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:

ResearchGate page:


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.


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.”


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).;

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.



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),


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.


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.


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.


  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.


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


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

The authors through Christophe Mensens

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:


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

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


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

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

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.


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!)


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


  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



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.


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


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

Martina Del Bello

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.


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

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

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


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


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

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


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.


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.


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.


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.


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.

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.



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


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

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

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


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

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


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


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

The authors through Thomas Püttker

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 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.

Posted by: oikosasa | September 11, 2014

Can viruses alter host behavior?

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



Oikos presentation Stafford-Banks

Posted by: oikosasa | September 9, 2014

Better being early?

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

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

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

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

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

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


Posted by: oikosasa | September 5, 2014

Pollinator decline effects on plants

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

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

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





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

Posted by: oikosasa | September 2, 2014

From rich to poor – what happens in the soil?

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

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

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




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



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


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

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


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


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

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


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

Posted by: oikosasa | August 22, 2014

Frugivory and seed dispersal

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

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

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

LaVera LaVera2

Posted by: oikosasa | August 19, 2014

How much do asexual plants actually change?

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

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

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

Asexual1 Asexual2

Posted by: oikosasa | August 15, 2014

Changing perspectives

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

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

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

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

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

Norma1 Norma2 Norma3 Norma4 Norma5

Posted by: cjlortie | August 14, 2014

New formal synthesis section for Oikos papers

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

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

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







Posted by: oikosasa | August 11, 2014

Do invasive species alter litter nitrogen release?

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

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

mixed litter (1) mixed litter2

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

Mixed litter3

Posted by: oikosasa | August 6, 2014

Non-native plant species benefit from disturbance

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

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



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

Posted by: oikosasa | July 18, 2014

Food flow across ecosystems

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

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


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

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


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


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

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


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


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

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


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


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

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

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


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

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


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


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

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

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


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

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

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


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

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


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

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

Infected Silene vulgaris at the Col du Galibier, France.

Infected Silene vulgaris at the Col du Galibier, France.

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

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

Shorter (ie, Twitter) version:

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


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









































Posted by: oikosasa | July 10, 2014

Tuna-tern facilitation

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

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


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

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

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

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

Posted by: oikosasa | June 24, 2014

How do behavioral changes affect ecosystems?

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

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

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


Wood frog tadpoles swim in a pond mesocosm.

Wood frog tadpoles swim in a pond mesocosm.


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

Brad Carlson uses a dipnet to sample a pond community.

Brad Carlson uses a dipnet to sample a pond community.

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

Brad Carlson observes tadpole behavior in mesocosms.

Brad Carlson observes tadpole behavior in mesocosms.

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

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

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


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

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

Posted by: oikosasa | June 17, 2014

Carbon flow between lakes and ground

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

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


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

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

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

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

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

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

Photo 3: Installation of the plastic curtain in Gollinsee.

Photo 3: Installation of the plastic curtain in Gollinsee.

Photo 4: Emergence trap used in our study.

Photo 4: Emergence trap used in our study.

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





Posted by: oikosasa | June 13, 2014

How does climate change affect pollination phenology?

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

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

By Jessica K.R. Forrest


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

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