggest the action of both indirect ecological selection and cultural drift promote divergence in echolocation vocalizations of individuals within geographically distributed populations.

Figure 1 Himalayan leaf-nosed bat (Hipposideros armiger)

 

 

Figure 2 Oscillogram (above) and Spectrogram (below) of an echolocation pulse of Hipposideros armiger. fpeak = peak frequency.

Male of the harvestmen Zygopachylus albomarginis (with yellow ink marks) inside his mud nest, while a female approaches from the outside [Credit: Gustavo S. Requena]

Nests are extremely important for males’ fitness when reproduction and parental care are associated with these structures. The possession of a nest and its conditions may determine male attractiveness (due to female reproductive decisions) and offspring survival (due to protection against adverse biotic and abiotic conditions). Nest construction and maintenance, however, may also impose costs to males: nest-related behaviors may demand time and energy or may increase mortality risks. The costs and benefits approach is usually used to understand the evolution and maintenance of behavioral traits, and we explored this framework in a study with the Neotropical harvestmen Zygopachylus albomarginis.

 

During the breeding season, nesting males of Z. albomarginis spend several months building, repairing, cleaning and defending their mud nests. After mating, females abandon the eggs under the protection of males, who actively defend them against predators and fungal infection. Although nest defense, nest maintenance, and offspring protection contribute to different components of males’ fitness, they are performed concomitantly and entail similar behaviors. For instance, when a nesting male chases away a conspecific individual, he defends the possession of his nest at the same time he protects the offspring against a potential egg predator (see video below). Moreover, nest maintenance requires males to remove debris and prevent fungal growth inside the nest, actions that also contribute to protect eggs against infection.

 

VIDEO: [Credit: Gustavo S. Requena]

 

In our Early View Paper “Lack of costs associated with nest-related behaviors in an arachnid with exclusive paternal care”, we quantified the costs of nest-related behaviors in Z. albomarginis under natural conditions. Because males are mainly constrained to forage in a small area close to the nest for up to five months, we expected high energetic costs of being associated with a nest. However, we did not find any evidence of decline in the physical conditions of nesting males over time. Interestingly, males may spend several days eating fungal hyphae growing inside their nests, which we suggest constitutes an important food resource to stationary individuals and compensates for energetically costly activities performed for so long periods.

 

 

At the left, we can see a male inside his nest on a fallen trunk without fungus infestation. At the right, the trunk is covered by fungus fruiting bodies, except inside the nest. Nest-cleaning behavior maintains hygienic conditions inside the nest at the same time it provides food to the male, which feed upon the fungus hyphae. [Credit: Gustavo S. Requena]

 

Due to contest injuries over the possession of a nest or its conspicuousness, we also expected high mortality risks associated with nest-related behaviors. The survival probabilities of stationary nesting males, however, were higher than the probabilities of vagrant individuals not associated with nests surviving. This pattern of differential mortality dependent on Z. albomarginis movement activity may be explained by the potential higher chances of encountering predators while moving, particularly walking among trees and crossing the leaf litter.

 

Given that females lay eggs exclusively inside nests and the costs of nest maintenance and defense are extremely low (if not absent), the million dollars question is “why do not all males have a nest?” Males add salivary secretions to the mud at the moment they build the nests. One possibility, therefore, is that the production of such secretion is costly and only males in good body condition would be able to invest in nest construction. Although the costs of performing this activity was not evaluated in our study, the fact that vagrant males may occupy an empty nest or even aggressively attack a nesting male and take over his nest suggests that some individuals rely on usurpation as an alternative reproductive tactic to acquire nests.

 

 

Male resting inside his nest, which contains several black eggs (indicating advanced embryonic development) [Credit: Gustavo S. Requena]

The authors through Gustavo S Requena

What happens when climate change destroys too many habitats? In the Early View paper “Robustness of mutualistic networks under phenological change and habitat destruction” Tomás A Revilla and co-workers present a model predicting potential outcomes.

Below is a short summary of their model and paper:

There is concern that climate change will disrupt the temporal schedules of interactions between plants and their pollinators or seed dispersers. This can make communities vulnerable to other ecological threats, for example habitat destruction. In our paper “Robustness of mutualistic networks under phenological change and habitat destruction”, we studied the simultaneous effects of phenological shifts and habitat destruction on the diversity and structure of mutualistic metacommunities.

We created a spatially-explicit model, in which the network of mutualistic interactions is locally determined by species occupancies, over a finite number of randomly distributed sites. The strengths of the interactions depend on the amount of phenological overlap between the species, affecting local survival. Our model uses empirical data on plant and pollinator phenologies recorded a century ago by Charles Robertson, and in present times and in the same area by Burkle et al (DOI: 10.1126/science.1232728), giving us the opportunity to simulate projected as well as historical changes in phenology. Habitat destruction was simulated by removing sites from the model.

Interactions depend on local species presences and phenological overlaps (in days). Extinctions are caused by site destruction (X) and interaction weakening, e.g. pollinator 1 becomes disconnected and plant 2 losses many interaction-days.

Our results show that habitat destruction causes the gradual erosion of local diversity. A catastrophic collapse in global diversity finally happens when the number of non-destroyed sites becomes too low, and the distances between them too large for recolonization. Recovering from such collapses could be difficult due to the positive feedbacks characterizing mutualisms, which promote alternative stable states.

Under phenological shifts interactions become weaker on average, increasing local extinction rates. When habitat destruction and phenological shifts occur together, they act synergistically: many sites become barren even though they are not destroyed, but for practical purposes these sites behave as if they were destroyed, making metacommunities even more vulnerable to habitat destruction.

Decrease in local and global diversity in response to habitat destruction, for 0, 10, 20 and 30 days of average advance in species phenologies.

Previous research has shown that connectance and nestedness can make mutualistic communities robust against cascading extinctions. We discovered that in effect, these network properties gradually decline with habitat destruction, leaving a very small core of highly connected sites holding the metacommunity before the final collapse. Small alterations in phenology can raise connectance a little bit, due to a few generalist species being able to make new interactions, but overall, large alterations tend to reduce connectance.

We can conclude that the robustness of mutualistic metacommunities against habitat destruction can be greatly impaired by the weakening of mutualistic benefits caused by the loss of phenological overlap.

Image credits: Michel Loreau

We wish to thank Jacob Johansson, Niclas Jonzén and Jan-Åke Nilsson for inviting us to contribute with our paper to the special issue about “Phenological change and ecological interactions”.

Many animals locate resources and orient in rather complex environments like vegetation, coral reefs or leaf litter. How does the presence of a stimulus affect animal movement in such complex environments? And what is the relative contribution of a stimulus vs. the complexity of the environment on animal movements? Find out in the Early View paper “Relative roles of resource stimulus and vegetation architecture on the paths of flies foraging for fruit” by Oriol Verdeny-Vilalta and co-workers.

Below is the author’s summary of the study:

To answer the questions above, we developed a novel method using random walks on graphs to accurately estimate both the perceptual range and the attraction strength from 3D movement trajectories of individuals. The perceptual range gives us an idea of the maximal distance at which a stimulus source biases the movement. The attraction strength measures how the attraction of the stimulus varies at different distances within the perceptual range. Additionally, the methodology enabled us to calculate the relative roles of the architecture of vegetation and of the strength of attraction of a stimulus on the movement of individuals. We applied the methodology to estimate perceptual range and strength of apple maggot flies (Rhagoletis pomonella) foraging for artificial fruit in apple trees of varying complexity.

 

Figure: Main steps (a-d) followed to study animal orientation in complex vegetation structures.

 

In our study we have shown that, conditional on visiting the stimulus location, the presence of the fruit affects animal movement much more than the plant architecture. Moreover, we found that plant complexity makes a minor contribution to defining the perceptual range, but a large contribution to the attraction strength. Thus, we highlight the importance of estimating not only the perceptual range but also the attraction strength of animals, which has been traditionally neglected. Our findings have implications for studying foraging ecology and landscape connectivity. For example, several dispersal models developed to study landscape connectivity incorporate the perceptual range of individuals, but the distinction between perceptual range and attraction strength is still lacking. We expect that landscape connectivity will be higher in animals showing higher attraction strengths for equal perceptual ranges. Given that animals use their sensory systems to make informed decisions and that they move and interact in heterogeneous environments, our approach might be of relevance to the myriad of animals walking and searching in complex environmental structures.

When habitat is lost so are species. One way of investigating the processes underlying this pattern is to pay attention to the identity (not only the number) of species. What happens to between-site differences in species composition when habitat loss transforms formerly continuous habitat into habitat fragments?

Who consults widely applied theoretical frameworks (e.g. theory of island biogeography) to answer this question will come to the conclusion that between-site differences in species composition – i.e. beta-diversity – should increase following habitat loss due to a strong influence of chance on the extinction process. Species are assumed to be ecologically equivalent (all have the same chance of getting extinct) and ecological drift (stochastic changes is species abundance) to increase in importance when populations are small. Further, chance makes it unlikely that populations surviving in different habitat remnants belong to the same species, and homogenization is hindered by isolation.

Who, on the other hand, consults empirical work will find that for various groups of plants and animals it is common to observe that, of the diverse set of species in continuous habitats, it is frequently the same small set of species that persists after habitat loss. Apparently, only certain resistant species are able to survive in fragments, thereby making the species composition in fragments deterministically more (and not less) similar, indicating – in contrast to theoretical models – low influence of chance on species extinction.

In our study “Ecological filtering or random extinction? Beta-diversity patterns and the importance of niche-based and neutral processes following habitat loss “ we investigated how the importance of different processes changes with habitat loss relying on a large database of small mammals in the Brazilian Atlantic Forest. We used a null model approach to quantify beta-diversity and make inferences about the relative importance of niche-based (deterministic) and neutral (stochastic) processes on community assembly at landscapes with varying degree of habitat loss.

Our results did not support a positive relationship between beta-diversity and habitat loss, as predicted by commonly-used theoretical frameworks. Rather, when considering exclusively species composition (disregarding their abundance), beta-diversity was independent from habitat loss, with small mammal communities being more similar than expected by chance in deforested as well as continuously-forested landscapes. However, when species abundance was taken into consideration, we observed a drastic decrease in beta-diversity with habitat loss (i.e. biotic homogenization), thereby indicating an increase (rather than a decrease) in the importance of deterministic processes at landscapes with high degrees of habitat loss. Finally, we observed a drastic change in species composition in a highly deforested landscape, with communities being not just a rarefied sample but rather disproportionately dissimilar to the communities in continuously-forested landscapes.

These results indicate that habitat loss can be seen as a strong ecological filter and species extinction is clearly more influenced by deterministic than by stochastic processes. Against this background, the incorporation of relevant species traits into theoretical models seems to be a useful step forward for the practical relevance of these models. Moreover, pro-active measures seem to be essential to prevent tropical landscapes to go beyond critical levels of habitat loss.

The authors through Thomas Püttker

Understanding lifetime tracks and fitness of long distance avian migrants. This is the title of our DFG-funded German-Israeli Project Cooperation and it is also our quest for several years. Within this project, we aim to explore how movement, survival and reproduction reflect an optimal response to the environment. Evidence is drawn from both theoretical and empirical analyses. Migrants like white storks are particularly interesting for studying these questions as they move large distances and may experience different environmental conditions in different parts of the world with more or less strong impacts on their fitness (carry-over effects). Small-scale movement and behavior and their impact on local population dynamics are equally interesting. Latest technologies allow us unprecedented insights into the life of animals. For example, ultra-light GPS tags allow tracking individuals with very high temporal resolution and over several years, and acceleration measurements allow classifying behavior from distinct acceleration signals. These data together with careful monitoring provide the means for better understanding movement phenomena and their consequences for population dynamics and fitness. 

My main focus within the project are developing behavior-based models for different life-cycle stages (e.g. breeding, migrating, wintering) as well as annual-cycle models that allow studying carry-over effects on individual fitness and population dynamics. Thereby, optimality is an important topic. From evolutionary perspective, fitness-maximizing, optimal behavioral strategies should evolve, determining for example when an individual should start reproducing or start migrating within the annual cycle. On finer temporal and spatial resolution, optimal foraging strategies should evolve which are the focus of our study ‚Individual-based modeling of resource competition to predict density-dependent population dynamics: a case study with white storks‘ (Zurell et al.). Here, we aimed to better understand how density-dependent demographic rates may evolve from home range behavior. To this end, we built an individual-based model for foraging white storks that incorporates both physiology and behavior. We expected that the form of density dependence may differ between different home range behaviors. To our surprise, we also found that it may differ strongly between landscapes with the same degree of fragmentation and the same overall resource availability. This phenomenon is strongly affected by the behavioral trade-offs and by imperfect detection of resources. Thereby, simulated patterns corresponded surprisingly well to empirical patterns although the model was not calibrated. For predicting population or even community dynamics under changing environmental conditions, it seems crucial to better understand these interactive effects of behavior and local environment.

We heartily invite you to play around with the model code (available at http://www.wsl.ch/info/mitarbeitende/zurell/downloads_EN) and adapt it to your needs. As you will see, the model also allows exploring additional aspects of movement ecology, for example studying movement paths or density-dependent home range structures in more detail.

How can viruses alter the behavior of the hosts? And to what effect? Find out in the Oikos Early View paper “Virus infection alters the predatory behavior of an omnivorous vector” by Candice A Stafford-Banks and colleagues. If you click on the link below, they will tell you all about it in a short presentation.

 

Oikos presentation Stafford-Banks

If invaders do better by early arrival and growing, will native species also benefit from being early? Not necessarily, as found in the Early View paper “Priority effects vary with species identity and origin in an experiment varying the timing of seed arrival” by Elsa E. Cleland and co-workers. Below is their summary of the study and a photo of the students helping out with field work.

Studies show that exotic species differ in phenology (i.e. are active at different times in the season) from the native species in the communities they invade. In Southern California many of our common invaders are exotic annual grasses and forbs that germinate earlier with the onset of winter rains than native herbaceous species. Hence, exotic species might benefit from emerging earlier in the season, allowing them to pre-empt space and other resources to suppress later emerging species, a kind of seasonal priority effect. We tested this hypothesis in an experiment varying the “arrival” time of pairs of species, by placing seeds of focal species into pots of field-collected soil either simultaneously or one week apart. In contrast to our expectations, native species benefited from earlier arrival more often than exotic species. An important implication of this finding is that giving native species a long “head start” likely aids in ecological restoration efforts.

Then, if being active early is so beneficial, why don’t native species have earlier phenology? Isn’t there sufficient selective pressure to favor earlier phenology in native species? Two additional aspects of our experiment support this idea. First, our results show that different species have various strength and even direction of priority effects. In diverse communities where the identity of neighbors will differ among individuals in the population, this could dampen directional selection on phenology. Second, we found that no significant disadvantage to arriving later when compared to being planted at the same time as a competitor. Thus, for native species that tend to have later emergence time than exotic competitors, there seem not to earlier emergence, as this still exposes them to similar levels of competition.

A final aspect of our experiment that is noteworthy; it was planted and harvested by 36 students enrolled in an undergraduate Ecology Lab course at the University of California, San Diego taught by the lead author (the co-authors on this manuscript were the Teaching Assistants for the course). Teaching evaluations and surveys showed that the students enjoyed contributing to original research, and the amount of preparation and oversight necessary to ensure data quality was not much greater than for any of the other lab activities where data were not destined for publication; a clear “win-win” for both the faculty and the students. Hence, our results demonstrate the synergies can arise by merging undergraduate teaching with faculty research programs.

Undergraduate students contributed to this study by aiding in both planting and harvesting. Here they are shown planting seeds for species pairs at the start of the experiment.

 

How pollinator decline affect plant-plant interactions for pollinator is studied in the Early View article ‘Experimental reduction of pollinator visitation modifies plant-plant interactions for pollination’ by Amparo Lázaro and co-workers.

Several studies have indicated a widespread pollinator decline, caused mainly by land-use changes, degradation of natural habitats, fragmentation and habitat loss. Since the majority of plant species are dependent on animal pollination for reproduction, pollinator decline may influence plant reproduction and the persistence of plant populations. However, a pollinator decline may also affect the way plants interact for pollination because these interactions depend on the abundance of plants and pollinators in the community.

To simulate a pollinator decline we set up a novel experiment to reduce pollinator visitation in two communities (one lowland and one alpine) in Southern Norway (see also Lundgren et al. 2013). In the experiment we compared control plots with plots where pollinator visitation had been reduced by means of dome-shaped cages constructed by bending two PVC-tubes diagonally and covering them with fishnet. The fishnet was totally transparent, so flowers were fully visible from outside the net. In order to allow flower visitors inside cages to exit easily, we left an opening between the mesh and the ground, and another opening in the top of the dome. This experiment effectively reduced pollinator visitation without modifying the composition or behaviour of pollinators, or other important biotic and abiotic variables.

Alpine

Lowland

Lázaro et al. (2014) shows that the reduction in pollinators modified plant-plant interactions for pollination in all the six species studied; although for two of them these interactions did not affect seed set. Pollen limitation and seed set data showed that the reduction of pollinator visits most frequently resulted in novel and/or stronger interactions between plants in the experimental plots that did not occur in the controls. Although the responses were species-specific, there was a tendency for increasing facilitative interactions with conspecific neighbours in experimental plots where pollinator availability was reduced. Heterospecifics only influenced pollination and fecundity in species in the alpine community and in the experimental plots, where they competed with the focal species for pollination. The patterns observed for visitation rates differed from those for fecundity, with more significant interactions between plants in the controls in both communities. This study warns against the exclusive use of visitation data to interpret plant-plant interactions for pollination, and helps to understand how plant aggregations may buffer or intensify the effects of a pollinator loss on plant fitness.

What happens with plants, microbes and animals during soli transition from mull to mor? Find out in the Early View paper “Coordination of aboveground and belowground responses to local-scale soil fertility differences between two contrasting Jamaican rain forest types” by David Wardle and colleagues. below is their summary of the study:

There is much interest in understanding how long term decline in soil fertility, in the absence of major disturbance, drives ecological processes, or ‘ecosystem retrogression’. However, there are few well–characterized systems for exploring this phenomenon in the tropics. We studied two types of montane rain forest in the Blue Mountains of Jamaica that occur in patches adjacent to each other and represent distinct stages in ecosystem development, i.e., an early stage with shallow organic matter (‘mull’ stage) and a late stage with deep organic matter (‘mor’ stage). We measured responses of soil fertility and plant, soil microbial and nematode communities to the transition from mull to mor, and assessed whether these responses were coupled. For soil abiotic properties, we found this transition led to declining soil nitrogen and phosphorus, and reduced availability of phosphorus relative to nitrogen; this led to a shorter and less diverse forest. The resulting litter from the plant community entering the soil subsystem contained less nitrogen and phosphorus, resulting in poorer quality litter entering the soil. We also found impairment of soil microbes (but not nematodes) and an increasing role of fungi relative to bacteria during the transition. These results show that retrogression phenomena involving increasing nutrient (notably phosphorus) limitation can be important drivers in tropical systems, and are likely to involve aboveground–belowground feedbacks whereby plants produce litter that is less nutritious, impairing soil microbial processes and thus reducing the release of nutrients from the soil needed for plant growth. This type of feedback between plants and the soil may serve as major though often overlooked drivers of long term environmental change.

Pictures: Characteristic ‘mull’ forest (top left) and uppermost soil layer with significant mixing of organic material and mineral soil (bottom left); and characteristic ‘mor’ forest (top right) with uppermost soil layer consisting of a thick layer of organic matter (bottom right). Over time the ‘mull’ soil transitions to ‘mor soil’, characterized by less available nutrients and reduced availability of nitrogen relative to phosphorus; this in turn has important consequences for the vegetation and quality of litter that is returned to the soil.

