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.

Eklöf1

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.

Eklöf1

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.

 

Posted by: oikosasa | February 9, 2015

Phenotypic effects of climate change

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 21st 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.

Soay

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.

Posted by: oikosasa | February 4, 2015

Synthesising: Population genetics and tropical ecology

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.

Yaoyoij

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.

Posted by: oikosasa | February 3, 2015

Invaders in plant-pollinator communities

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

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.

Posted by: oikosasa | February 2, 2015

To live longer – choose the right place to live?

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.

Monnett1

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.

Monnett2

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

 

Posted by: oikosasa | January 30, 2015

Frugivores and seed dispersal

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

barro colorado island - bat-fruit network (marco mello) 2 barro colorado island - bat-fruit network (marco mello)

Posted by: oikosasa | January 28, 2015

Herbivory response to global warming

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.

Bild1

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).

Bild2

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.

Bild3

Masahiro Nakamura and co-workers

Posted by: oikosasa | January 27, 2015

Soil, elevation and plant growth

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”. 

Abisko 1

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.

Abisko 2

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.

Abisko 3

 

Jonathan de Long and co-workers

Posted by: oikosasa | January 23, 2015

How do ants affect spider populations in coffee plants?

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 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.

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.

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.

Linda4

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

Posted by: oikosasa | January 22, 2015

January Cover

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.

OIKOS_124_01_COVER-1.indd

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.

Posted by: oikosasa | January 20, 2015

Herbivory effects of climate change

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 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.

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.

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.

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. 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

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)

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)

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.

Posted by: oikosasa | January 16, 2015

Effects of population densities on invasiveness

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).

Invading2

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.

IInvading3

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).

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

Posted by: oikosasa | January 15, 2015

Travelling around to catch more parasites?

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.

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.

Posted by: oikosasa | January 14, 2015

Stay or go for next clutch?

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.

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

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 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)

Posted by: oikosasa | January 9, 2015

Now or never: adaptive phenology and biotic interactions

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.

infryst snödroppe-2707

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”

Posted by: oikosasa | December 19, 2014

Welcome new SE: Francois Massol

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

DSC_8807What’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).

2008 janv Beauplan FM malaco-bidon

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

 

Posted by: oikosasa | December 17, 2014

How small rodents in the Arctic affect birds in New Zealand

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

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

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

 

Posted by: oikosasa | December 16, 2014

Not easy being a seedling…

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.

Photo3

A swamp wallaby discovers a eucalypt seedling.

Posted by: oikosasa | December 15, 2014

Butterfly resilience to climate warming

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 mosaic2,3. Populations that feed only on Pedicularis and populations that feed only on Collinsia differ in a suite of adaptations2,4,5. 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)

Posted by: oikosasa | December 11, 2014

New Editor: Andrew MacDougall

2013-07-06 14.23Welcome 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

Posted by: oikosasa | December 9, 2014

Editor’s Choice December

DriesThe 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

Posted by: oikosasa | December 5, 2014

Welcome Sara Magalhaes New SE

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

sara peq11.     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.

Sara3 urticae

Photo: Jacques Denoyelle

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.

 

Posted by: oikosasa | December 3, 2014

How plant genetic diversity affects herbivory

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.

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

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.

 

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.

Posted by: oikosasa | December 2, 2014

Rodents and the yummy spines

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),

Rat1

A white-throated woodrat (Neotoma albigula)

 

 

 

 

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.

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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

 

Posted by: oikosasa | November 28, 2014

How do different herbivores affect plant communities?

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.

Kim

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.

 

Posted by: oikosasa | November 26, 2014

New SE: Leif Egil Loe

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?

Loe2Most 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.

  1. 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.

Loe1

  1. 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.

  1. 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.

Posted by: oikosasa | November 26, 2014

Pesticide effect on biodiversity and ecosystem functioning

Pesticid2Global 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.

Bild1

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.

Pesticid1

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

Posted by: oikosasa | November 21, 2014

Same looks, different behavior

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

Posted by: oikosasa | November 20, 2014

Predation and transmission of direct life-cycle parasites

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:

giovanni_strona

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.

oik1850-fig-0001

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.

Posted by: oikosasa | November 18, 2014

Sexual size dimorphism in island plants

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.

Crobusta1

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-analyses1, 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.

gamfeldt photo 4

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.

gamfeldt photo 2

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!)

OLYMPUS DIGITAL CAMERA

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.

gamfeldt photo 1

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.

 

Posted by: oikosasa | November 12, 2014

Are mismatches the norm?

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

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

Posted by: oikosasa | November 11, 2014

Elevation effects on body size

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

Ovarioles from Melanoplus pellucida

 

Levy2

Melanoplus dodgei from alpine site

Melanoplus dodgei from alpine site

Posted by: oikosasa | November 7, 2014

Multifractals in intertidal biofilms

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.

Bello2

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.

Bello1

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

Posted by: oikosasa | November 4, 2014

Editor’s choice November

DriesAs 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.

Posted by: oikosasa | October 24, 2014

Everything is connected – in nature too

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.

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).

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.

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’.

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.

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

 

 

Posted by: oikosasa | October 21, 2014

Marsupial browsing effects insect damages

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).

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).

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.

Hahn1

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.

Hahn2

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.

 

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.

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.

Posted by: oikosasa | October 14, 2014

The struggle for safety: caterpillar against birds

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 20th century.

Cat1

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.

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.

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.

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.

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.

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

Posted by: oikosasa | October 10, 2014

A voyage into soil darkness

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.

beechforest

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.

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”

 

 

Posted by: oikosasa | October 7, 2014

Drought – increase or decrease herbivore abundance?

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.

 Grasshoppers1

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.

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.

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.

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

Posted by: oikosasa | October 3, 2014

What exactly can network models predict?

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.

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.

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

Posted by: oikosasa | September 30, 2014

What causes dialects in bat?

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.

Bat1

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.

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

Posted by: oikosasa | September 26, 2014

Costs of living in a nest

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]

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]

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]

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

The authors through Gustavo S Requena

Posted by: oikosasa | September 23, 2014

Towards the catastrophic collapse?

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.
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.

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

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”.
Posted by: oikosasa | September 19, 2014

Finding the food in complex environments

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.

 

Movements

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.

Beta1

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.

Beta2

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.

Beta3

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

Posted by: oikosasa | September 12, 2014

White stork modelling

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. Juni11 103 Mit_Sender

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.

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