 

 

A slug feeding on capsules of the Rough-stalked Feather-moss (Brachythecium rutabulum).

 

 

Herbivores can increase diversity in plant communities by consuming biomass and reducing light competition, thereby benefitting low growing species such as mosses and liverworts (bryophytes). Slugs and snails are important herbivores of forb species and might promote bryophyte diversity if they reduce forb abundance. They also feed on bryophyte capsules, which contain the spores, and it has recently been shown that these spores, can survive the digestive tracts of slugs and snails (endozoochory: internal transport of propagules). Slugs might therefore benefit bryophytes by dispersing their spores.

 

Moss protonema germinated from slug feces in a previous lab experiment (for details see Boch et al. 2013. Fern and bryophyte endozoochory by slugs. Oecologia 172: 817–822).

 

However, whether gastropod herbivory can reduce the dominance of vascular plants and thereby promote the germination and establishment of endozoochorously dispersed bryophyte spores has never been tested experimentally. Moreover, it is unclear whether these possible interacting effects can influence bryophyte species richness. In our study, “Endozoochory by slugs can increase bryophyte establishment and species richness” (Boch et al.) we tested for endozoochorous spore dispersal by slugs (Spanish slug; Arion vulgaris Moquin-Tandon; Arionidae), in combination with sowing of vascular plants, in a fully factorial common garden experiment. We built 30 slug enclosures of 100 cm × 20 cm and introduced either slugs previously fed with the sporophytes of 12 bryophyte taxa, control slugs previously fed with lettuce, or no slugs. We also sowed seeds of vascular plants into half of the enclosures.

 

Experimental setup in the Botanical Garden of Bern with helpers estimating cover values of bryophytes, herbs, and grasses, which then have been averaged for analysis.

 

Twenty-one days later bryophyte cover was on average 2.8 times higher (3.9% versus 1.4%) in the enclosures containing slugs previously fed with bryophytes than in the other treatments. After eight months slugs had substantially increased bryophyte species richness: there were 2.6 times more bryophyte species in the enclosures which had contained the slugs fed with bryophytes than in the other treatments. Sowing vascular plants into the cages did not affect the initial recruitment of bryophytes but after eight months high vascular plant cover did reduce bryophyte diversity. Our findings suggest that slugs are important dispersal vectors for bryophytes and that they can locally increase bryophyte populations and diversity through dispersing spores. They may also act to maintain bryophyte diversity by reducing the dominance of vascular plants.

What is it that determines if a bird should deposit a seed from a fruit in a specific place or not? I the Early View paper “Seed dispersal in heterogeneous landscapes: linking field observations with spatially explicit models”, Jessica E Lavabre ad colleagues combines modelling with empirical studies to find out! Below is the author’s summary of the study.

Frugivorous birds play a critical role in the population dynamics of many fleshy-fruited plants by defining the template for the establishment of new individuals. Because successful germination and subsequent seedling survival is highly dependent upon the micro-habitat where a seed arrives, it is crucial to understand which factors drive seed deposition. In our study, we aimed to take an important step forward in understanding the complex mechanisms that generate the spatial patterns of seed dispersal. Few studies have previously modelled seed dispersal in a real landscape, mostly because real vegetation structure is often highly heterogeneous. Here, we have taken advantage of a simple study system to parametrize mechanistic seed-dispersal models with empirical field data, and we built three models that test three seed-dispersal predictors: distance from the source tree, microhabitat type, and a combination of both distance from the source and microhabitat type.

To our greatest surprise, the third model, combining distance and microhabitat type, did not perform significantly better than the other two, simpler models. Additionally, our results suggested that what we had initially considered as one population could instead be two functionally distinct patches, with distinct seed dispersal dynamics. Altogether, these results reinforce the hypothesis that functionally distinct groups of frugivore species generate scale specific seed rain patterns.

A sexual reproduction system should confer higher mutation rates and hence evolutionary rate than asexual ones. Is it really so? Find out in the Early View paper “Asexual plants change just as often and just as fast as do sexual plants when introduced to a new range” by Rhiannon L. Dalrymple and colleagues. Below is their summary of the study:

Many of the world’s most invasive plant species can reproduce asexually. However, asexuality might be a double edged sword for introduced species. Shortly after introduction, asexual species might have the upper hand because they do not need a partner for promptly increasing in numbers and establishing populations in the new range. Classic theory tells us that sexual reproduction should fuel the processes of adaption through the creation of variation on which natural selection can act. While asexuality may be of advantage in the early phases of introduction, it may lead to an evolutionary dead end.

We measured the rate of changes in multiple asexual species distributed through Australia’s east coast and New Zealand. We have provided evidence that multiple asexual species have undergone rapid morphological changes in response to the novel environments in their introduced range. We then compared the proportion of asexual species that demonstrated a significant change in at least one trait, and the rates at which these changes progressed, to comparable data on sexual species. This was the first test of the difference in potential for rapid change afforded by sexuality, cross species and in the natural world. Our results were astounding: we found no significant difference in the rate or frequency of rapid changes between asexual and sexual species. That is, sex and genetic recombination do not increase the rate or potential for change in this context. Introduction to a novel environment, a population may experience strong selective forces. The new environmental conditions force rapid and significant changes in the phenotype of both asexual and sexual species. It appears that in the process of introduction – it may be adapt or fail, regardless of breeding system.

The most exciting aspect of this study “Increase of fast nutrient cycling in grassland microcosms through insect herbivory depends on plant functional composition and species diversity” (Nitschke et al)- for me – was to take our experiences and results from the field site – the Jena Experiment that was designed for elucidating mechanisms of diversity effects – and to incorporate them into a microcosm experiment under well controlled conditions.

Here, we aimed at tracking the way of nutrients from the intact plant, over an insect herbivore and its feeding characteristics, into the soil, and over to another trophic level – And to judge the role of plant diversity and functional composition along that way.

• Some aspects of the course showed very clearly (e.g. the release of nutrients with feeding and the relevance of the plant functional groups),
• some were surprising (e.g. both throughfall pH and P increased with herbivory intensity and faeces accumulation – diversity having a similar effects, although independently of herbivore intensity),
• and yet others were challenging (e.g. clear soil microbial responses only occurred at high levels of herbivory).

Finally, stepping back a little and taking our field site results into account, formed a broader picture and gave some new perspectives.

Besides the change of perspective the study brought about and the various methods we applied, it was very inspiring and rewarding to work together in a team of people that have realized quite different niches within Biodiversity Ecosystem Functioning-space.

Fig.1 grasshopper rearing

Fig.2 Chorthippus parallelus as model herbivore

Fig.3 plant communities in mesocosm set-ups

Fig.4 growing seedlings for plant communities

Fig.5 mesocosm and sprinkling device

 

Synthesis and integration are critical elements of knowledge synthesis. Using/reusing the work we have already done is a sign of maturation as a discipline, and a very positive step forward to accelerate inquiry by identifying research gaps, opportunities, and effectively summarizing the strength of evidence to date. We are not only poised for potentially profound novel tests of ideas in ecology, evolution, and environmental science, but we are collaborating in news ways, sharing datasets more freely, and more transparently sharing workflows and insights. Oikos supports this movement in all the ways that we can for now and hopefully even more dramatically as we evolve too.  Hence, we are launching a new formal synthesis section for publications.

Meta-analyses and systematic reviews are but two forms of synthesis. Nonetheless, these reviews are currently the most easily aligned with the traditional peer-reviewed ‘publication’ as paper model. This is admittedly a small step, but we need these contributions to inform evidence-based decisions not just for additional research but for management and application. We now have a section devoted to reviews that include quantitative summaries of evidence from within studies or aggregated datasets, i.e. include effect size estimates and appropriate statistics, and also includes systematic reviews that summarize the state of the art of research for a sub-discipline or topic at the scale of studies (i.e. attributes associated with the research, similar to the meta-data of the datasets but without the data from each study listed). We recognize there are many other forms of synthesis that we need to share, and consequently, we will work hard to ensure that we consider these contributions as well (i.e. how to effectively synthesize evidence in all forms, aggregate, and use datasets for novel synthesis).  In handling these papers, similar to all reviews really, we will strive for rapid turnaround, and if sent out for review, we will also work hard to ensure that referees expert in synthesis can provide you with input.

The editorial associated with this section is now OA and online.
Let’s work together to find that big picture.

 

 

 

 

 

Can invasive species actually alter their environment so that more nutrients are available for them? Find out in the Early View paper “Non-additive effects of invasive tree litter shift seasonal N release: a potential invasion feedback” by Michael J. Schuster and Jeffrey S. Dukes. Below is their summary of the study:

Many woody invasive species change their environment to better fit their needs for resources, particularly soil nutrients like nitrogen. One way that they can do this is by accelerating the decomposition of leaf litter—an important step in recycling leaf nitrogen into a form that can be used by plants. However, much of what we know about the decomposition of invasive species’ litters, and their impacts on soil fertility, is based on observations of litter from an individual species decomposing by itself. This is problematic because litters rarely decompose by themselves in nature. More commonly, litters of multiple species are mixed together and decompose more quickly or more slowly than we would expect based on the decomposition rates of each species separately. Thus, we designed a litter bag experiment to examine how the litter of four invasive tree species decomposed differently when mixed with that of four native species, and how this difference might change as the invader became more dominant in the litter layer.

One year and 448 litter bags later, we found some surprising results. Indeed, native-invasive litter mixtures commonly decomposed at different rates than would have been predicted, but whether mixtures lost mass faster or slower than the predicted rate did not follow a strong, consistent pattern. In contrast, the release of nitrogen from these mixtures followed a very clear pattern of being slowed early on, but catching up to or exceeding the amount of nitrogen that would have been predicted at the end of the experiment. Implicitly, native-invasive mixtures were consolidating the release of their nitrogen until later on in the decomposition process, a time that corresponded to the period during which plants, especially the fast-growing invasive species, require the most nitrogen. This pattern was stronger in mixtures comprised mostly of the invasive species and for invaders that produced more nitrogen-rich litter. These findings, in concert with others’ on invasive species and nutrient cycling, led us to suggest that these invasive species might be shifting the release of nitrogen from the litter layer to a time when they are better able to use that nitrogen, and that this might be an important contributing factor to the success of some invasive species.

How are native and non-native-plants affected by various disturbances? Find out in the Oikos Early View paper “Non-native plant species benefit from disturbance: a meta-analysis” by Miia Jauni and colleagues. Below is the author’s summary of the study:

Disturbances, such as fire and grazing, are often claimed to facilitate plant species richness and plant invasions in particular, although empirical evidence is contradictory. Mixed results on the link between disturbance and plant invasions may be partly explained by differences in environmental and methodological factors among studies. To synthesize the literature on how plant species, both natives and non-natives, are affected by disturbances, we conducted a meta-analysis. More specifically, we examined how habitat and disturbance types, and methodological factors (study approach, the spatial and temporal scale of the study) modify the disturbance-diversity and disturbance-abundance relationships. We show that disturbance indeed facilitates the diversity and abundance of non-native plant species in communities where they are already present, while native plant species are less affected. However, the strength of the facilitative impact on non-natives depends primarily on disturbance type and on the measure used (species diversity or abundance), with grazing and anthropogenic disturbances leading to higher diversity and abundance of non-native plant species than other disturbance types examined.

 

Non-native plant species may be able to colonise disturbed patches more efficiently than native species.

How much of nutrients found in a lake actually originate from that lake? And from the surrounding grounds? From the ocean? In the new Oikos paper “Broad sampling and diverse biomarkers allow characterization of nearshore particulate organic matter” Alexander T. Lowe and colleagues study the flux of food across ecosystems. Below is their own summary of the paper:

The flux of food across ecosystem boundaries has important consequences for biological community and ecosystem dynamics. Nutrient poor environments are often subsidized by more productive adjacent habitats. For example, a kelp forest can support animals living in a deep submarine canyon through the transport of dead kelp. In marine and aquatic ecosystems, detritus, or decaying organic matter, produced through photosynthesis is thought to break down and mix into the water. This particulate organic matter (POM) can then be transported long distances by water motion, potentially feeding organisms living far away from the original location of photosynthesis.

 

Researchers from the Friday Harbor Laboratories collect ‘raw’ POM samples. The complex mixture in these jars was dissected using counts and diverse biomarkers. Photo: A. Lowe.

 

The origin of this organic matter is impossible to visually identify once the source has broken down into microscopic detritus. In coastal oceans this food source could come from land or sea. It is therefore common to use biomarkers like stable isotopes or fatty acids to track organic matter through food webs. This type of food source tracking depends on the assumption that each source has a unique biomarker signature that does not overlap the signatures of other potential sources. Using this ‘unique signature’ approach, studies have found high utilization of terrestrial plant detritus in freshwater lakes and coastal marine ecosystems. Similarly, kelp particulate organic matter has been traced into suspension feeders in an array of marine ecosystems. We were interested in the availability of different food sources to organisms feeding on POM. Most studies focus on the consumers, reconstructing the assimilated food sources using mixing models and the unique signatures. This method is often criticized because it does not account for natural variability in the source signatures, which is rarely measured directly. So we took a different approach. We looked directly at the POM to address this question; being a group of ecologists faced with a problem, we tried to count our way out.

 

An example of the complex composition of suspended particulate organic matter. Photo: A. Lowe.

 

Instead of assuming fixed signatures for each source, we made detailed observations of the living and detrital components of the POM and compared them to the stable isotope and fatty acid signatures of same sample. We took advantage of the natural variability of the coastal, temperate environment of the San Juan Islands, Washington, USA to look at food sources available. We expected the distinct seasons to be characterized by variable mixes of riverine, marine benthic and pelagic, and terrestrial sources of productivity. This broad sampling design allowed us to look at the relationships among the abundance of each POM component and the stable isotopes and fatty acid signatures under a range of natural conditions.

 

Nearshore suspended detritus in various stages of decay at Eagle Cove, San Juan Island. Photo: A. Galloway 2012.

 

What we found was 1) a lot of unidentifiable detritus and 2) an incredibly strong correlation among both biomarker methods and the phytoplankton component of the POM. Detrital particles numerically dominated every sample, which meant standard cell counts (especially those that ignore detritus) were potentially missing a big part of the story. So we adapted a point count method to estimate proportions of each category of POM (but did cell counts anyway). Phytoplankton abundance alone explained a lot of the variation in stable isotopes and fatty acids. Incorporating changes in the phytoplankton community explained even more of the variation in biomarker signatures. This signature overwhelmed the non-phytoplankton detritus, implicating phytoplankton as not only a major source of ecologically important fatty acids, but also as a major driver of the variation we see in biomarker signatures. Taking this result a step further we were able to establish the relationship between the proportion of each POM component and the biomarkers often reported to ‘identify’ them. Information that is critical for selecting and interpreting biomarkers. This simple method provided more information about source contribution than the ‘unique signature’ method and allowed us to pick apart the ever-present detritus. We advocate this method as a way to improve the use of biomarkers in complex ecological studies and to start making cross-system comparisons in order to better understand food sources available to POM consumers.

 

Suspension-feeding POM consumers (dominated by Balanus here) in shallow subtidal habitats of western San Juan Island. Photo: A. Galloway 2012.

If you haven’t yet heard the story of the body-snatching parasite lurking among wildflower populations across the globe, you certainly would not be alone. There is no need for alarm – it is a natural part of its ecosystem, and has likely followed its current hosts’ evolutionary paths for millennia. As such, it offers the opportunity to understand ecological, evolutionary, and environmental effects on infectious disease in wild populations, such as those responsible for many emergent infections threatening agriculture, wildlife, and human health. This is what the Early View Oikos paper “Elevational disease distribution in a natural plant-pathogen system: Insights from changes across host populations and climate”  by Abbate & Antonovics is about. Below, is the rest of the summary of the study:

 

Silene vulgaris plants infected with a pathogen that replaces pollen with dark fungal spores. The flowers’ dirty appearance earned the disease its name, “anther smut”.

 

Darwin and Linnaeus were among the first to notice the affected plants with their dirty appearance and altered genders. The tiny culprit, a complex of species-specific fungi in the genus Microbotryum, and its lovely array of flowering Pink Family hosts, has since risen to prominence as a model system for studying everything from genome evolution to how parasites compete for hosts. The fungus works its way through the whole plant and into the flowers, where it takes over the structures that would normally produce pollen (or induces their formation in plants that were otherwise female!) – forcing the plant to produce fungal spores instead. Insect pollinators visit these flowers, whose attractive petals and sugary rewards often appear completely normal, and are tricked into carrying those spores to the next host. As this pollination process is how plants mate, the fungus is essentially a sexually-transmitted infection, behaving epidemiologically similar to diseases of humans or animals driven by either sexual or vector-mediated contact. An infected plant is not killed but sterilized, and has little choice but to keep flowering, year after year, propagating the insidious disease.

 

A bee visits a diseased flower, which is likely still producing nectar. Fungal spores will travel on the bee to the next flower, hopefully (for the parasite) a new host to colonize.

For one particularly widespread host, the bladder campion Silene vulgaris, endemic disease had only rarely been found outside of high-elevation European alpine habitats, despite its weedy presence across the continent. Many diseases are limited to particular habitats within the larger range of their hosts. The most obvious and arguably important example is malaria, which is devastating in the tropics but largely absent from latitudes closer to the poles. Many studies have predicted that as the global climate warms, malaria risk will increase in more densely populated temperate zones, largely in response to shifts in vector distribution. However, others have questioned whether rapid aridification may also reduce risk in currently affected areas with less public health infrastructure. As understanding disease emergence hinges on un-answered academic questions about what factors drive the distribution of disease, we set out to test whether the presence of our little anther-snatcher in Silene vulgaris was similarly limited by environmental factors. It was equally possible that the host populations were simply not as abundant or connected at lower elevations, or that not enough botanists noticed or reported the disease while cataloging plant occurrence.

 

A bee visits a diseased flower, which is likely still producing nectar. Fungal spores will travel on the bee to the next flower, hopefully (for the parasite) a new host to colonize.

To do this, we went to the eastern French Alps, recording host population locations, size, density, and of course, disease. Back in the lab, we were able to use the GPS point of each population to get their proximity to one-another, as well as summaries of climatic conditions. What we found was that indeed, despite being common at high elevations, the disease was exceptionally rare in populations below 1300 meters in elevation. Furthermore, the cool temperatures, high precipitation, and more stable climatic conditions of diseased locations explained this distribution even after correcting for the fact that disease was most common in larger populations, which were relatively more frequent at higher elevations. This study sets up the opportunity to investigate environmental, evolutionary potential, vector distributions, and host resistance effects on the distribution of infectious disease in a natural model species that poses little risk to human health, wildlife, or agriculture. Such studies will be crucial to understanding, and ultimately anticipating, how climatic perturbations may impact disease dynamics and emergence.

 

Janis Antonovics (study author), enjoying an afternoon refreshment along the sampling route in the small alpine village of Les Terrasses, France. Citizens, farmers, and even sheep herders in the local community were always interested in why we were there, and often offered more than just water and lettuce from their gardens – they are a wealth of knowledge on the history, land use, and even biology of their local flora and fauna.

 

A bee visiting diseased Silene vulgaris, complete with visible dark fungal spores at the tips of protruding anthers.

Infected Silene vulgaris at the Col du Galibier, France.

The view of our study area from La Meije glacier near La Grave, France. Pictured: Jessie Abbate (L), lead author; Kerri Coon (R), field assistant and undergraduate researcher.

Shorter (ie, Twitter) version:

Fungal anther-smut disease in Silene vulgaris is restricted to host populations in high-elevation alpine climates.

 

Related website: Field assistant and undergraduate researcher Kerri Coon’s tumbler blog, documenting the 56 days she spent with me in the field tracking some of these populations. 56 reasons to be a biologist: http://kerri-lynn.tumblr.com/

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

How do seabirds use tunas to find more fish? Find out in the Early View paper “Facilitative interactions among the pelagic community of temperate migratory terns, tunas and dolphins” by Holly F Goyert and co-workers. Below is their short summary of the study:

In the Northwest Atlantic Ocean, researchers and fishers have been known to follow flocks of seabirds, particularly terns, in search of Atlantic bluefin tuna, Thunnus thynnus. We wanted to understand whether such “local knowledge” of tern-tuna associations, which has been described but not tested in the literature, is based on quantifiable community interactions. Marine biologists have speculated that these top predators have a commensal (i.e. mutualistic) relationship, such that terns benefit from feeding tunas, which draw attention to “bait balls”, then drive fish to the surface. We found positive, fine-scale, spatial and foraging (e.g. feeding) associations among tunas and terns (common, Sterna hirundo and roseate, S. dougallii), which supports our hypothesis that facilitation drives their ecological and behavioral interactions at sea, where tunas increase prey detectability and accessibility to terns.

 

common terns (Sterna hirundo) observed during a pelagic survey, 27 Sep 2006 (Photo:Marie-Caroline Martin).

The first author, Holly Goyert, observing for seabirds, marine mammals, and tunas during a pelagic survey

That predators affect prey populations and vice versa is well known. But how does the prey’s behavioral responses to predators affect populations of the prey’s prey? This was studied by Bradley Carlson and Tracy Langkilde in the Early View paper “Predation risk in tadpole populations shapes behavioural responses of prey but not strength of trait-mediated indirect interactions”. Below is Bradley’s summary of the study and some photos from the experiment:

It is old news that different populations of the same organism often differ from one another in a number of characteristics. Populations may vary in color, size, morphology, behavior – just about anything. A common cause of such diversity is that populations face different environments that favor different traits. In particular, local predator communities (that is, how many predators there are and what species of predators) can be highly variable and can affect prey behavior. Where predators are abundant and dangerous, prey ought to behave cautiously by hiding, fleeing readily, or being inactive and secretive. When the risk of predation is low, prey ought to pursue opportunities to eat and reproduce.

My doctoral advisor, Tracy Langkilde, and I tested whether populations of wood frog tadpoles (Lithobates sylvaticus) from ponds with high predation pressure showed stronger behavioral responses to predators than tadpoles from ponds with low risk of predation. When they smell a predator in the water, wood frog tadpoles (like many tadpoles) typically become inactive, swimming less and hiding more. We think they’d rather be active so they can consume lots of food, grow large and fast, and turn into frogs before their pond dries. But, if there’s a predator around, it’s more important to not get eaten.

 

Wood frog tadpoles swim in a pond mesocosm.

 

                We selected 18 ponds with wood frogs across Pennsylvania, representing a range of predator communities. Early in the year, I collected freshly-laid wood frog eggs to bring back to the laboratory so I could measure the behavior of the tadpoles. Later in the year (when tadpoles were swimming in the ponds), I used a net to collect random samples of animals from each pond. I’d then sort through the contents of the net to count the number of each kind of predator I found. These included dragonfly nymphs, newts, and other salamanders and insects. These data were used to assign each pond a value for how high the predation risk was; the more predators, and the more ‘dangerous’ these predators, the higher this number would be.

Brad Carlson uses a dipnet to sample a pond community.

                But what about those eggs I brought back to the laboratory? We hatched them into tadpoles at a research farm at Penn State University and, when the tadpoles were old enough, introduced them to pond mesocosms. Pond mesocosms are artificial ponds, smaller than most natural ponds but big enough to be reasonably realistic environments. Our mesocosms were created by filling large cattle-watering tanks with water and adding standard amounts of dead leaf litter. We also added a small amount of pond water, introducing bacteria, algae, and other microorganisms which flourish and create functioning ecosystems. Each pond that we collected eggs from was represented by two of the mesocosms. One mesocosm had a cage floating in it, which contained a dragonfly nymph (Anax junius), voracious and hardy tadpole predators. Regularly feeding the dragonflies extra tadpoles in these cages ensured that the mesocosm water smelled of danger but that the experimental tadpoles wouldn’t actually be eaten. The other mesocosm served as a control (with an empty cage), allowing us to measure the normal, ‘baseline’ activity levels of these tadpoles. After a few weeks, I measured how active the tadpoles were by quietly walking around the mesocosms and counting how many tadpoles I could see (their ‘visibility’) and how many of those visible tadpoles were moving rather than still (their ‘movement rate’).

Brad Carlson observes tadpole behavior in mesocosms.

Our analysis revealed that tadpoles from ponds with higher predation risk responded more strongly to predators than tadpoles from other ponds, spending less time visible, and slightly tending to move less. A good explanation for this pattern is that tadpole behavior is adapted to local environments, with generations of selection in high predation environments ensuring strong responses to predators. This is interesting in its own right though not too surprising. What we really wanted to know was whether this kind of variation in tadpole behavior affects the pond ecosystem. In particular, antipredator behavior often leads to trait-mediated indirect interactions (TMII). In this case, the TMII is an effect of the presence of a predator (dragonfly) on the tadpole’s own food (periphyton, a film of algae and other microbes and detritus growing on submerged surfaces). Dragonflies shouldn’t directly interact much with periphyton, but they should indirectly via their effect on a trait of the tadpoles – foraging activity. If dragonflies cause tadpoles to be less active and thus eat less food, then their food (the periphyton) should increase in abundance. We expected, therefore, that populations of tadpoles that respond strongly to predators should produce larger increases in periphyton than less responsive tadpoles.

Pieces of filter paper with collected samples of dried periphyton (green and brown matter) from tadpole mesocosms.

 

To test this we simply measured the mass of periphyton in the mesocosms by removing tiles we placed in their, scraping off the periphyton, and weighing it after drying. We found that, as expected, mesocosms with caged predators had much higher biomass of periphyton. However, the amount that periphyton increased when adding predators didn’t depend on how strongly the tadpoles responded to predators, nor did it depend on the predation risk in the pond from which the tadpoles came. In fact, tadpole behavior overall was a generally poor predictor of the amount of periphyton in the mesocosms.

This was unexpected, as we established a clear mechanism by which periphyton increases with predators (dragonflies decrease tadpole activity, decreased tadpole activity increases periphyton). Apparently, the amount the tadpoles actually eat is not perfectly linked to their activity: some tadpoles may become very inactive when predators are introduced, but still consume as much food as tadpoles that barely respond to predators. Do they switch their diets, or eat while hiding in refuges, or do most of their foraging at night? And, are tadpoles from ponds with more predators better at compensating for lower activity levels? These questions and more still remain, and will help us as we continue to try to understand how variation in behavior can impact ecosystems.

How carbon moves from terrestrial food-webs to aquatic ones are studied in the new Early View paper “Boomerang ecosystem fluxes: organic carbon inputs from land to lakes are returned to terrestrial food webs via aquatic insects” by K. Scharnweber and co-workers. Below is their summary of the study:

The TERRALAC-project (http://terralac.igb-berlin.de/) ran from 2010 to 2013 and was an interdisciplinary project, based at the Leibniz-Institute of Freshwater Ecology and Inland Fisheries, Berlin, Germany in collaboration with University of Potsdam and Technical University Berlin. Five PhD students worked in five subprojects. The overall aim of TERRALAC was to study the effects of terrestrial particulate organic carbon (tPOC) on shallow lake ecosystems. We wanted to find out, how terrestrial leaves that enter lakes in autumn are actually processed with the lake food webs and we wanted to test this on the natural spatial scale.

One prominent obstacle in studies on the effects and contribution of this allochthonous carbon on lake food webs is the problem of overlapping isotope values of the potential resources. Isotope signatures of the terrestrial carbon are often very similar to those of aquatic primary producers. TERRALAC chose a novel approach by using a tPOC tracer that is isotopically distinct, but also similar to the size and structure of natural leaves: maize (Zea mays) leaves.

Photo 1: Maize added into the littoral zone. The rope prevents it from floating into the open water.

In October 2010, we divided two small and shallow lakes, located in the rural area of Northern Germany approximately 100 km north of Berlin, in two equal halves. Both lakes are eutrophic and of similar size and depth. However, they have different alternative stable states: Gollinsee has turbid water and is dominated by phytoplankton, whereas Schulzensee has clear water and is dominated by macrophytes. We used plastic curtains to divide the lakes (Photo 1) from surface to bottom. With the help of many hands, we added the maize leaves into the littoral zone of the treatment sides of the lakes (Photo 2,3). By this approach we tried to mimic the natural input of tPOC by leaves in autumn.

Photo 2: Maize addition by hand in Schulzensee (October 2010).

Photo 3: Installation of the plastic curtain in Gollinsee.

Photo 4: Emergence trap used in our study.

In our article we present the flow of terrestrial carbon to lakes and back to its terrestrial surroundings via emerging insects (Figure 1). We focused on Chironomidae that have an aquatic-terrestrial life cycle and collected them as larvae, but also as adults using emergence traps (Photo 4). After emergence, they are known to become prey for terrestrial predators, for example for spiders that live in the riparian reed belts. Carbon isotope values of Chironomidae and spiders were significantly elevated in the lake treatment sides as compared to reference sides. As further demonstrated by isotope mixing models, contribution of maize was higher in Schulzensee, the lake where macrophytes are present. We conclude that structural complexity provided by the macrophytes may trap the leaves and by that enhance the food availability for the larval Chironomidae. In summary, we present the tight linkage between aquatic and terrestrial habitats and the cycling of organic matter across boundaries and borders.

 

 

 

 

What is climate change doing to plant–pollinator interactions? In the last decade, ecologists have focused on the possibility that climate change will shift the seasonal timing (phenology) of plants relative to their pollinators, reducing temporal overlap between interdependent species. In the Early View paper “Plant–pollinator interactions and phenological change: what can we learn about climate impacts from experiments and observations?” in Oikos , I evaluate the evidence that plant–pollinator overlap is changing as a result of climate change, and that such changes affect population persistence. I also discuss the strengths and limitations of different types of evidence for climate-change impacts. In particular, I explore the challenge of interpreting “temporal transplant” experiments, which manipulate the phenology of a subset of plants or pollinators in isolation, creating subpopulations of mistimed individuals in a matrix of unaltered phenology.

Observational data have shown us that, for the most part, plant and pollinator phenologies are advancing in parallel in response to warmer temperatures. While there are cases of plants blooming before their pollinators are active and consequently setting few seeds, there is no conclusive evidence yet that climate change is causing this “mismatch” to happen more often. There’s even less indication that pollinators are suffering from mismatch with plants—but pollinator fitness has received much less study. I suggest that there is much still to be learned about the direct effects of climate change (e.g., snowpack reductions, temperature extremes and fluctuations) on populations of pollinators and pollinator-dependent plants—effects that might be more demographically consequential than non-parallel shifts in phenology.

By Jessica K.R. Forrest

Photo of male Megachile on unopened flower head of Erigeron speciosus. © J. Forrest

Many animals are breeding earlier and earlier in response to a gradually changing climate – but what happens when a species encounters a dramatically different climatic regime such as a complete reversal of the summer-winter rainfall pattern? In our article,  “Phenological shifts assist colonisation of a novel environment in a range-expanding raptor”, we explore this question by investigating how variation in the timing of breeding and breeding success of black sparrowhawks Accipiter melanoleucus relates to weather patterns during their colonisation of the Cape Peninsula of South Africa.

Heavy rain can have pronounced effects on breeding success in raptors, flooding exposed nests and potentially impairing the ability of parents to hunt. In the eastern and north-eastern areas of South Africa the majority of rain falls in the summer months and black sparrowhawks breed during the dry and relatively cool winter. During the last half a century a number of bird species have gradually expanded their range south-westwards within South Africa bringing them into contact with a dramatically different weather pattern: in the south-western regions the rain falls mainly during winter, a complete reversal of what occurs elsewhere in their range.

In the 1990s, the first black sparrowhawks were recorded breeding on the Cape Peninsula, in the shadow of the iconic Table Mountain. Rising to over a 1000m, this huge lump of sandstone generates exceptionally high levels of rainfall in the immediate lee of the prevailing winds, during the winter months as deep depressions roll in off the Southern Atlantic Ocean.

In 2001 a long-term study of the black sparrowhawk population[http://blackspar1.wordpress.com] on the Cape Peninsula was initiated. In the first year fewer than a dozen nests were monitored but as the population expanded so did the project. A team of dedicated volunteers now follows the breeding success of over 50 nests each year. This hard work has generated a fantastic data set with which to explore how the unusual weather of the Cape Peninsula affects breeding phenology and the role that shifts in breeding phenology has played in the growth of this population.

We found that black sparrowhawks on the Cape Peninsula commence breeding up to three months earlier than eastern and north-eastern populations, and that breeding was suppressed during the months of heaviest rainfall. Earlier breeding attempts also produced more chicks. As a result of the shift in timing of breeding, the probability of population extinction was reduced by 23%, suggesting that this phenological shift could have assisted the colonisation of the Cape Peninsula. However contrary to expectations we found no strong evidence that black sparrowhawks were responding to local variation in rainfall within the Peninsula study area. We suggest that shifts in breeding phenology may be driven in part by other novel processes encountered during colonisation, such as interspecific competition for nest sites and lower temperatures during late summer than is the case in the rest of their range.

Clearly there is more to learn about how black sparrowhawks cope with the differing environments they encounter as they have spread westwards. Looking forward, PhD student Gareth Tate is using nest cameras and satellite tracking technology to investigate in further detail how weather influences hunting behavior.

The Authors through Arjun Amar

 

Papers published in Oikos should meet the principal criteria to generate synthesis in ecology. Synthesis can be created in different ways and definitively obtained when long-term data sets, novel analytical tools and good hypotheses are merged. The first editor’s choice for the June issue is the paper by Karen Lone and colleagues on multi-predator landscapes of fear. Motivated by challenges to manage large carnivores in Scandinavia in relation to human conflict, the authors used an extensive dataset containing Lidar data, behavioural data and hunting information to demonstrate the interactive impact of multiple predators on predation risk of a single prey species. By means of this integrative approach, the authors demonstrate a predation risk from humans and lynx on roe deer in areas with a high vegetation cover, but an additive impact in more rocky locations. As such, the study demonstrates the complexity of predator-prey interactions in real landscapes, and clearly emphasises the need and value of individual-based ecology to understand interactions in (simplified) foodwebs.

Oikos has decided to highlight meta-analysis papers because of their principal role to create synthesis in ecology.  Chris Lortie will be Editor-in-Chief for this category of papers (look out for his editorial in the August issue). Meta-analysis papers will be published OA for three months after publication. Ward and colleagues tested the performance of time-series forecasting models for natural animal populations based on more than 200 datasets of vertebrate surveys. Such a meta-analysis is considered essential because of the increasing demand to forecast population dynamics under different global change scenarios. While forecasting approaches using non-mechanistic statistical models have greatly evolved the last decades in population biology, still a limited amount of such models are commonly used. By performing a statistical competition experiment, the authors tested the predictive performance of 49 different forecasting models and found simple models to behave well after all, although increasing model complexity fitted time series better in case of species with cyclic population dynamics.

Editor’s choice papers are free online for three months!

The ants underfoot forage faster as the ground warms each day. Likewise, the fish in nearby streams and the worms and other organisms that parasitize these fish speed their activities as the water warms. Above the stream, dragonflies engage in more aerial battles each hour for prime perches as the air warms. We have all witnessed these quickenings, as insects and other ectotherms, organisms whose body temperature are primarily environmentally determined, become more active and interact more quickly in hotter environments. How much faster do such biotic interactions increase with temperature, and why?  This is studied in the Early View paper “Rates of biotic interactions scale predictably with temperature despite variation” by Bill Burnside and co-workers. Their sumary of the study continues here:

Anderson Mancini, Creative Commons – Flickr

 

In this meta-analysis, we look across taxa and habitats to assess the temperature dependence of biotic interaction rates, such as herbivory and competition, between two species. We hypothesize that these rates will increase approximately exponentially with temperature, mirroring the temperature dependence of respiratory metabolism generally. This hypothesis is inspired by the metabolic theory of ecology, which suggests that many ecological patterns and processes are functions of individual metabolic rates of the organisms involved. These rates vary characteristically with body temperature, which affects the rates of cellular chemical reactions. Biotic interactions are metabolic because they involve exchanges of energy and materials between organisms and their environment and because they are inspired by basic metabolic demands, like the need to eat.

Matthew Britton, Creative Commons – Flickr

 

This work was intriguing because even though we were not interacting ourselves with all the amazing organisms in our analysis, like those pictured here, we did not know what we would find. The studies were often focused on a related question and just happened to include temperature as a variable or did not include graphs, so it was tough to visualize how some rates varied with temperature. And the rate terms varied by their nature, from the rate ground beetles catch and eat fruit flies to the rate sea lice parasitize fish.

Watershed_Watch, Creative Commons – Flickr

 

Seeing the results for the first time—the generally parallel lines, each with a slope indicating how interaction rate scales with temperature—was amazing. Our results generally supported our hypothesis, but there was also a great deal of variation. We could only find a fairly small sample of studies on most interaction types, which probably accounts for some of this variation, but organisms vary in their level of thermal performance and peak response, among other traits, which surely accounts for variation when different species interact.

Understanding how temperature affects biotic interaction rates is more important than ever in our warming world. The answers won’t be entirely straightforward and may vary among places, species, and communities, but this study offers basic insight to inform our search. 

Vernal pool ecosystems emerge from winter and spring rains that fill shallow depressions in the earth, resulting in small patches of wetlands spread throughout the Central Valley of California, USA. These pools act as a crucial habitat for a diverse community of annual plants, many of which are endemic to the region. Many of these species complete the majority of their entire lifecycle within the short duration that the pool exists. As the standing water evaporates, a stunning array of wildflowers is produced from the plant species that co-occur in these temporary ecosystems. The endemic diversity of these pools, coupled with the short lifespan and small size of the species, makes them an ideal model system for testing questions of community assembly. In the study “Functional trait differences and the outcome of community assembly: an experimental test with vernal pool annual plants” in Oikos, Nathan Kraft, Greg Crutsinger, Elisabeth Forrestel and Nancy Emery measured functional trait differences between species in the pools and tested whether these characteristics could be used to predict the outcome of interactions among plant species and, ultimately, the processes structuring the vernal pool communities.

Kraft and colleagues used a greenhouse experiment with eight different annual vernal plant species and grew them together in all pairwise combinations, so that every species had a chance to interact with every other species. They also submerged these combinations in tubs of water for different amounts of time to mimic growing at different depths in a vernal pool. Prior work in this system has found that the recession of water in the spring generates a gradient of species composition along the sides of vernal pools. The authors observed that plant species tended to do better when they had larger leave size, lower specific leaf area (fresh leaf area divided by dry leaf mass), and greater investment in lateral canopy spread than their neighbors. It also turns out that not all individuals within species are equal in these interactions. The authors took an additional step relative to many trait-based studies and measured functional traits for all individuals in the experiment. Models that incorporated individual trait differences did a better job of predicting the outcome of the interactions than models using only species average trait values.

The results of this study suggest that plant traits can be used to help understand the outcome of interspecific interactions in vernal plant communities. It’s also clear that individual trait differences matter. If resources allow, researchers can boost their predictive power by considering trait differences among individuals, instead of focusing on the average traits for different species, which has been the standard practice. There is still more work to be done to understand how vernal pool communities are assembled, as the patterns Kraft and colleagues observed in greenhouse did not strongly match patterns seen in natural pools, suggesting other undiscovered factors are also contributing to species distributions. Ongoing work from Nancy Emery and others will continue to shed light on the processes structuring these fantastic communities in the near future!

How do plants react to seasonal extremes? Find out more in the new Early View paper “Leaf and stem physiological responses to summer and winter extremes of woody species across temperate ecosystems” by Elena Granda and co-workers. Read Elena’s summary of the study here:

Our paper presents evidence that winter stress in the temperate region is more extreme than summer for forests that do not experience summer droughts, but also for those where summer drought combines with winter freezing. In this study we compiled existing literature to identify overall trends of the impact of seasonal extremes on plant performance (leaf and stem physiological responses). We further compared the general patterns over the temperate region with a continental Mediterranean case study subject to intense summer droughts and winter freezing.

Continental Mediterranean and riparian forests at Alto Tajo Natural Park (Spain) during a) summer drought and b) winter freezing

 Although it is known that winter cold limits plant performance, as is also the case for summer drought in dryland ecosystems, our study revealed that across temperate forests: (i) winter is commonly an equal or even stronger stress than summer, including particular cases of Mediterranean vegetation; (ii) many species are able to maintain stomata open during winter, favoring carbon gain over most of the year; (iii) stomatal conductance and xylem hydraulics show a coordinated seasonal response at sites without summer droughts, and (iv) deciduous angiosperms are the most sensitive to climatic stress.

These results suggest that the differences among functional types in seasonal dynamics of physiological performance are strong enough to advocate their importance in determining ecosystem productivity throughout the year, especially in ecosystems where carbon gain is limited to a few months. These patterns present a baseline against which to compare shifts for key plant species and communities with ongoing climate change.

Bird pollination in Europe? Really? Well, find out in the Early View paper “Flower visitation by birds in Europe” by Luis P da Silva and co-workers. Below is Luis summary of the paper:

Birds are among the most studied animal groups and are most likely the one that attracts more general public attention. These winged animals, are known throughout the world for their interactions and coevolution with plants. They are known to be very important for several plant groups, providing seed dispersal and promoting sexual reproduction through pollination.

When anyone hears about birds pollinating plants, their first thoughts go to hummingbirds, which are very specialized bird pollinators that are able to hover. However, there are other bird groups that are not considered so specialized in pollination (and unable to hover), but well known to pollinate plants, as the honeyeaters. This bird group, somewhat specialized in taking nectar and consequentially pollinate flowers, are present in almost all over the world, except in Antarctica and Europe. If in Antarctica that is not unexpected, in Europe (and actually in almost all the Western Palearctic) that seems a little odd, that how such ubiquitous and abundant food source is not recognized to be regularly exploited by any bird species. With this, insects are often considered the only ecologically relevant pollinators in Europe. Nevertheless, generalist birds are also known to visit flowers and in some cases to successfully pollinate plant species around the world.

In Europe there are several scattered publish records of flower visitation by birds. We carried out a fine literature search and compiled our own observations to estimate the extent, richness and ecological relevance of this mutualistic interaction. These interactions were not only of direct feeding observation, but also from pollen found attached to feathers, in faeces and stomach contents. We found that 46 bird species visited flowers of at least 95 plant species, 26 of these being exotic to Europe, yielding almost 250 specific interactions inside Europe. Additionally, we registered four more European bird species interacting with 12 different plant species outside Europe. Despite these numbers, only six plants species, both native and exotic, were confirmed to be efficiently pollinated by birds in Europe. We argue that the ecological importance of bird-flower visitation in Europe is still largely unknown, particularly in terms of plant reproductive output. We suggest that nectar and likely pollen are important food resources for several bird species, mainly during winter and spring, especially for tits (mainly Cyanistes), Sylvia and Phylloscopus warblers. The prevalence of bird flower-visitation, and thus potential bird pollination, is slightly more common in the Mediterranean basin, which is a stopover for many migrant bird species, which might actually increase their rule as potential pollinators by promoting long-distance pollen flow. We argue that research on bird pollination in Europe deserves further attention to explore its ecological and evolutionary relevance.

Different factors that effect predation in marine habitats are explored in the Early View paper “Differences in predator composition alter the direction of structure-mediated predation risk in macrophyte communities“ by Simone Farina and co-worker’s. Below is Simone’s short summary of the study as well as a reflection on the history that lead to the study.

Using sea urchins as model prey we examined the role of structural complexity in mediating predator-prey interactions across three bioregions: Western Mediterranean Sea, Eastern Indian Oceanand Northern Gulf of Mexico. As expected biomass of the habitat structure and fish predator abundance were the main determinants of predation intensity. Interestingly though, the direction of structure-mediated effects on predation risk was markedly different between habitats and bioregions. In Spain and Florida, where predation by fish was high, structure served as critical prey refuge, particularly for juvenile sea urchins. In contrast in Western Australia predation was generally higher inside the structure where bottom predators were more abundant.

Gallery 1: Meditarrenean Sea

In this sense, as a Mediterranean student I will never forget the days of field work in WA. We had to look for Heliocidaris erythrogramma, the Australian model prey, the equivalent of Paracentrotus lividus in the Mediterranean Sea, and it was like looking for sparrows in the Amazon rainforest. Kelp was full of huge gastropods. Every time I moved a few shoots I had the impression of seeing any kind of tail run away quickly. It was very easy to get distracted from my search. One time we found a huge Coscinasterias calamaria (sea star) remained attached to a fishing line used to mark one of the sea urchins after having swallowed it entire. In seagrass ecosystems (Amphibolis griffithii and Posidonia sinuosa) we observed many little and coloured sea stars (Patiriella brevispina) approaching day by day to our sea urchins and finish them one after the other. In Australian seagrass ecosystems, working to head down supposed some time to have a look around to check for unexpected arrivals of huge sting ray, as ufos flying over a landscape. Macrophyte communities that we explored in Australia are totally different from the Mediterranean ones, so it does not surprise me that structures works in different ways. It was a really pleasure to carry out this experience and I think I’ll have a good story to tell my grandchildren.

Gallery 2: Australia

By comparing fish communities with bird communities Kirsten Nash an co-workers assess the appropriateness of different size distribution indices used in a variety of studies. The analyses resulted in the Oikos Early View paper “Habitat structure and body size distributions: cross-ecosystem comparison for taxa with determinate and indeterminate growth”. Below is the author’s own summary of the paper:

How the study arose:

The study resulted from conversations at the working group ‘Understanding and managing for resilience in the face of global change’, hosted and funded by the USGS Powell Centre for Analysis and Synthesis in Fort Collins, Colorado (https://powellcenter.usgs.gov/). The working group came about through a chance meeting between myself and one of the other authors of our study (Shana Sundstrom) at the 2011 Resilience Conference in Arizona. We were both starting our PhDs addressing similar questions but in different ecosystems: Shana primarily focuses on birds, whereas my research looks at coral reef fish communities. Participants in the working group come from Canada, USA, Sweden, South Africa and Australia.

Photo of the ‘Managing for resilience’ working group at the USGS Powell Centre in Fort Collins, Colorado:

Description of our group’s focus and short summary of the paper:

An ecosystem can be in a number of different forms or states, such as a reef covered in many corals vs. a reef with large areas of thick algae and little coral. The ability of an ecosystem to remain within its initial form (e.g. coral reef) when impacted by disturbances resulting from rapid global change, rather than shift to another state (e.g. algae reef), is called the resilience of the ecosystem. Until recently, a lot of the work that has looked at the resilience of ecosystems has been theoretical. Our working group focuses on putting this theory into more practical terms, i.e. understanding how likely is it that the ecosystem will remain in its current form over time, as this directly affects natural resources on which we rely for food, water, etc.

 

An important step in this process was to take methods that had initially been developed to look at terrestrial taxa, and explore their appropriateness for marine systems, to ensure that our work was relevant across a range of ecosystems and wasn’t limited to terrestrial studies. The result was our study recently published in Oikos, where we compare the ability of different animal size measurements to highlight the effect of a variety of habitats on the bird and fish communities that live within them. We completed fieldwork on fish communities inhabiting reefs of the Great Barrier Reef and the Seychelles and used published data for bird communities in Borneo (Cleary et al., 2007, Ecological Applications) and the Lofty Ranges, Australia (courtesy of Hugh Possingham and the Nature Conservation Society of South Australia). The study shows that both average and individual size measurements are useful for showing the effect of habitat on bird communities. In contrast, for fishes, we need to incorporate the size measurements of all individuals within a community to show the effects of habitat on fishes.

 

 

An open future for ecological and evolutionary data?
Amye Kenall*, Simon Harold and Christopher Foote
doi:10.1186/1472-6785-14-10

A very succinct and accurate editorial on the future directions needed for data sharing in ecology & evolution was recently published at BMC Ecology. The key issues for ecology & evolution were identified and included the following:

Opportunity cost: available data reduces costs, provides opportunities, and serves local stakeholders

Shared benefits: new forms of collaboration, discovery, and accelerated synthesis will emerge

Blood, sweat and tears: long-term datasets are hard won and it is difficult to let them go (public)

A bigger picture: macroecology and other relatively new ways of doing ecology need open data

Data management: metadata is critical, always, and for ecology/evolution in particular because the ‘lab’ is often outdoors

Credit where credit is due: many new reputation economy tools and reward systems are in place to serve as incentives for all scholars not just for ecology and evolution

Transparency and trust: we review the manuscripts of others, why should datasets be free from scrutiny?

Each issue is well described. The one that clicked the most for me was the ‘blood, sweat, and tears’ argument as I have heard it made by many ecologists. Fieldwork can be grueling.  We also hope that we will reuse our own datasets many times. However, I suspect that we do not. Let them go free. As a personal goal, I have mentioned the idea of #ecodataweek on twitter as a good push to myself via a bit of friendly competition to get stuff out there more too.

Oikos also partners with Dryad, and I hope that this editorial likewise inspires you to publish your data.  I would also love to see a more in-depth set of analyses for Oikos readers on these topics and how they relate to the journal mission of ‘novel synthesis’ and synthesis science in general.

Additional resources to consider:
1. DataONE for data management planning tools and a list of best management practices for data documentation (pdf link is best).
2. A good read on how our discipline has likely crossed into the realm of big data.
3. The pivotal nature of data sharing to the future of publishing in ecology.
4. Re-read the file-drawer problem papers such as the Csada et al. 1996 Oikos paper on the topic (classic for ecology but still feels modern with issues of limited OA and accessible data).

 

 

 

“Nature is much more complicated” than predicted in theoretical  models. In the Early View Paper “Matrix models for quantifying competitive intransitivity from species abundance data”, Werner Ulrich and colleagues try to fill a gap between models and mother nature when it comes to competition interactions.

Below is their summary of the study:

Ecologists have devoted much effort to inferring competitive processes from observed patterns of species abundances, morphology, and particularly from changes in the spatio-temporal distribution, (i.e. species co-occurrences). Classic assembly rules models, derived from the principle of competitive exclusion, predict that differences in competitive abilities should cause non-random patterns of species occurrences among sites and generate inequalities in species abundances within sites. Competitively inferior species are predicted to occur less frequently and at lower abundance, and an important and largely unresolved question is how such species can persist in a community over long time periods (also known as Darwin’s paradox and nicely explained in http://www.wbez.org/blog/clever-apes/2011-11-22/clever-apes-22-paper-covers-rock-94295) .

Simple competition models assume that species can be ranked unequivocally (A>B>C…>Z) according to their competitive strength. However, nature is much more complicated and intransitive competitive networks can generate loops in the competitive hierarchy (e.g. the rock-scissors-paper game, in which A>B>C>A). Importantly, such loops allow weak competitors to coexist with strong ones. Additionally, the structure of such loops might be modulated by environmental factors. Experimentally competitive strength can be tested with simple two-species systems. Testing competitive interactions in many-species systems requires an increasing number of species exclusion experiments.

Up to now no comprehensive theoretical framework existed to infer competitive loops from observed patterns of species abundances. Existing mathematical models based on presences and absences of species (on perfect competitive exclusion) have rarely been applied to empirical data. Our new paper in Oikos seeks to fill this gap in our knowledge. We introduce a statistical framework for evaluating the contribution of intransitivity to community structure using species abundance matrices that are commonly generated from replicated sampling of species assemblages. We use a stochastic back-engineering procedure to find a transition probability matrix that predicts best observed distributions of abundances in an ordinary Markov chain approach. We then use a probabilistic argument to convert this transition matrix into a pairwise competition matrix that contains the information of competitive strength between all species in the community. Our approach can be used for abundance data, time series, and abundances in combination with environmental data. Our case study on necrophagous flies and their hymenopteran parasitoids revealed strong hints towards instable competitive hierarchies. In other words the competitive outcome in these communities (having at least five species) strongly depended on environmental conditions but also on the spatial structure of fly and parasitoid occurrence.

We hope that our new approach sparks a fresh new look at competitive interactions in ecological communities and helps to assess and appreciate the importance of intransitivity for the coexistence of species in natural communities. We fell the need for joint approaches that link existing methods using the temporal and spatial co-variation in species abundances and occurrences with methods (like our) that reconstruct competitive hierarchies. 

Bimodality – the characteristic of a continuous variable having two distinct modes – is of widespread interest in data analysis. This is because, in some cases, we can use the presence or absence of bimodality to infer something about the underlying processes generating the distribution of a variable that we are interested in studying. In ecology, tests of bimodality have been used in many different contexts, such as to understand body size distributions, functional traits, and transitions among different ecosystem states. But a lack of evidence for bimodality has been reported in many studies. Our paper “Masting, mixtures and modes: are two models better than one?”, now shows that a widely-used statistical test of bimodality can fail to reject the null hypothesis that focal probability distributions are unimodal. We instead promote the use of mixture models as a theory oriented framework for testing hypotheses of bimodality.

Our interest in this problem arose with the publication of Allen et al. 2012 Oikos 121: 367–376. The paper impressive synthesised 43 years of seeding patterns in a New Zealand mountain beech Nothofagus forest. Seed production in these trees is interesting because a population can go several years without reproducing and then all the individuals in a population will do so. Such intermittent and synchronous reproduction is also known as mast seeding.

 

Dense Nothofagus forests (dark green) dominate mountain-sides in Fiordland, New Zealand

 

In their paper, Allen et al. tried to infer the importance of resource limitation in driving mast seeding patterns by describing various characteristics of seed production. A key finding was that they could not reject the null hypothesis that the distribution of annual seed production was unimodal using an empirical calculation known as Hartigan’s dip test. Allen et al. 2012 concluded that few studies could ‘robustly test for bimodality’ because they lacked ‘long time-series’ and used questionable methods.

 

Nothofagus solandri var. cliffortioides trees in Fiordland, New Zealand

The bimodality result inspired a lot of reflection. We were interested in why we might consider an annual count that takes values larger than zero at more than 2 year intervals to ever even present two modes. Populations should only have one mode because the single most frequently observed seed count will be relatively low, on average, in most years. Thus, plants can never be bimodal when a single distribution is fit to seed counts – even if they alternate annually, on average, between the absence and presence of seed production. This is because of the underlying statistical nature of seed counts, which we describe in further detail in our paper.

Stepping back further from the problem, we began to realize that there is a need to consider multiple probability models, each with at least one unique mode, where plants flower at >2 year intervals.We illustrate these ideas by analysing 37 years of data from five grass species in New Zealand. Critically, we found clear evidence for bimodality using mixture models that associate distinct probability distributions with medium- and high- versus non- and low-flowering years. We expect these patterns to be driven by different processes and hence, modelled by different probability distributions. We found no evidence for bimodality with Hartigan’s dip test that assumes a single probability distribution can be fitted to all the data. Our findings show the importance of coupling theoretical expectations with the appropriate statistical tools when predicting the responses of ecological processes.

 

Snow tussock Chionochloa rigida flowering in Fiordland, New Zealand

The authors through Andrew J. Tanentzap

Talk about choosing between pest and cholera! A bird on migration, has a tough job, and with a virus infection in the body, the job is even worse! In the early View paper “A tradeoff between perceived predation risk and energy conservation revealed by an immune challenge experiment”, by Andreas Nord and co-workers.

Below is Andreas summary of the study:

Birds, like man, must maintain a high and even body temperature to function properly. This is a challenging task, not least in winter when the internal temperature may be some 50-60 °C above that of the surroundings. It is not surprising that this challenge requires high food intake. In fact, a blue tit, which is a common garden and forest bird across Europe, must sometimes put on 10 % of their body weight as fat on a daily basis during cold winter days. A human of average weight would have to eat some 200 hamburgers to ingest the same amount of fat.

As if this was not enough, the time of peak food demand often coincides with the time when food resources are the most difficult to obtain. To overcome such hardships, many animals actively reduce their body temperature at night (nocturnal hypothermia), a process that substantially lowers their energy demands. Yet the use of nocturnal hypothermia is often not enough to avoid the risk of starvation, because the demands from other body functions compete for the same fat reserves. In these situations, birds may have to prioritize surviving the night by reducing the use of other costly functions, such as the immune defense system. In other words, because food availability is limited in winter, it may not be possible to maintain sufficient amounts of body fat at the same time as an adequate defense against invading pathogens.

This was the subject for our study, in which we investigated how an activated immune defense system impacted on the use of nocturnal hypothermia and behavioral strategies for minimizing energy expenditure in wild blue tits in southern Sweden. Contrary to our expectations, an immune response did not cause birds to change their use of nocturnal hypothermia, which could indicate that any energy costs of the immune defense system are not large enough to interfere with energy conservation processes. However, birds with an ongoing immune response showed a different behavior compared to healthy birds, which was manifested as an increased use of sheltered roosting sites when the immune response was at its peak. Using such roosting sites often confers energy savings, because birds are less exposed to wind and temperatures are higher than those outside. However, sheltered roosts often come at the expense of increased predation risk, because these roosts may be easier to locate and escape prospects are typically relatively low upon detection.

We interpret this increased risk taking behavior in sick birds as consequences of a higher need to exploit the energetic benefits of sheltered roosts. Because this required birds to accept a higher predation risk at night, our results may indicate that energy stress from less efficient thermo-regulation poses a higher mortality risk for sick birds than does any predation risks pertaining to sheltered roosting sites. This was not the case for healthy birds, whose thermo-regulatory capacity was not impaired by an ongoing immune response. These birds instead actively avoided sheltered roosts, because their main source of overnight mortality might indeed have been the risk of predation.

Natal dispersal is a complex process but what could be the role of endo-intestinal parasites in dispersal propensity, distance and date of departure? In our article “Parasite abundance contributes to condition-dependent dispersal in a wild population of large herbivore” we look at this question on a roe deer population inhabiting a fragmented and anthropogenic landscape in South-West France.

Parasite abundance has been shown to have major consequences for host fitness components such as survival and reproduction. However, although natal dispersal is a key life history trait, whether an individual’s decision to disperse or not is influenced by the abundance of parasites it carries remains mostly unknown. Current and opposing hypotheses suggest that infected individuals should either be philopatric to avoid the energetic costs of dispersal (condition dependence) or disperse to escape from heavily parasitised habitats.

Our study site hilly and fragmented in the “coteaux de Gascogne” in South-West France.

 

Roe deer were capture during winter, we sample fresh faeces and we collared them with a GPS collared in order to follow their movement during approximately one year before to release them in site. Their natal dispersal behaviour could thus be evaluated with accuracy.

 

Collection of faeces sample during marking

 

Back to the field with a beautiful GPS collar

Our results show that dispersal propensity generally decreased with both increasing nematode abundance and with decreasing body mass. Within the dispersing segment of the population, individuals with high nematode abundance left their natal home range later in the season than less parasitised deer. These results clearly show that parasite abundance is an important component of condition-dependent dispersal in large herbivores. However, unexpectedly, three individuals that were both heavily parasitised and of low body mass dispersed. We suggest that this “leave it” response to high parasite levels in the natal habitat could represent a last ditch attempt to improve reproductive prospects, constituting a form of emergency life history strategy.

The authors through Lucie Debeffe who also took the photos

How life-history traits vary across longitude is studied in birds in the Amazonas in the Early View article “Variation in tropical bird survival across longitudes and guilds: a case study of the Amazone” by Jared D Wolfe and co-workers. Below is Jared’s summary of the paper:

Measuring the annual survival of birds, or the probability of a bird living from year-to-year, has fueled theory regarding life history strategy in temperate and tropical birds. For example, because tropical birds have fewer young over the course of a year relative to their northerly counterparts, scientists have often expected tropical birds to exhibit higher survival than temperate birds as part of a ‘trade-off’ in life-history strategy. In our paper we examined variation in annual survival among birds across the Amazon. We used a decade of bird capture data from the central Amazon to estimate the annual survival of 31 bird species and compared our results with those from western and eastern Amazonian forests.

We also examined differences in annual survival between bird species that differ in mass, foraging and nesting behavior at our study site in the central Amazon. In general, community-wide annual survival was remarkably similar across the Amazon, but several species did exhibit dramatic differences in survival estimates. The most striking variation in estimates of survival was exhibited by the White-plumed Antbird (Pithys albifrons), for which survival estimates were nearly twice as high in eastern than the western Amazon, but intermediate in the central Amazon. We also found that nest architecture moderately influenced annual survival of birds at our study site in the central Amazon. Our results suggest that geographic variation in survival may be significant for widespread Amazonian species.

How altered temperature might affect competition and herbivory in plant communities is studied in the early View paper “Concurrent biotic interactions influence plant performance at their altitudinal distribution margins” by Elina Kaarlejärvi and Johan Olsson. below is their summary of the paper:

The idea behind this paper was to test whether herbivory and competition influence growth and reproduction of lowland and tundra forbs at different altitudes. Previous studies had indicated that these biotic interactions could play a role in determining species altitudinal distributions, but this has been rarely experimentally tested.   We studied this in subarctic Abisko, in northern Sweden, on meadow habitats at two altitudes, at 600 and 900 m a.s.l. We selected five study sites at the two altitudes, each of them consisting of a pair of plots: one plot was fenced against large mammalian herbivores, while another was left open. Nested within this herbivore exclusion treatment we carried out biomass removal treatment to investigate effect of plant-plant interactions. We planted seedlings of lowland and tundra species to both altitudes and followed their growth and reproduction over two growing seasons.

Studying plant-plant interactions. Planting seedlings of lowland and tundra forbs to a subplot without neighboring vegetation at a low altitude site.

 

A fence against large mammalian herbivores in a study plot at a high altitude site. Early summer visit to the study sites to record signs of winter herbivory and check the condition of the fences.

We had expected to find competition at low altitudes and facilitation at high altitudes, but found that competition prevailed in both altitudes. However, high-altitude tundra forbs suffered more from competition; neighbor removal increased the proportion of flowering individuals and tended to increase growth of one of the high-altitude species more at low altitudes. Since the low altitude sites were about 2°C warmer (summer air temperatures) than high altitude sites, these results suggest that climate warming may strengthen competition and potentially shift lower distribution margins of high-altitude forbs upward. Interestingly, mammalian herbivores may counteract these climate-driven distribution shifts, as they reduced the growth of lowland forbs and enhanced the flowering of tundra forbs.

Lots of traits are climate dependent! In the Early View paper in Oikos “Genetically based latitudinal variation in Artemisia californica secondary chemistry” by Jessica Pratt and co-workers, terpenes are studied under different climatic situations.Below is a summary of the paper: 

Gradients in environmental conditions can serve as a ‘space for time’ substitution when trying to understand how species might respond to current and future environmental change and have thus become the focus of much recent work. Environmental gradients and gradients in biotic interactions often result in corresponding gradients in plant traits within a species. In our study, we examined variation in leaf terpene chemistry for the foundation species California Sagebrush (Artemisia californica) in Coastal Sage Scrub habitat across a 700 km latitudinal gradient in California. This gradient is characterized from south to north by a four-fold increase in precipitation.

Coastal Sage Scrub community in the Santa Monica Mountains with Californica Sagebrush in foreground

We collected California Sagebrush from five source populations distributed across this gradient and grew them in one common environment where we manipulated precipitation. Such common environment studies, when done in conjunction with environmental manipulations, provide a powerful approach to pinpoint the underlying causes of variation in plant traits and determine how such variation relates to large-scale ecological variation.

Coastal Sage Scrub community in the Santa Monica Mountains with Californica Sagebrush in foreground

Terpenes – one of the most diverse groups of plant secondary compounds – are important in providing defense against herbivores and also play several additional roles in the community. They are involved in plant-plant communication, drought and thermal tolerance, and adaptation to fire, and can influence plant relationships with other plants, animals, and microorganisms. We tested for genetically based variation in leaf terpene richness, diversity, concentration, and composition and examined whether precipitation was a key selective force on terpene chemistry.

California Sagebrush experimental garden plot

Our results showed that California Sagebrush source populations differed in terpene richness, diversity, concentration, and composition, with terpene composition and concentration varying clinally along the gradient. Plants from source populations that were closer together geographically had a more similar composition of terpenes than those farther apart, and terpene concentration decreased clinally from south to north. Our manipulation of precipitation suggests that selection for lower terpenes under increased precipitation may underlie this clinal pattern that we observed. Interestingly, we did not see a direct influence of the precipitation manipulation on terpene chemistry indicating these traits may not be phenotypically plastic in response to altered precipitation.

We conclude that changes in terpene chemistry under projected future climates will likely occur only through the relatively slow process of adaptation, and this will have important consequences for California Sagebrush’s interactions with the environment and a diverse community of associated species.

Have you ever tried to summarize your research in a poem? This haiku summarizes the Early View paper “Population-level consequences of risky dispersal”, by Allison K. Shaw and coworkers.

risky dispersal
whether too much, too little
both suboptimal

to selfishly leave
more or less than the others
may just hurt us all 

Oceans, they scare me
Nearby islands, too, stay far
I prefer it so.

Below, is a more traditional popular summary of the paper:

All living organisms move (disperse) at some point during their life. Many plants produce seeds that disperse away, and the offspring of most animals eventually grow up and move away from their parents. Moving has benefits as well as costs. By moving, an individual can find better food resources, or potential mates. However, by moving an individual also leaves behind familiar areas and faces the risk of possibly never finding a place to settle, or even dying along the way. So for each individual, there is some ‘best’ amount of movement: not too much and not too little.

However, moving individuals can also influence the population they live in: movement determines how spread out the population is across a habitat, and how much movement there is between different areas of the habitat. Therefore, from the perspective of the population, there is also a ‘best’ amount of dispersal. If individuals are spread out across the habitat, this can allow the population to reach a larger size, which increases the probability that the population will persist over time.

The question we ask in this paper is: what is the relationship between the amount of dispersal that is ‘best’ for an individual and the amount that is ‘best’ for the population? If they are not the same, which one is bigger and why?

To answer this question, we built a model (see Figure). We find that generally (1) when the area a population occupies is small, (2) where the habitat can only support a few individuals and (3) when there is a high risk of dying during dispersal, the amount of dispersal ‘best’ for an individual is smaller than the amount ‘best’ for the population. In these cases, the population size would increase if only individuals dispersed more. This suggests that as a conservation strategy for endangered species, restoring habitat may not be enough but may need to be combined with some form of assisted movement.

 

 

A schematic of our model. Individuals live in a habitat area of limited size, made up of smaller patches. If individuals disperse (leave the patch where they were born) they can either land successfully in another patch, die during dispersal, or die if they move beyond the habitat edge.

 

 

 

 

Apex predators are large carnivores that occupy the top trophic level of food webs. Globally, apex predators are assailed by disturbances such as persecution by humans. This is worrisome because changes in the density and distribution of apex predators can exert strong direct and indirect ecological effects that cascade through an entire ecosystem. However, our knowledge of these indirect ecological effects is still limited, particularly in marine environments. Coral reefs are one of the most diverse ecosystems, providing a useful model system for investigating the ecological role of apex predators and their indirect influence on lower trophic levels. In our work “Not worth the risk: apex predators suppress herbivory on coral reefs”, conducted on Lizard Island in the Great Barrier Reef (Fig. 1), we examined the indirect effects of two species of apex predators, a reef shark and large-bodied coral-grouper, on herbivore foraging we behaviour.

Figure 1. Location of study site

Using a novel approach of mimic predator models (Fig. 2) and GoPro video cameras we show that in the presence of an apex predator there is an almost localized cessation of algae consumption, due to the perceived risk of predation. Our work suggests that the indirect behavioural effects of apex predators on the foraging behaviour of herbivores may have flow-on effects on the functioning of coral reef ecosystems. This highlights that the ecological interactions and processes that contribute to ecosystem resilience may be more complex than previously understood.

 

Figure 2. Apex predator models. (a) Blacktip reef shark, (b) large coral-grouper and (c) small coral-grouper.

Picture below is of lead author Justin R. Rizzari (website: http://www.coralcoe.org.au/students/justin-rizzari)

 

The majority of pollination studies are performed in five countries, non of which in Africa. How does this bias affect application of the research in various geographic regions? Find out in the Forum paper in the April Issue of Oikos “Economic and ecological implications of geographic bias in pollinator ecology in the light of pollinator declines” by Ruth Archer and co-workers. Below is their summary of the paper:

Across much of the world pollinator loss has captured the attention of the media and the public.  In Europe pollinators regularly feature on the front page but here in southern Africa pollinator losses have received much less attention.  This doubtless reflects an underlying problem: in Africa, as across much of the world, we lack the data to record changing populations of pollinators or identify the threats facing them. 

In our opinion piece we aim to highlight that current understanding of pollinator losses (and more generally pollinator ecology) is based on data of comparatively narrow geographic scope.  More specifically, we show that almost half the data cited in thirteen recent meta-analyses, which ask important and diverse questions in pollination ecology, were collected in just five countries and Africa contributed only 4% of the data.  Does this matter?  Perhaps not, if the threats facing pollinators and responses to these challenges are similar across different regions, habitats and pollinator species.  However, this is unlikely.  There is enormous geographic variation in the distribution of anthropogenic disturbances, pests and parasites that are likely to impact negatively on pollinators.  For example, the Varroa mite, which is a major problem for European and North American honeybees, has less serious effects in subsaharan Africa and has not yet arrived in Australia.  Also, much more natural habitat remains in Africa than in Europe or America, although the speed of land use change is probably higher in Africa.  As pressures vary geographically, so too are different pollinators likely to vary in responses to them.  For example, subspecies of Apis mellifera differ in a suite of physiological and behavioural traits that make it unlikely that they will respond to ecological changes in the same way; therefore, management strategies designed around data collected on European honeybees may not be applicable to African subspecies.  Finally, from a socioeconomic perspective we need to better understand plant-pollinator interactions in understudied regions where the loss of pollination services could have immediate, dire effects: for example, where communities rely on subsistence farming or beekeeping for food security. 

If there are geographic gaps in our understanding of pollinator ecology and if these matter, what can we do about the issue given the socio-economic and logistical constraints that are likely responsible for much of this geographic bias?  In our article we offer solutions but, more importantly, hope to stimulate discussion on this important issue.  

Can hard-to-detect individuals of an endangered and declining population allow for testing of some of the major tenets of metapopulation theory while contributing to conservation efforts? A new multi-season occupancy model combined with observations on the Lower Keys marsh rabbit may have done just that. Read the Early View paper “Testing metapopulation concepts: effects of patch characteristics and neighborhood occupancy on the dynamics of an endangered lagomorph” by Mitchell J. Eaton and co-workers. below is their summary of the paper:

The Lower Keys marsh rabbit (LKMR, Sylvilagus palustris hefneri) is an endemic species found only on a handful of islands in the lower Florida Key islands. Following decades of decline caused by habitat fragmentation and degradation, sea-level rise and high rates of mortality inflicted by non-native predators, the LKMR was listed as endangered under the U.S. Endangered Species Act in 1990. Although several of these contributors to population decline have been improved, the distribution of the marsh rabbit continues to fall. With limited dispersal abilities, this secretive species persists in isolated habitat patches found within a highly fragmented landscape, challenging managers to identify viable solutions for their conservation and recovery. Given these conditions, a better understanding of the spatial aspects of marsh rabbit population dynamics could provide important insights and contribute to management efforts. We believed that a metapopulation framework would be the most useful for describing these dynamics. We were concerned, however, that existing metapopulation models were more theoretical than practical, based on too many assumptions and insufficient for dealing with the realities of a rare and hard-to-detect species. Therefore, we developed a new, flexible multi-season occupancy model that could test the concepts and assumptions of metapopulation theory, while investigating the dynamics of this species for the ultimate purpose of making recommendations for species management and recovery.

 Since its introduction in the 1960s, and following years of model development and application to natural systems, the theoretical underpinnings of metapopulation ecology have been strongly tied to assumptions about the relationship between neighboring patches, non-habitat (‘matrix’) characteristics and the probabilities of focal-patch extinction and colonization. Much recent work in metapopulation ecology has focused on developing advanced models that allow for incorporation of more detailed biological information to explain patterns in patch dynamics. Many of these models, however, have not taken into account the realities of imperfect detection in field sampling. As a result, only incomplete information on the abundance or occupancy levels of the surrounding landscape is available when making inference on the dynamics of a focal patch. As such, metapopulation models often rely on neighboring patch characteristics (e.g., perceived quality or size) as a proxy for the existence or abundance of colonizers and assume that local colonization will increase with patch connectivity. Local extinction probability has traditionally been modeled as a function of patch size, but is also predicted to be influenced by connectivity with neighboring habitat via a ‘rescue effect’. This latter process similarly depends on assumptions about the relationship between measurable patch characteristics and neighborhood occupancy, which can be difficult to quantify without consideration of the possibilities of non-detection.

 Building on recent advancements of the use of so-called ‘autologistic’ covariate models, we have developed a new multi-season occupancy model to explicitly incorporate estimates of neighborhood occupancy when modeling the dynamics of a metapopulation. Rather than treating the status or condition of a neighboring patch as certain (i.e., as a traditional, known covariate) we consider the occupancy of neighboring patches as an unobservable variable to be estimated. Our flexible model specification allows the ‘neighborhood’ to be defined in any number of ways, permitting nearly any a priori biological hypothesis to be tested. The model allows inclusion of a gradation of neighboring patch influence on the focal patch (e.g., habitat quality, distance, etc.) using patch-specific weights, as well as the quantification of non-habitat (e.g., water bodies) within the neighborhood. Using this modeling approach, we recast many of the assumptions of metapopulation theory as hypotheses to be tested explicitly.

 

Our results supported two of the major assumptions of metapopulation theory, namely that colonization probability is positively related to the occupancy of neighboring patches and that extinction probability is negatively related to local patch size. We also found support for the rescue effect, with extinction being mitigated by higher neighborhood occupancy, and for higher colonization rates being related to larger patch size. Model selection suggested that LKMR focal patch dynamics were influenced by a neighborhood effect size of approximately 1000m. Model results also suggest that patches in coastal areas (believed to be of higher quality for the species) experienced higher turnover rates than inland patches and that disturbance from sea-level rise, storm frequency and vegetation dynamics may be further destabilizing coastal patches. We found that lower-quality inland patches, which appear to be experiencing slower species turnover dynamics, may serve as refugia and provide an important source for colonization of coastal patches following local extinctions. Our findings can help managers better understand optimal spatial habitat configuration when planning restoration activities, predicted impacts of patch-specific removal of non-native predators and where translocations of LKMR would be most effective.

 

What are the roles of host phylogeny, transmission variables, and host traits in molding parasite metacommunity structure? Find out in the new Early View paper “Relative importance of host environment, transmission potential and host phylogeny to the structure of parasite metacommunities” by Ted Dallas and Steven J Presley. Here’s their own summary of the paper:

Identification of mechanisms that shape parasite community and metacommunity structures have important implications to host health,disease transmission,and the understanding of community assembly in general. In addition, a metacommunity approach can enhance the understanding of parasitological relationships among hosts, which may be reservoirs for emerging diseases or act as vectors that transmit diseases to humans or agriculturally important domestic animals.

 A metacommunity is typically defined as a set of ecological communities forming a network in space, such as  fish communities from a series of lakes across a landscape. However, Mihaljevic (2012) recently argued that metacommunity theory could be used to better understand parasite ecology. In our study, we considered host species to represent sites, with each host species harboring a distinct community of parasites. Each host species has a unique set of traits that define the environment for the parasites, the likelihood of parasite transmission to other host species, and the co-evolutionary relationships between hosts and their parasites.

 

 

 

Figure 1: Parasite distributions among rodent host species. Parasite group identity is indicated by color of the text in the graphic below the figure (e.g. Coccidians are in green).

 

We used data on rodent parasites from the Sevilleta Long Term Ecological Research Study to investigate parasite metacommunity structure from two perspectives. First, we used the Elements of Metacommunity Structure (EMS) framework to determine if parasite species distributions among hosts formed coherent structures (Leibold and Mikkelson 2002). Second, we assessed the relative roles of host phylogeny, host traits that can affect parasite transmission (e.g. home range size, diet breadth), and host traits that define the environment (e.g. body size, trophic status, longevity), using a variance partitioning analysis.

 Three distinct metacommunity structured occurred, Clementsian, quasi-Clementsian, and random. Despite the variation in structure,  host environment explained the largest proportion of the variation in community structure (~30%). This highlights the fact that no a priori relationship exists between particular structuring mechanisms and particular metacommunity structures. This suite of distinct responses from the same host metacommunity highlight the complex and diverse nature of host-parasite systems with respect to how parasites move through the environment, variation in life histories, and level of host specialization they exhibit. Mechanisms that contribute to parasite metacommunity structure may be highly complex, as host metacommunities can exhibit complex responses to local and spatial processes, with responses of hosts to large-scale environmental variation and responses of parasites to variation in host characteristics all contributing to parasite metacommunity dynamics.

 

Leibold, M. and Mikkelson, G. 2002. Coherence, species turnover, and boundary clumping: elements of meta-community structure. – Oikos 97: 237–250.

Mihaljevic, JR. Linking metacommunity theory and symbiont evolutionary ecology. Trends in Ecology & Evolution.

After more than 50 years of research into the ecology of large herbivores and predators in the greater Serengeti ecosystem, you might think that we know almost everything there is to know about this tropical savanna ecosystem. But in our article, “Episodic outbreaks of small mammals influence predator community dynamics in an East African savanna ecosystem” (Andrea E. Byrom et al.), we show that relatively little attention has focused on the role of small mammals (rodents and shrews) in tropical African savannas such as the Serengeti. This presents a critical gap in our understanding of one of Africa’s best known ecosystems.

Tropical savanna woodland, Serengeti National Park

We do know that in agricultural areas throughout East Africa, rodent populations fluctuate (outbreak) with large peaks in abundance, triggered by increased food availability during the dry season in response to the amount of rain in the preceding wet season. When outbreaks occur, species such as the multimammate rat Mastomys natalensis and the African grass rat Arvicanthis niloticus cause substantial economic damage in crop-growing areas. Before our study, however, little was known about the population dynamics of small mammals in tropical savanna, or their trophic importance, including as prey for some threatened carnivore species. Small mammals are a known food source for predators in this system, including mammalian carnivores in the weight range 1–18 kg, and birds of prey.

Arvicanthus niloticus, the African grass rat

It’s not surprising that researchers travel from all over the world to study an ecosystem as diverse and well-known as the Serengeti. Our team comprised researchers from Tanzania, New Zealand, Australia, the USA, Canada, and the UK – all scientists who had lived or worked in East Africa. Some of us have never met, but we all contributed to collection of the data that were used in this article. We pieced together a 42-year time series (1968-2010) on the abundance of 37 species of small mammals, derived from intermittent measures collected in Serengeti National Park and adjacent agricultural areas. Data on abundance of black-shouldered kites (1968–2010), eight other species of rodent-eating birds (1997–2010), and 10 mammalian carnivore species (1993–2010) were also collated.

Black-chested snake eagle, Circaetus pectoralis

We used climatic fluctuations and differences between unmodified and agricultural systems as perturbations to examine both bottom-up and top-down drivers of small mammal abundance: key to understanding responses to climate change and increasing human pressures adjacent to Serengeti National Park. Outbreaks occurred every 3–5 years in Serengeti National Park, with low or zero abundance of small mammals between peaks. There was a positive relationship between rainfall in the wet season and (a) small mammal abundance and (b) the probability of an outbreak, both of which increased with negative Southern Oscillation Index values. Rodent-eating birds and carnivores peaked 6–12 months after small mammals. In agricultural areas, abundance remained higher than in natural habitats.

 

The serval, Leptailurus serval

We conclude that small mammal outbreaks have strong cascading effects on predators in African savanna ecosystems. Changes in climate and land use may alter their future dynamics, with consequences for higher trophic levels, including threatened carnivores. Although outbreaks cause substantial damage to crops in agricultural areas, small mammals also play a vital role in maintaining some of the diversity and complexity found in African savanna ecosystems. Our study provides vital baseline data from which to monitor the future resilience of tropical savanna ecosystems.

 

The winner of the Global warming is – The long-tailed tit! Read more in the Early View paper “Climate change and annual survival in a temperate passerine: partitioning seasonal effects and predicting future patterns” by Philippa Gullet and colleagues. below is the press release, that at least have reached BBC News!

Climate change may be bad news for billions, but scientists at the University of Sheffield have discovered one unlikely winner – a tiny British bird, the long-tailed tit.

Like other small animals that live for only two or three years, these birds had until now been thought to die in large numbers during cold winters. New research published this week suggests that in recent years, weather during spring instead holds the key.

The findings come from a 20-year study of long-tailed tits run by Prof. Ben Hatchwell at the Department of Animal and Plant Sciences. The recent work is led by PhD student Philippa Gullett and Dr. Karl Evans from Sheffield, in collaboration with Rob Robinson from the British Trust for Ornithology.

“During spring, birds must work their socks off to raise their chicks,” said Philippa Gullett.

“For most small birds that live for only two or three years, not raising any chicks one year is a disaster. They might only get one more chance, so they can’t afford to fail.”

No surprise then that these birds are willing to invest everything and risk death if it means their young survive. The surprise is that weather makes all the difference. The research discovered that birds trying to breed in warm and dry springs have much better chances of surviving to the next year – a novel result that counters common assumptions about the cause of death for small birds.

“What seems to be going on is that the tits try to raise their chicks at any cost”, added Ms Gullett. “If it’s cold and wet in spring, that makes their job much tougher. Food is harder to find; eggs and chicks are at risk of getting cold. The result is that by the end of the breeding season, the adult birds are exhausted.”

The Sheffield team also found that despite no real effect of winter weather in recent years on adult survival, cold and wet autumns were associated with a higher death rate.

“We’re not saying that birds never die in winter – in harsh years there are bound to be some fatalities,” explains Dr. Karl Evans, supervising the research.

“However, it seems that in most years autumn weather plays a bigger role, perhaps acting as a filter that weeds out weaker birds before the real winter hits.”

Although autumns may get wetter in the coming years, any increase in mortality is likely to be offset by the benefits of warmer breeding seasons, when more benign

conditions reduce the costs of breeding.

Dr. Evans adds “Looking ahead to the future, our data suggest that every single plausible climate change scenario will lead to a further increase in long-tailed survival rates. While many species struggle to adjust to climate change, these delightful birds seem likely to be winners.”

The Rivelin Valley long-tailed tits featured in BBC’s Springwatch this year. To see the videos, go to:

http://www.bbc.co.uk/programmes/p01b7d6g – nest building behaviour

http://www.bbc.co.uk/programmes/p01bb1zf – chick provisioning and helping behaviour

What happens in the soil when forests are replaced by monocultures? Find out in the Early View paper “Habitat-specific positive and negative effects of soil biota on seedling growth in a fragmented tropical montane landscape” by Camila Pizano and co-workers. Below is the author’s summary of the study:

In this study we showed evidence that when montane tropical forests are replaced by monocultures of coffee and pasture grasses, plant-soil interactions change. Plant-soil interactions have been found to mediate the coexistence between plant species, and maintain biodiversity across a wide array of habitat types. However, we still have a poor understanding on how these interactions vary across neighboring habitat types dominated by different plant species. Furthermore, there are few studies on plant-soil interactions that have been done in both the greenhouse and the field.n this study we showed evidence from the greenhouse and the field that when montane tropical forests are replaced by monocultures of coffee and pasture grasses, plant-soil interactions change. Pastures accumulate soil organisms that are detrimental to pasture grasses and slow growing shade-tolerant tree species but are beneficial for fast growing, pioneer forest tree species. Forests accumulate soil organisms detrimental for pioneer species, but beneficial for slow growing, shade-tolerant forest tree species. And coffee plantations contain soil organisms that enhace the growth of pasture grass and pioneer forest tree species, but decrease the growth of shade-tolerant forest trees. These results suggest that the soil biota present in agricultural lands benefits primary sucession of montane tropical forests, but hinder the establishment of late sucessional forest species. Soil organisms in pastures also hinder the growth of pasture species that are important for cattle production.

How accurate are different forecast models for predicting population dynamics? That, and how predictable various animals actually are, was tested in the study “Complexity is costly: a meta-analysis of parametric and non-parametric methods for short-term population forecasting”,  by Eric J. Ward and colleagues, that is now published online in Oikos. Below is the author’s summary of the study:

Forecasting ecological data presents a unique set of challenges compared to other types of time series data (stock prices, weather) – two of the most common sources of uncertainty arise from (1) scientists not measuring populations perfectly, and (2) mechanisms responsible for population fluctuations are generally complex and not measureable at a population-wide scale (e.g. density dependence). Many ecological and fisheries models are made complex in an attempt to capture biological realism. Recent work on simulated and real datasets (Perretti et al. 2013 PNAS; Sugihara et al. 2012 Science) has shown that more accurate predictions can be made from simpler non-mechanistic models. Our paper presents the results of a forecasting competition, comparing a wide range of time series models to ~ 2400 time series, representing a range of vertebrate taxa. We found that in general, the best 1-5 year forecasts originated from simple models, such as a random walk (where the predicted population size is the current population size). Taxa that have strongly cyclic population dynamics, such as sockeye salmon, are the easiest to forecast, and warrant the use of more complex types of non-mechanistic models. Across all marine fish species, we found that longer lived species, or those with larger body size are easier to predict (presumably because they have smaller recruitment variability). Similarly, for birds, we found that higher trophic levels were also correlated with better predictions.

All of the time series included in our analysis were relatively long in ecology (25 continuous data points). The failure of many of the methods we considered suggests that improvement in forecasting ability is unlikley to come from better non-mechanistic forecasting methods or more annual population data; instead we recommend that efforts be made to better understand environmental drivers, which can be included as covariates.

Thanks to giant water bugs’ ferocious feeding habits and their extreme natural environment, authors Kate S. Boersma and colleagues, now have a greater understanding of how biological communities may respond to predator extinctions under increasing global environmental variability. All after having performed the study “Top predator removals have consistent effects on large species despite high environmental variability” published Early View in Oikos. below is their summary of the study and a presentation of the giant water bug.

We used the giant water bug system to explore the consistency of top predator effects in ecological communities that experience high local environmental variability. We experimentally removed giant water bugs from arid-land stream pool mesocosms in southeastern Arizona, USA, and measured natural background environmental conditions. We inoculated mesocosms with aquatic invertebrates from local streams, removed giant water bugs from half of the mesocosms as a treatment, and measured community divergence at the end of the summer dry season. We repeated the experiment in two consecutive years, which represented two very different biotic and abiotic environments. We found that giant water bug removal consistently affected large-bodied species in both years, increasing the abundance of mesopredators and decreasing the abundance of detritivores, even though the identity of these species varied between years. Our findings highlight the vulnerability of large taxa to top predator extirpations and suggest that the consistency of observed ecological patterns may be as important as their magnitude.

Giant water bug (Abedus herberti) consuming a dragonfly nymph (Oplonaeschna).

At ~3cm in length, giant water bugs (Abedus herberti) may appear unlikely top predators. Yet these aquatic invertebrates dominate the food webs of many small headwater streams in the arid southwestern United States. Giant water bugs use raptorial forelimbs to immobilize prey and piercing mouthparts to inject digestive enzymes and consume the liquefied tissue, allowing them to consume large vertebrate and invertebrate prey. These insects are flightless and thus highly vulnerable to changing hydrology caused by increasing droughts and anthropogenic water withdrawals in arid regions. Streams containing giant water bugs are characterized by seasonal flood/drought cycles and high natural environmental variability, making this an ideal study system to address fundamental questions about the relationship between predator loss and an increasingly variable abiotic environment.

“Which fruit should I eat?” – a decision both migratory and resident birds have to make over and over each autumn. This decision – and the consequences of it is studied in the Early View paper “Consistency and reciprocity of indirect interactions between tree species mediated by frugivorous birds” by Daniel Martinez and co-workers. Below is the authors’ summary of the paper:

Do fruiting plants compete or facilitate each other for frugivores providing seed dispersal? This question has been previously answered through single-species, short-term studies, that have evidenced indirect interactions between plants. Nevertheless this leaves unanswered another important question. How variable through time and across species within a community are these interactions? Resolving this question will help us to reveal the actual relevance of these interactions in natural systems.

Our study was developed in a straightforward plant-frugivore system. Three species of fleshy-fruited trees (hawthorn Crataegus monogyna, holly Ilex aquifolium and yew Taxus baccata) coexist in the secondary forest of the Cantabrian mountain range (NW Spain). Their seeds are mainly dispersed by a common assemblage of frugivorous blackbirds and thrushes (Turdus spp.). During autumn and winter both resident and wintering birds have to choose where to feed, among the fruiting trees belonging to the three plant species. Decisions are taken not only considering a given individual tree, but also the trees standing in its neighborhood, with the aim of optimizing in which to perch.

Far from general patterns of competition and/or facilitation between these tree species, we find that, like often in nature, variability seems to be the rule. The arising of indirect interactions and their sign shifted between species and across years.  Plant-frugivore systems, even those simple like this, are functionally complex. The abundance and spatial distribution of fruits changed from year to year. While some tree species increased their crops other became scarce. Birds faced very different fruiting scenarios every autumn and, thus, the costs and profits of feeding on different trees changed from year to year.

We do not attempt to explain the rules driving indirect interactions within a community, but to show their complexity, consistency between years and reciprocity between species. Taking this variability into account is crucial to understand the role of indirect interactions in the structuring of natural communities.

Artwork and photo credits: Daniel Martínez.

Ecosystem engineering, the physical modification of the environment by organisms, may well be the most common kind of non-trophic interaction – nearly as ubiquitous as eating and being eaten, and often as influential. Because species are affected by the physical environment, and because all ecosystem engineers belong to food webs while also modifying the environment, their dual role is potentially one of the most important bridges between the trophic and non-trophic. For example, many ant species are predators and important earth movers (see picture). Nevertheless, research in both areas has remained largely independent.

An upcoming paper (“Integrating ecosystem engineering and food webs” by D. Sanders, C.  Jones, E. Thébault, T. Bouma, T. van der Heide, J. van Belzen, and S. Barot) explores how to integrate ecosystem engineering and food webs. The paper provides rationales justifying integration, and then a framework for understanding how engineering can affect food webs and vice-versa, and how feedbacks alter dynamics. A simple food chain model is then used to illustrate the dynamics in the presence and absence of extrinsic environmental perturbations. The paper argues that current understanding of how engineering shapes food webs and vice versa is perhaps more hampered by lack of knowledge about food web responses to abiotic change than knowledge about how ecosystem engineers can cause such change; and that this is compounded by the fact that engineering and food web studies are rarely studied together in the same system. The authors argue that with appropriate studies and integrative models, conjunction is achievable, helping pave the way to a more general understanding of interaction webs in nature.

Ecosystem engineering and predation by Formica ants (photo credit Dirk Sanders)

What will happen at the meta-community level with all exposure to human activities in various ecosystems? To answer this, Anne Teyssèdre and Alexandre Robert have simulated a few alternative, presented in the Early View study “Contrasting effects of habitat reduction, conversion and alteration on neutral and non neutral biological communities”

Below is the author’s summary of the paper:

How can we explain the local coexistence of numerous ecologically similar species in the same trophic level communities (like plant, perching bird, or rodent communities), and how will these communities react to the current massive global habitat changes driven by human activities?

While these two questions are necessarily linked, scientists’ current answers seem contradictory. On one hand, Hubbell’s (2001) neutral theory of biogeography and biodiversity (NTB) succeeds to explain – and even predict – many community patterns observed and measured by biologists and biogeographers for several decades, among which the well-known “Arrhenius law”, or power law species-area relationship (SAR). [First proposed by Arrhenius in 1921, this empiric ‘law’ relates the richness at equilibrium (S) of a same trophic level community, in number of species, to the area (A) it occupies, in a power relationship: S = c.A^z]

Hubbell’s NTB assumes that the small ecological differences among the species composing a community can be neglected confronted to the large stochasticity (i.e. randomness) of local colonization, reproduction, extirpation and speciation events. It assumes the ecological and demographic equivalence of all species in the community at a local scale, in other terms. But this assumption clearly contradicts many biological and evolutionary data, among which the mere fact of evolution by natural selection. [Hubbel’s neutral model must hence be considered as a useful null hypothesis to confront other community dynamics models, and to explore the correlates of “ecological drift”, like Kimura’ s neutral theory of genetic evolution may be used to explore the correlates of genetic drift.]

To tackle this intriguing issue, we modeled the dynamics of different species communities confronted to different types of habitat changes. More explicitly, we defined a small number of species categories differing in their level of specialization to different habitat types and explored the impact of different simulated habitat changes on a regional community mixing generalist and specialist species (specialization model), compared to that of a community composed of ecologically equivalent species (neutral model), combining stochastic, deterministic and selective processes.

We noteworthy found that (i) both models ruled with habitat reduction predict an approximately power law SAR, in conformity with empirical observations; (ii) with the specialization model, but not with the neutral one, habitat conversion (i.e. land use change) and alteration (e.g. aridification, acidification, eutrophization…) may increase regional species richness until a threshold; (iii) habitat alteration, with the specialization model, leads to the rarefaction of specialist species and the expansion of generalist species, i.e. to the functional homogenization of the community at local and regional scale.

While not predicted by the NTB, these two later patterns are currently observed in many local or regional communities confronted to habitat changes.  We conclude that this kind of model mixing a few stochastic, deterministic and selective processes may be use to explore and anticipate the dynamics and biodiversity patterns of living communities at different geographic scales, in response to different environmental strategies and scenarios.

Now on Early View: A study about functional traits in Sphagnum and how it affects carbon cycling. “Tradeoffs and scaling of functional traits in Sphagnum as drivers of carbon cycling in peatlands” by C.G. Laing and co-workers. Below is the author’s own summary of the study:

The effect of temperature on the decomposition of vegetation has been extensively studied within the climate debate. However, the functional traits of vascular plants have been shown to strongly effect decomposability independently of temperature.

Our study  in Oikos explored whether functional traits could explain decomposition of the peat-forming moss Sphagnum since its growth plays a substantial role in global carbon storage.  We coupled classical approaches with the first allometric scaling calculations for Sphagnum to identify water and light availability as controls on growth strategy that impact decomposition rates. It is our hope that our fellow researchers will test the scaling relationships developed here further.

Image: Sample collection 07-09-2010 on Ryggmossen Bog, Sweden

If many mouths eat a lot of a not so preferable foot item – i.e. large numbers of city rats happen to live underground where they only have access to garbage-like food items – this does not tell us that another foot item not accessible to the crowd is genuinely much more preferable – which rat would refuse to snack on gourmet cheese if there wouldn’t be obstacles that allow only brave foragers to have a bite on it?

In ecological network studies, species preferences are often summarized as to how often species interact with each other for multiple species.  This can be foragers feeding on different resources, for example.

While indices and summary statistics for explaining resulting network structure have experienced much sophistication in recent years, the fact that interaction frequencies are the product of preferences / attraction towards interacting partners and availability / abundance of interacting species has received little attention.

The early view paper “Population fluctuations affect inference in ecological networks of multi-species interactions” by Konstans Wells and co-workers, shows that population fluctuations have considerable impact on calculated network statistics. So an increasingly large range of values can be inferred from the same ecological system the more populations fluctuate.  Considering  abundance fluctuations and sampling effort in ecological networks may not only improve inference, but also open promising perspectives to novel questions in ecological research  – certainly if the crowd makes it to the most preferable piece of meal, this will affect all aspects from individual behaviour to what is left on the plate for the next round of interactions, be it for single species or communities.

How different kinds of ecological aspects affect the future of invasive plants is studied in the Early View paper:“Neighborhood-contingent indirect interactions between native and exotic plants: multiple shared pollinators mediate reproductive success during invasions” by Susan Waters and co-workers. Below is the author’s summary of the study:

In the highly fragmented prairies of western Washington’s Puget Trough, conservation focuses on managing invasive plant species that may directly compete with rare native forbs.  However, the area also has a depauperate pollinator community, and the highly overlapping assemblage of generalist pollinators visiting native and exotic dandelion-like forbs suggested to us that native and exotic plants might also interact indirectly through pollinators (for example, by competing for pollinator visits, or by altering the amount of conspecific pollen transferred to a neighbor). 

Given that one of the dominant invaders, Hypochaeris radicata, has a patchy distribution, and that pollinators often alter their foraging patterns in response to floral density, we speculated that pollinator-mediated indirect interactions might play out differently in H. radicata-dominated floral neighborhoods than in less-invaded, more diverse floral neighborhoods. 

However, further observation soon caused us to suspect that the story was more complex. There were multiple pollinator intermediaries between the plants, and we realized that pollinator groups might differ in their responses to different floral neighborhoods. We hypothesized that there were at least two ways that floral neighborhoods might alter pollinator behavior: either by changing whether pollinators chose to forage in the patch at all, or by changing the foraging decisions pollinators made once they arrived in the patch.

We compared pollinator visitation and seed set by two native forbs and H. radicata in three floral neighborhoods: high density native (and low density H. radicata), high density H. radicata (and low density native) and low density of both H. radicata and natives. Eusocial bees, solitary bees, and syrphid flies all visited the H. radicata and the two native forbs we observed, but the proportion of total visitation to a plant species from each pollinator group depended on the floral neighborhood.  Accordingly, dense exotic H. radicata neighborhoods facilitated seed set in one native forb, Eriophyllum lanatum, while diminishing seed set in another native forb, Microseris laciniata.  Context-dependent pollinator visitation, mediated by multiple pollinators, thus resulted in opposing effects of an exotic plant on two native species.

We’re very happy to welcome Dr Martijn Bezemer, NIOO-KNAW, the Netherlands to our editorial board.

Martijn, what’s your main research focus at the moment?
My main research focus is on aboveground-belowground interactions. I study how (i) soil biota (ii) manipulations of the soil community, and (iii) soil mediated effects of neighbouring plants affect the nutritional quality of focal plants and the aboveground plant-insect interactions on those focal plants. Further, I study the role of soil organisms in restoration of grasslands on former arable land. Much of this work is carried out in the field.

Can you describe you research career?

My MSc was in Crop Protection in Wageningen, The Netherlands. I started my carreer at Imperial College at Silwood park, where I studied the effects of elevated CO2 and elevated temperature on plants, insects and parasitoids in model ecosystems in the ecotron controlled environment facility. This was from 1995 to 1999. From 1999 to 2000 I went to UC Berkeley for a post-doc. Here I studied biological control of codling moth in walnut orchards using introduced parasitoids. In nov 2000 I moved back to the Netherlands for a post doc at the Netherlands Institute of Ecology (NIOO). I first studied the effects of root herbivory by wireworms on aboveground plant-insect interactions in cotton and then worked on the effects of aboveground and belowground multitrophic interactions on plant diversity and succession. In 2004 I moved to Wageningen University but continued working on linking aboveground and belowground diversity. In 2008 I am moved back to the NIOO, and I have a position as senior scientist.

How come that you became a scientist in ecology?

During my MSc I focused agronomy. My stay at Silwood Park made me an ecologist.

What do you do when you’re not working?

I like to play guitar, read literature and DIY type activities in our house

For the February and March issue we have selected three articles as Editor’s choices that are currently open access. We selected papers that are at the heart of our publication mission, so papers that aim at providing synthesis in ecology. The work by Sergio Estay and colleagues focusses on the role of temperature variability for insect performance, and how these individual changes in performance feedback on population dynamics. The work is theory-based and provides a framework to organize research of the role that thermal mean and variability plays in individual performance, and how it may affect population dynamics. By developing null models, they demonstrate that potential changes in the intrinsic population growth rate depend on the interaction of mean temperature and thermal variability, and that the net effect of the interaction could be synergistic or antagonistic. The theoretical models are evaluated using data compiled from literature.

A promising avenue to test these theoretical predictions is using experimental microcosms. While it remains questionable to which degree such small-scale studies scale up to macroscopic patterns, they allow a tight coupling between simple models and real data that are collected in a standardized manner. Clements and colleagues followed this approach to test the effects of directional environmental change on extinction dynamics in experimental microbial communities as predicted by a simple model. Based on the assumption that temperature does alter an individual’s metabolic rate, and consequently birth and death rates, they predict that in declining populations, these alterations may manifest as changes in the rate of that population’s decline, and subsequently the timing of extinction events. Clements and colleagues find that extinction occurs earlier in environments that warm faster, and importantly that phenomenon can be accurately predicted by a simple metabolic model. Increasing the number of parameters that were temperature-dependent increased the model’s accuracy, as did scaling these temperature-dependent parameters.

 

The last Editor’s choice for now is the Per Brinck contribution from 2013 by Sharon Strauss: Ecological and evolutionary responses in complex communities: implications for invasions and eco-evolutionary feedbacks. In this contribution, Strauss discusses our current understanding on how interactions between ecological and evolutionary dynamics affect the organization and functioning of simple and more complex communities. Based on her own work and that of many others, she examines how community complexity may influence the nature and magnitude of these eco-evolutionary feedbacks, and how an escape from community complexity per se affects the success of invaders. She synthesizes the diverse dynamics into three general types: those generating alternative stable states, cyclic dynamics, and those maintaining ecological stasis and stability.

 

How does grazing affect the soil? Find out in the Early View paper “Grazing-induced changes in plant–soil feedback alter plant biomass allocation” by Ciska van Veen and co-workers.

Cows and rabbits, feed on plants. With that they change plant growth directly, for example by removing leaves. In addition they may change an array of soil conditions, such as the amount of nutrients or root feeders in the soil. In this study we found that these changes in the soil from grazed grasslands influenced plant growth (photo 1).

Photo 1: greenhouse experiment where the researchers investigate the growth of different plant species in soils from grazed and ungrazed grasslands.

However, the impact of cows and rabbits on plant growth via changes in the soil, did not help us to understand the species composition of plants in the field (photo 2). Thus, the direct influence of cows and rabbits on plant growth seems more important for plants in the field.

Photo 2: field experiment in the Junner Koeland Nature Reserve (the Netherlands). Cows and rabbits are excluded with fences from parts of the nature reserve. The researchers used the soil from inside and outside the fences to test the response of plant species. In addition, the researchers monitored the plant species composition inside and outside the fences to test if the response of the plants to the different soils could help to understand the plant species composition.

Recently, Wiley released the list over most downloaded Oikos papers during 2013. Many of the papers are familiar titles, that were published a few years ago. However, two of the papers published during 2013 actually managed to climb the ladder and take place among the top ten. Both of them were presented at this blog. Both of them were selected as Editor’s choice.

Here’s a link to the top 10 list:

http://onlinelibrary.wiley.com/journal/10.1111/(ISSN)1600-0706/homepage/MostAccessed.html

The two 2013 papers have been opened for Free Download by Wiley for the next two weeks, so take your chance to download them today! And the papers are:

Is the Oikos chief editor the only one working? Dries is busy handling manuscripts while James and Maria dream of seeds and eagle owls, respectively!

Dispersal and species’ responses to climate change with 1384 downloads

by J. Travis et al.

Link to paper: http://onlinelibrary.wiley.com/doi/10.1111/j.1600-0706.2013.00399.x/full

Link to blogpost: https://oikosjournal.wordpress.com/2013/09/13/dispersal-at-the-heart-of-our-thinking/

and

The elephant in the room: the role of failed invasions in understanding invasion biology with 1604 downloads

by Zenni and Nunez

Link to paper: http://onlinelibrary.wiley.com/doi/10.1111/j.1600-0706.2012.00254.x/full

Link to blogpost: https://oikosjournal.wordpress.com/2013/02/01/the-elephant-in-the-room/

A hybridization event at the bottom of the food chain may affect organisms several steps up the chain. Read more in the early View paper: “Bottom–up regulates top–down: the effects of hybridization of grass endophytes on an aphid herbivore and its generalist predator” by Susanna Saari et al. 

Below is their popular summary of the study:

Hybridization is a well understood process where organisms fuse to form new organisms with unique characteristics. However, the ecological consequences of hybridization in the microbial partners of plants are largely unknown. We studied the effects of hybridization of microbial plant symbionts on the feeding preference and performance of herbivores and their natural enemies. In our laboratory experiments, we used the grass Arizona fescue as the host plant, Neotyphodium endophyte as the microbial plant symbiont, the bird cherry-oat aphid as the herbivore and the pink spotted ladybird beetle as the predator. Neither endophyte infection (infected or not infected) nor hybrid status (hybrid or non-hybrid) of the endophyte affected aphid reproduction, aphid host plant preference or body mass of the ladybirds. However, development of ladybird larvae was delayed when fed with aphids grown on hybrid endophyte infected fescue compared to ladybird larvae fed with aphids reared on either non-hybrid infected fescue, non-hybrid, endophyte-removed fescue and hybrid, endophyte-removed fescue.

A pink spotted ladybird and bird cherry-oat aphids on Arizona fescue. In our experiment, pink spotted ladybirds avoided aphids that had been feeding on grasses infected with hybrid Neotyphodium endophytes.

Furthermore, adult ladybrids were more likely to choose all other types of fescues harboring aphids rather than hybrid endophyte infected fescues. Our results suggest that the hybridization of microbial symbionts may negatively affect predators such as the pink spotted ladybird and protect herbivores like the bird cherry-oat aphids from predation even though the direct effects on herbivores are not evident.

Neotyphodium endophyte (red lines) growing between the cells (the red circles) of a plant. Endophytes are micro-organisms growing within the tissues of plants without causing any symptoms for the host. Some fungal endophytes can fuse with other fungi growing within the tissues of the host plant thereby forming a hybrid fungus with unique characteristics.

Ecological synthesis is tricky. One of its many challenges is that empirical data rarely paint a clear picture either supporting or refuting a given hypothesis. More typically, empirical studies have diverging results. But even for hypotheses where refuting evidence is overwhelming, ecologists are often reluctant to abandon them (see Oikos Blog on Zombie Ideas).

In our paper “The enemy release hypothesis as a hierarchy of hypotheses” (Heger & Jeschke in Oikos, early view), we explore a novel method for assessing ecological hypotheses based on empirical evidence: the Hierarchy-of-Hypotheses (HoH) approach. This approach was born during a joint project (see Jeschke et al. 2012 in Neobiota) and a workshop titled ‘‘Tackling the emerging crisis of invasion biology: How can ecological theory, experiments, and field studies be combined to achieve major progress?’’ (see Heger et al. 2013 in Ambio). When we discussed the problem of imprecise formulations of hypotheses in invasion ecology (another challenge to ecological synthesis), it became obvious that we need a framework for integrating both broad and narrow hypotheses. Our suggestion for such a framework is the HoH approach, where a broad, overarching hypothesis branches into increasingly narrow and specific formulations of this hypothesis (i.e. sub-hypotheses). The most specific formulations are empirically testable.

The HoH approach can serve as an organizational tool (e.g. to structure research questions, or to organize conceptual work), but also for assessing hypotheses. In our paper, we show the first worked-out example for a HoH. We used the method for a well-known and much discussed hypothesis of invasion ecology: the enemy release hypothesis. Applying a newly developed weighting procedure, we assessed empirical evidence for each sub-hypothesis. Our results show that overall, there is nearly as much evidence in favor as against the enemy release hypothesis; hence, the overall picture is quite blurry. However, a closer look at the sub-hypotheses reveals that specific formulations of the enemy release hypothesis are clearly empirically supported, whereas other formulations receive hardly any support (see Fig. 1). This example shows how powerful the HoH approach can be to make a blurry picture clear.

 

Figure 1. Schematic illustration of a hierarchy of hypotheses (HoH) for the enemy release hypothesis. The scheme classifies empirical tests of the enemy release hypothesis according to three criteria, shown as three hierarchical levels: (1) indicator for enemy release; (2) type of comparison; and (3) type of enemies. The combination of these criteria results in different sub-hypotheses which are drawn as boxes; the number of empirical tests available for each sub-hypothesis is given in the respective box (‘n’). The boxes are color-coded as follows: red boxes: 50% or more of the data question the sub-hypothesis, and n≥5; green boxes: 50% or more of the data support the sub-hypothesis, and n≥5; white boxes: all other cases (i.e. n<5 or inconclusive data).

In writing the paper, we had several discussions on how much empirical support is needed to call a hypothesis ‘supported’. For Fig. 1, we agreed on the threshold of 50% support, but this is debatable. We believe that ecology needs a discussion on these questions: How do we decide whether a hypothesis is worth keeping? How much supporting evidence is needed, and how much refuting evidence can be tolerated? We very much hope that our paper stimulates discussions on these and similar questions. Also, it would be great to see more HoHs being created, in ecology and beyond.

Tina Heger & Jonathan M. Jeschke

Last week, the annual Oikos meeting was held in Stockholm. This year as a Nordic event, with speakers from both Sweden, Norway, Denmark, Finland and Iceland.

The big happening was of course, that Prof. Bob Holt was awarded the Per Brink award.

Bob gave a fantastic talk, managing to turn theoretical ecology to an exciting fairytale!

After the talk, Oikos’ Editor in Chief, Dries Bonte and Managing Editor, Åsa Langefors (on the photo) handed over the diploma and the glass apple.

The diploma is a wonderful piece of artwork, painted by biologist and artist Linnea Fredriksson http://linnea.linneaartline.com Linnea reads most of the awardee’s scientific work and uses the study species and focus to create the picture.

Take a closer look at Bob’s diploma:

Congratulations Bob! http://people.biology.ufl.edu/rdholt/

Why might you find scientists out on a pitch black night on a remote Alaskan lake driving two 18’ boats with a net towed in between?  Fun, tradition, data collection?   Well, all of the above, assuming the weather is nice.  In our article, “Climate variation is filtered differently among lakes to influence growth of juvenile sockeye salmon in an Alaskan watershed,” we rely on generations of scientists doing just this to evaluate how juvenile salmon growth responds to climate variability.

Long-term datasets provide opportunities to disentangled pattern from noise.  Establishing and maintaining long-term datasets requires marshalling the human, financial, and logistical support necessary to return year after year to collect data.  The University of Washington’s Alaska Salmon Program (http://fish.washington.edu/research/alaska/ or https://www.facebook.com/AlaskaSalmonProgramFRI) has been sending scientists to remote southwest Alaska since the mid-1940s to collect data on juvenile sockeye salmon and their habitats.

Our field methods today are remarkably similar to those established over 60 years ago.  Every summer at the end of August, we head out onto our study lakes (in this case, Chignik and Black lakes) on small boats just as the sun is heading down.  Armed with a net that looks a like a gigantic windsock with arms, flashlights, a GPS, and trays and buckets, we get ready to capture and measure juvenile sockeye salmon.  Juvenile sockeye salmon feed near the surface at night making them more easily sampled by our nets.  We tow the net between our “master” and “slave” boats according predetermined tracks, hoping to steer far clear of shore.  After towing for a set time, we haul in the net and inspect our catch.  Fish we catch are subsampled and brought back to our field station to be measured and weighed.

By sampling year after year, we can observe the variation in juvenile sockeye salmon growth during their first summer of life and evaluate causes of variation in growth.  Growth is an important determent of their ability to avoid predators as well as survive winter conditions and ocean migration.  In our study we investigated if the year to year variability in growth was explained by climate variation, including differences among years in winter and spring air temperature.  Using additional information regarding juvenile salmon growth collected from adult sockeye scales, we were also able to investigate whether the same regional climate such as air temperature elicits the same growth response from juvenile salmon in different lake types.

We found that the average size of juvenile salmon has been increasing over time.  However, the same changes in air temperatures did not always lead to the same response in juvenile salmon growth in different lake types.  Juvenile sockeye salmon grew larger in years with warmer spring and fall temperatures in deep, cold Chignik Lake.  Just upstream in shallow, warm Black Lake, juvenile salmon grew less in years with warmer air temperatures.  These differences in growth indicate that landscape diversity within watersheds filters climate such that organisms experience and respond differently among habitats. Our ability to manage for resilient ecosystems in the face of ongoing environmental change may be improved by considering within, as well as among, watershed climate filtering.

Having one predator chasing you is scary enough, but what about having two? Hunting in different habitats? Lucky me not being  roe-deer! Read more in the Oikos Early View paper “Living and dying in a multi-predator landscape of fear: roe deer are squeezed by contrasting pattern of predation risk imposed by lynx and humans” by Karen Lone and colleagues. Below is Karen’s summary of the paper:

The challenge of managing large carnivores in a multiple-use landscape in Norway has motivated a large research effort to understand carnivore ecology and their impact on livestock and other wildlife, in addition to extensive monitoring. I was lucky to be able to use some of the data collected in this larger framework to investigate predator-prey interactions and the landscapes of risk for roe deer. Our goal was to look at the effect of multiple predators preying on a single prey species. Roe deer have a natural predator in lynx, and a functional predator in hunters. We investigated how predation risk from these two predators related with habitat characteristics by comparing kill sites to sites used by live roe deer, and anticipated that they produced conflicting landscapes of risk.

LiDAR data from one field plot with radius ca 28m in a 3D perspective – points are colored by height above the ground, so vegetation hits stand out in warmer colors than ground hits.

In this paper we try to use Light Detection and Ranging (LiDAR) data to predict risk. We had access to a LiDAR dataset obtained by airborne laser scanning the entire 900km² study area. As well as giving spatially extensive information, it also gives a lot of detail: the point cloud of height measurements (points at which laser beam was reflected) gives a nice visual impression of vegetation structure (see figure). Especially important LiDAR variables in our analysis of risk were laser echoes from the 0.5-2m height segment, corresponding to the density of the understory vegetation. The final predictive maps of predation risk are based on LiDAR data, a terrain model and a map of roads.

Our study site Hallingdalen, a valley in central Norway, is a multiple-use landscape.

Both LiDAR data and field data provided the same findings – that predation risk from lynx was higher in denser habitat, and increasing with distance from roads. Conversely, the risk of being killed by a hunter was higher in more open habitat and closer to roads, indicating that roe deer face a trade-off between the two predators along these gradients. With regards to some habitat characteristics, the risk gradient aligned for lynx and hunter – both inferred greater risk in more rugged terrain. From the spatial predictions, we found that only 1% of the area had low predation risk from both predators. In other words, when we considered two predators together rather than each on their own, the roe deer had almost no refuges where they can escape predation altogether. Our study raises questions of how roe deer adapt their behavior, if at all, to reconcile the risk landscapes they face, and whether the temporal variations between their two predators may be the key to avoiding mortality.

The first editor’schoice for 2014 is the work of Alexander Kubisch and colleagues. This invited contribution synthesizes how feedbacks between ecological and evolutionary on dispersal shape species ranges and range dynamics. The manuscript is a systematic review on the existing literature and prevailing insights combined with novel modeling approaches to demonstrate the relevance of evolutionary forces at all hierarchical levels of biological organization (from landscapes to communities via populations, individuals and genes) that affect distribution ranges. Since Oikos has been publishing many relevant key-papers in this field, the authors have additionally compiled a virtual issue which will be available in January and which is introduced here. Alexander Kubisch won the Horst-Wiehe-prize at the GfÖ annual meeting for this synthesizing range biology work.

Synthesis: What factors are responsible for the dynamics of species’ ranges? Answering this question has never been more important than today, in the light of rapid environmental changes. Surprisingly, the ecological and evolutionary dynamics of dispersal – which represent the driving forces behind range formation – have rarely been considered in this context. We here present a framework that closes this gap. Dispersal evolution may be responsible for highly complex and non-trivial range dynamics. In order to understand these, and possibly provide projections of future range positions, it is crucial to take the ecological and evolutionary dynamics of dispersal into account.

The second editor’s choice for January is the research paper by Qi and colleagues. They analysed a large trait database involving 1355 species from the northeastern verge of the Tibetan Plateau to test to which degree seed mass is affected by changing abiotic conditions along altitudinal gradients. The analysis of such a large dataset revealed the relevance of two opposing forces, stress tolerance and energy constraints. Subsequently, life history cycles, resource allocation strategies and dispersal agents appeared to be more important drivers in seed mass than pollination efficiency along a pronounced latitudinal gradient. Clearly, only an integrated analysis of the potential drivers of a single trait like seed size may lead to such comprehensive insights.

Synthesis: With increasing elevation, seed mass may be either larger for its advantage during seedling establishment (‘stress-tolerance’ force), or smaller owing to energy constraints. Our paper shows some novel and importance results in the seed mass–elevation relationship in a northeastern Tibetan flora. Firstly, these two opposing forces operate simultaneously but overall balance out one another. Secondly, the balance tends to shift toward increased energy-constraints (stress-tolerance) with the increase (decreased) in average seed mass. Thirdly, energy constraints on seed mass is indirect and mediated by the variation in plant height. Finally, plant resource allocation pattern, life-history cycle, and availability of dispersal agents can affect the responses of seed mass to elevation.

Dries Bonte

If  a vector prefers uninfected hosts or infected hosts – how does that affect the pathogen’s spread? Find out in the Early View paper “Vector preference and host defense against infection interact to determine disease dynamics” by Adam R. Zeilinger and Matthew P. Daugherty. Here’s a short version of the paper:

Pathogen spread is greatly influenced by the way that vectors choose which host to feed upon.  Epidemiologists have recognized that many vectors make feeding choices based on whether the host is infected with the pathogen or not.  For example, some mosquito species prefer to feed on animals (including humans) that are infected with malaria over malaria-free animals.  Conversely, the glassy-winged sharpshooter—which spreads the causal pathogen of Pierce’s disease among grapevines—prefers healthy plants.

At the same time, epidemiologists have also recognized that hosts vary in their susceptibility to a disease.  Some hosts are resistant to infection, meaning that the pathogen replicates poorly in them.  Other hosts are tolerant to the disease, meaning that the pathogen can replicate but the host simply does not express disease.  Resistance and tolerance are both forms of defense against a pathogen.

While vector feeding preference and host defense are clearly important for the spread of a pathogen, we were interested in understanding how the two factors may interact to influence pathogen spread.  To begin to understand the relationships between vector preference and host defense, we used a series of mathematical models, similar to SIR models widely used in epidemiology.  The models simulate the spread of a pathogen in interacting host and vector populations under different scenarios for vector preference and host defense.

We found that host resistance curbed pathogen spread, regardless of whether vectors preferred or avoided disease symptoms.  However, differences in vector behavior resulted in highly divergent effects if hosts were tolerant, with the greatest pathogen spread occurring if vectors avoided symptoms.  This occurs because, by masking infection, tolerance causes more vectors to inadvertently come into contact with infected hosts and acquire the pathogen.  Furthermore, we extended our model to a two-patch model, in which two host populations with differing defenses were connected by vector movement.  The outcomes from those scenarios support the idea that host defense impacts pathogen spillover, with a greater potential for tolerant host to be pathogen sources relative to resistant host types.

These results highlight the importance of understanding both vector feeding behavior and the precise form of host defense in predicting pathogen spread.  This may be particularly important for integrated disease management for agricultural crops.  For example, given that the glassy-winged sharpshooter prefers disease-free grapevines, breeding new grapevine varieties that are tolerant to Pierce’s disease may lead to unexpectedly high disease spread among nearby susceptible grapevine varieties.

It’s here! Our new webpage is ready and open for everyone to visit!

Apart from journal information, aims and scopes of Oikos and author guidelines for manuscript submissions, you also find, twitter- and facebook flows, abstracts to newly accepted papers as well as abstracts and links to Early View Papers. The latter with Altmetrics, an article’s impact on the web.

Welcome to visit us at www.oikosjournal.org

The online library is still found at http://onlinelibrary.wiley.com/journal/10.1111/%28ISSN%291600-0706

Submissions are still sent to http://mc.manuscriptcentral.com/oikos

Blog posts will appear both on oikosjournal.wordpress.com, where all old posts are found to, and on our new blog site http://www.oikosjournal.org/blog

We are very happy to announce that “The Per Brinck Oikos Award 2014” has been awarded to Professor Robert D. Holt, University of Florida, Gainsville, Florida, USA.

Here is Bob’s presentation of himself and his research:

“What makes the study of life such an endlessly satisfying endeavor is that species and ecosystems reflect both order and change – both the predictable outcome of general laws, and the lingering effects of idiosyncracies of evolution, earth history, and the often surprising feedbacks that arise in complex natural systems.  As a fan of natural history, I appreciate and indeed relish the complexities and unique contingencies of ecological systems, even as in my role as theoretician I seek for unifying principles.  I have carried out research on a wide range of topics, from food web dynamics and host-pathogen interactions, to habitat fragmentation, to the evolution of dispersal and geographical ranges, and have had the good fortune to have collaborated over my career with many outstanding theoreticians and empiricists.  But in my own mind underlying this diversity of specific topics there is a thematic unity, involving on the one hand a concern with teasing apart the forces driving complex ecological systems, and on the other the desire to integrate perspectives from different disciplines, such as evolution, dynamical systems, and behavior, into our understanding of ecological systems. One approach to ecological complexity is to closely examine the direct and indirect interactions among a small number of interacting species – community modules – which can reveal processes at play in much richer webs of interactions.  Another is to recognize the pervasive influence of spatial heterogeneity and dynamics for almost all ecological systems.  Yet another approach is to recognize the intertwining of ecology and evolution.  For example some taxa are very conservative in their ecological niches, whereas others can evolve rapidly and even explosively over short time horizons.  Understanding all these aspects of ecological complexity, and how they are related over both short and long time-scales, is crucial for addressing a wide range of applied problems, from keeping in check invasive species and emerging diseases, to conserving species in altered landscape, to predicting the impacts of climate change.”

The Per Brinck Oikos Award recognizes extraordinary and important contributions to the science of ecology. Particular emphasis is given to scientific work aimed at synthesis that has lead to novel and original research in unexplorered or neglected fields, or to bridging gaps between ecological disciplines. Such achievements typically require theoretical innovation and development as well as imaginative observational or experimental work, all of which will be valid grounds for recognition.

The /Per Brinck Oikos Award/ is delivered in honor of the Swedish ecologist Professor Per Brinck who has played an instrumental role for the development and recognition of the science of ecology in the Nordic countries, especially as serving as the Editor-in-Chief for Oikos for many years.

The award is delivered annually and the laureate receives a modest prize sum (currently €1500), a diploma and a Swedish artisan glassware. The prize ceremony is hosted by the Swedish Oikos Society. The award is sponsored by the Per Brinck Foundation at the editorial office of the journal Oikos and Wiley/Blackwell Publishing.

Per Brink passed away, at the age of 94 years a few months ago. Read the memorial in Oikos here.

How is lake water quality and nutrient fluxes effected by invasive and native organisms? That’s what Geraldine Nogaro and Alan D. Steinman are answering in the new Early View Oikos paper, “Influence of ecosystem engineers on ecosystem processes is mediated by lake sediment properties”.

Here’s the author’s summary of the paper:

Dreissenid mussels, an iconic invasive species of the Laurentian Great Lakes since their introduction via ballast water in the late 1980s, can greatly alter nutrient fluxes and the microbial food web through their filter-feeding activity and excretion of feces and pseudo-feces at the water–sediment interface. Invasive species may impact biotic community structure, ecosystem processes, and associated goods and services. Their impacts may be especially strong because they also serve as ecosystem engineers (i.e., organisms affecting the physical habitat and resources for other species). The main objective of our study was to determine how the filtering/excretion activity of invasive mussels and the burrowing/bioirrigation activity of native chironomid larvae affect nutrient fluxes and water quality in Muskegon and Bear Lakes (Fig. 1). Laboratory mesocosm experiments were conducted using core tubes filled with sediment, water, and invertebrates (mussels and chironomids) collected from Muskegon and Bear Lakes (Fig. 2).

Fig. 1. Location of Muskegon and Bear Lakes within Laurentian Great Lakes region in Michigan, USA (top). Muskegon Lake (bottom left) and Bear Lake (bottom right) from the sampling boat.

Fig. 2. Dr. Geraldine Nogaro sieving sediment from Muskegon Lake to collect burrowing macroinvertebrates and study their influence on nutrient biogeochemistry in impacted lake ecosystems.

Results showed that sediment reworking and ventilation activities by chironomids increased oxygen penetration in the sediment, affecting primarily pore water chemistry, whereas invasive mussels enhanced nutrient releases in the surface water (Fig. 3). However, burrowing chironomids had a greater influence on sediment reworking and microbial-mediated processes in organic-rich sediments (Bear Lake), whereas invasive mussels enhanced nutrient concentrations in the overlying water of organic-poor sediments (Muskegon Lake). These results have management implications, as the effects of invasive mussels on the biogeochemical functioning in the Great Lakes region and elsewhere can alter system bioenergetics and promote harmful algal blooms.

Fig. 3. Sediment cores used to evaluate invertebrate effects on nutrient release (top). Native chironomids created oxygenated burrows (bottom left), while invasive mussels stimulated nutrient release at the sediment surface (bottom right).

Reference:

Nogaro G., Steinman A.D. (2013) Influence of ecosystem engineers on ecosystem processes is mediated by lake sediment properties. Oikos doi: 10.1111/j.1600-0706.2013.00978.x

How does fruit-eating relate to body size and geographic range? Find out in the Early View paper “Ecological correlates of trophic status and frugivory in neotropical primates” by Joseph E. Hawes and Carlos A. Peres.

Below is their summary of the study:

A good understanding of non-human primate diets in the wild is vitally important for the conservation planning of threatened species, with forest habitat loss and severe forest degradation a major concern throughout the New World tropics. It is also critical to help evaluate the roles of primates within forest food webs, particularly as seed dispersers for tropical forest plants. Fruit eating is widespread amongst primates although they are rarely entirely frugivorous, with insects, gums and leaves providing alternative food sources.

To explore this variation, we reviewed a comprehensive compilation of 290 primate dietary studies from 164 localities in 17 countries across the entire Neotropical realm. Sampling effort varies considerably between sites and species (Hawes et al. 2013), which we accounted for here when comparing the taxonomic richness of fruiting plants recorded in primate diets, and the relative contribution of frugivory to the overall diet. We also found strong evidence to support the long-held hypothesis that body size imposes an upper limit on insectivory and a lower limit on folivory, and therefore that frugivory is most important at intermediate body sizes.

Frugivory continuum in relation to body size, showing a peak in medium-sized primates

One of our most surprising finds was that primates with wide geographic ranges do not necessarily consume a wider diversity of fruits, perhaps because these species tend to be generalist consumers. Another surprise was that primates with higher prevalence of fruit in their diets are among the most poorly studied, meaning we still have a lot to learn about their importance as consumers and seed dispersers in tropical forests.

Image credits:

1. Saguinus oedipus: http://commons.wikimedia.org/wiki/File:Cottontop_tamarin.JPG
2. Pithecia irrorata: © Edgard Collado
3. Alouatta guariba: http://commons.wikimedia.org/wiki/File:Southern_brown_howler_monkey_female_sp_zoo_2.JPG

References:

Hawes, J.E., Calouro, A.M. & Peres, C.A. (2013). Sampling effort in neotropical primate diet studies: collective gains and underlying geographic and taxonomic biases. International Journal of Primatology. DOI: 10.1007/s10764-013-9738-0 (in press).

Who are the murderers and who are the victims in forest soils? Read about Babett Günther and co-workers’ homocide investigation in the Early View Oikos paper: “Variations in prey consumption of centipede predators in forest soils as indicated by molecular gut content analysis”. 

Here’s their story about the study:

We all know from TV series like CSI: crime and murder always happen in the dark, in remote and obscure places where the victim is overwhelmed by the sneakily attacking offenders. Killing is not only confined to humans, and the offender may have some good reason to kill, for example predation and nutrition. But what are the circumstances of successful killing and predation? Are there more killings when there are more/smaller/less defensive victims? Or is it the size of the attacker? Or is it because of the structure and topography of the crime scene?

We tested these hypotheses in one of the most obscure and unearthly environments: the soil and litter layer of different forests. The victims: springtails, dipteran larvae and earthworms. The delinquents: small and large stone centipedes of the genus Lithobius. Just like TV forensic scientists, after rummaging through the dirt, looking for DNA evidence, drinking a lot of coffee and after many long nights in the laboratory, we finally solved the case:

large centipedes are able to kill more prey at high prey abundances and in unstructured environments, while the opposite was true for small predators. Interestingly, small centipedes were also shown to overwhelm large victims, indicating high criminal energy in small creatures, as has been already demonstrated for humans (e.g. John Dillinger).

In a seminal contribution published in 1972 (Nature, 238; 413-414), Sir Robert May showed that from a mathematical point of view the more complex an ecological community is (in terms of the number of species and interactions in the system), the less stable it is. However, complex ecological communities are observed in nature, and so the issue on how species in large complex ecological communities may coexist is still a relevant and open debate in ecology.

In recent years several searched for new principles allowing ecosystems to persist despite their complexity, but a general consensus on this topic has not yet been achieved.

Last summer, an intriguing work published in Science (A. Mougi, M. Kondoh, Science 337, 349) claimed that specific mixture of antagonistic (predator-prey) and mutualistic interactions (beneficial for the interacting individuals) between species is likely to contribute to stabilize ecological communities. Furthermore, they also found that in this type of hybrid community “…increasing complexity leads to increased stability”. As mixing of interaction type is the norm rather than the exception in ecological communities, these conclusions might have led to a final word in the “complexity-stability paradox”.

In our work “Disentangling the effect of hybrid interactions and of the constant effort hypothesis on ecological community stability”, published Early View in Oikos, we show that this is not the case. Indeed, we proved that mixing of mutualistic and predator-prey interaction types does not stabilize the community dynamics and we demonstrate that a positive correlation between complexity and stability is observed only if  species interact so that generalist species (the ones with several “partners”) interact very weakly (in terms of intensity) with respect to specialist species (which have only few partners). We also show that the main findings presented in Mougi and Kondoh work arise as an artifact of the peculiar rescaling of the interaction strengths they imposed. Indeed, using their methodology, the very same effect of ecosystem stabilization may be obtained for generic random ecological networks.

In conclusion, the mismatch between theoretical results and empirical evidences on the stability of ecological community is still there also for communities with a mixing of interaction types, and the “complexity-stability” paradox is still alive. Our work suggest that complexity and stability may be reconciled if a particular scaling of the interactions strength with the species degrees (number of resources) exists, but further studies and experimental evidences are still needed to better understand the role of interaction strengths in real ecological communities.

Samir Suweis, Jacopo Grilli,  Amos Maritan

A sheep increasing 4 times in size, starting to eat competing rabbits! Wow, that would be something! And it’s almost true, at least in the ciliate world! Find out more in the new Early View paper “Trait-mediated apparent competition in an intraguild predator–prey system” by Aabir Banerji and Peter J. Morin. Here’s their short version of the paper:

This investigation stemmed from our earlier work on the inducible trophic polymorphism (ITP) of Tetrahymena vorax.  In the presence of competing ciliates, individuals of T. vorax (starting as small, pear-shaped bacterivores) can completely reconstruct their cytoskeletons and increase their size to up to four times what it was before, becoming spherical predators capable of rapidly phagocytizing their competitors. This transformation occurs within six hours and is completely reversible.  In the figure below, the red arrow points to the cytopharynx (“mouth”) of the predatory morph.

Though there are several real-life ITPs among macroscopic taxa that are roughly analogous to that of T. vorax, I find the fictional example shown below to be slightly more accurate (and fun to present).

While attempting to see which prey we could rear T. vorax on of the ones we had in-stock at our lab, we noticed that T. vorax seemed to get bigger when fed bigger prey.  This is a pattern that has been observed in various other ciliate predators (and a few macroscopic predators), as well.  I was dying to call it “chasmatectasis” (from the Greek words for “gape” and “stretching”) – a term inspired by the way one of my friends in the medical profession had described the phenomenon of competitive eating: “self-induced gastrectasis.”  (Luckily, my labmates talked me out of coining lame phrases at this point.) 

What we really wanted to know was whether this phenomenon could give rise to a novel form of apparent competition (one that was trait-mediated, rather than density-mediated).  Conceptually, this would be like what happens in the Pac-Man video game – eating large prey items allows the predator to eat things it normally would not be able to eat.

As it turns out, it can.

In subtropical and tropical forests up to 90% of woody plant species depend on fruit eating animals for the dispersal of their seeds. Birds are the most diverse and abundant animal group that acts as seed dispersers. Yet, many birds are threatened by the ongoing deforestation and the introduction of alien invasive (non-native and ecosystem-transforming) plant species. It remains a challenge for ecologists to predict how different frugivorous bird species respond to these environmental changes with ultimate consequence for the dispersal service they provide.

Fig 1 Large, undisturbed subtropical forests nowadays are generally confined to protected areas and gorges. On the plains forest extent is heavily reduced by intensive sugar cane farming.

Factors that may drive bird responses to habitat disturbance comprise different dependencies on forested habitat and fruits as resources. Whereas forests specialists only occur in large, undisturbed forests, forest generalists often prevail in smaller fragments, and forest visitors generally dwell in open habitat such as grassland. Similarly, obligate frugivores exclusively feed on fruits to meet their dietary demands, whereas partial frugivores supplement their diets with insects or floral nectar, and opportunistic frugivores only rarely pick some of their favorite fruits.

Fig 2 Forest island within sugar cane. Forest specialists and specialized frugivores are practically absent from such islands.

In our study “Guild-specific shifts in visitation rates of frugivores with habitat loss and plant invasion”, now on Early View in Oikos, we investigated whether changes in visitation rates of bird species (to plants for foraging on fruits) with forest loss and plant invasion can be predicted by their different dependencies on forested habitat and fruits as resources. To do so, we conducted extensive observations of plant-frugivore interactions in a subtropical South African forest landscape. These forests are highly diverse, and more than 700 bird species can be found in the region! However, South African forests are also under increasing pressure from intensive agriculture and urban sprawl, and many invasive plant species have replaced the natural vegetation. Fieldwork was fun but could be tough ­– sometimes we observed no visitor in 18-h of observation! Further, we wore military-style ‘ghillie suits’ for camouflage, a very effective way to hide in dense vegetation and minimize disturbance of birds. However, a woolen suit is a rather poor choice in South African summer…

Fig 3 Trumpeter hornbills (Bycanistes bucinator) are among the largest avian frugivores in South Africa. This individual feeds on fruits of Ficus glumosa.

Fig 5 Speckled mousebirds (Colius striatus) are generalized frugivores which are able to persist in a wide array of differently disturbed habitats. Unfortunately, few fruits on this Tassel-berry (Antidemsa venosum) shrub are fully ripe yet.

Still, the African bird life was totally worth it, and we found highly interesting results. As expected forest specialists were most negatively affected by habitat loss. However, interestingly, obligate frugivores were overall least affected by habitat loss and plant invasion. Fully depending on fruits requires a generalized fruit choice, which seems to make obligate frugivores more robust to changes in habitat conditions. In contrast, visitation of partial and opportunistic frugivores declined – a pattern that can be explained by the comparably more specialized or ‘picky’ foraging behavior of non-obligate frugivores. Specialist foragers were particularly rare when high degrees of habitat loss and plant invasion interacted in synergy.

Fig 4 Testing the ghillie suit in a farmhouse garden. When hiding in even denser vegetation, the observer becomes practically invisible to the avian (and human) eye.

In summary, our study shows that forest loss and plant invasion may especially negatively affect forest specialists and specialized frugivores. This is worrying, as it is those ‘unusual’ species, which by their diverging ecological and behavioral differences from generalized species, considerably contribute to the astonishing diversity of subtropical and tropical forests. Not to forget that most often, they are also wonderful to look at.

Fig 6 These fruits of invasive Bugweed (Solanum mauritianum) show clear marks of pecking frugivores. The plant flowers (background) and fruits at the same time and is able to do so year-round, a significant advantage over many native plant species.

Ingo Grass, Dana G. Berens and Nina Farwig

Congratulations, Jeff Ollerton, Rachael Winfree and Sam Tarrant for passing 100 citations for their paper “How many flowering plants are pollinated by animals?”, published in Oikos in March 2011.

But Jeff, how did you come up with the idea for the paper?

The idea for the paper arose when I was trying to find a solid figure in the literature for the proportion of plants that are biotically pollinated.  It’s an important starting point for any argument about the importance of conserving pollinators, I think: policy makers like to be able to present numbers.   Lots of figures were being quoted, from a range of sources, but once you follow the reference chain back through the papers that cite them you find that numbers which are cited as solid facts disappear into speculation and guestimates.  Like many of the simple and obvious questions, the assumption is that we “know” the answer.  That’s no basis for science-informed conservation policy, but I suspect that it happens all too frequently.

Did you know that the paper would be cited?

To be honest, yes, because a lot of studies and papers are now focussing on the ecology and conservation of plant-pollinator interactions, and our paper provides an initial rationale for why it is important to study them.  But I didn’t appreciate quite how well cited it would be, that certainly took us by surprise:  over 30 citations per year is a high rate in ecology!

Visit Jeff’s blogg:

 

We are very happy to present our cover for 2014! As you might recall, we had a photo competition to find a  nice photo showing ecology in action. And we have a winner!

Congratualtions Prof. Erik Svensson, Lund to the fantasti