Posted by: oikosasa | August 13, 2013

Meet our EiC in London next week!




Posted by: oikosasa | August 2, 2013

Moving plants and invasions

Climate change and plant movements and invasions was discussed during the ESA-meeting 2011. The result – a Forum paper is now published online in Oikos: “Movement, impacts and management of plant distributions in response to climate change: insights from invasions” by P. Caplat et al. Below you find Yvonne Buckley’s background story to the paper:

Plants are moving as their habitat changes due to climate change. If species are to persist they are required to adapt or move somewhere else. Species dynamics are extremely hard to predict, making global change research a challenging enterprise. Invasion ecology however has many case-studies, concepts and challenges in documenting, predicting and managing how species move, and how their movement affects ecosystems.

Invasive plants are extremely good at moving and present very real challenges for predicting where they will move to, how fast and how ecosystems will respond to immigrants. We invited 10 colleagues from around the world with diverse interests in the ecological, evolutionary and social dimensions of invasion to discuss how invasion ecology can contribute to predictions of plant movement in response to climate change at a special session of the 2011 Ecological Society of America meeting in Austin. Sparked by presentations and discussion at that session we wrote a discussion piece for the Oikos Forum.

Climate change and biological invasions exhibit similar dynamics and processes. In the following figure, we show A: a New-Zealand native tree (Nothofagus menziesii), recruiting above the climatic tree line in the Mataketake Range, New-Zealand (courtesy of M. Harsch); B: an invasive pine (Pinus nigra) expanding on a mountainous grassland near Lake Coleridge, New-Zealand.


In the paper, we outline the similarities between invasion dynamics and climate induced range-shifts. The figure below shows how concepts from invasion biology can contribute to questions relevant to climate change research.


Many of these concepts concern the properties plants should have to be able to track their environment or adapt to new conditions. The colonisation of new environments emphasizes the role of dispersal, which has been intensely studied in invasion biology. The following picture illustrates this. A: Invasive thistle Carduus nutans responded to experimental warming by growing taller, therefore increasing its dispersal ability; B: having light, winged seeds allows pine tree Pinus nigra to spread far and fast; C: the dispersal traits of invasive Crepis sancta evolved rapidly when the plants colonized a fragmented urban environment (courtesy of G. Przetak); D: high seed production , amongst other traits, allow Acacia pycnantha to invade grasslands in the Western Cape, South Africa.


Invasion processes are not entirely analogous with plant movements in response to climate change but they do present some useful examples and a large volume of data which could be synthesised to shed light on ecological, evolutionary and social processes that are involved when plants move.

Posted by: oikosasa | July 29, 2013

Swans go with the flow

Many animal species show seasonal switches in their habitat use. For example, animals may move between aquatic and terrestrial habitats, flowing and still waters, coastal areas and open seas, or forest floors and canopies. How do animals decide which habitat to use? One way to understand animal habitat selection is to focus on the energetic gains and costs associated with foraging in each habitat. This has been the basis of much ‘optimal foraging’ research over the past few decades. Foraging models, which calculate the net energy intake per unit time (‘profitability’) available to the animal while foraging in different habitats, can yield a process-based understanding of why animals switch habitats.

In our paper Go with the flow: water velocity regulates herbivore foraging decisions in river catchments , now published Eary View, we used a combination of observational, experimental and modelling work to understand why flocks of non-breeding mute swans (Cygnus olor) show a seasonal switch in habitat use in shallow river catchments. From our previous work, we knew that swans switch from feeding on grasses in pasture grass fields, to feeding on aquatic plants in the river itself, between April and May each year. Due to their high food requirement (up to 4 kg of fresh vegetation per day), lack of predators and high tolerance to disturbance, non-breeding swans are ideal for studies of the influence of foraging profitability on habitat selection. Hence we suspected that the habitat shift would be linked to seasonal changes in one or more of three parameters: food quantity, food quality, and metabolic foraging cost.


A flock of mute swans feeding on submerged plants in a shallow rive

A flock of mute swans feeding on submerged plants in a shallow rive


We combined field and literature data with an optimal foraging model to investigate the observed seasonal habitat shift by mute swans. Our study system for this investigation was the River Frome in southern England, which has a population of approximately 300 swans. We measured the quantity and quality of the two food resources available to swans, aquatic plants and pasture grass. We took quantitative plant samples each month from 18 paired river and field sites within the catchment to measure how the biomass of each food resource changed over the study period. The energy content of plant and swan faeces samples from four of these sites were determined using bomb calorimetry, which showed that the food quality was relatively constant over the study period. We estimated the intake rates for aquatic plants by conducting feeding experiments on captive swans, and for pasture grass by allometric scaling of published data. We used published literature and calculated water velocities to estimate foraging costs. Whilst foraging costs of pasture grass feeding were stable over time, river feeding became more efficient as water velocities declined between spring and summer; slower water meant less energy had to be expended swimming.


The lead author with a tray of swan faeces for energy analysis, illustrating the less glamorous side of working with large, charismatic vertebrates

The lead author with a tray of swan faeces for energy analysis, illustrating the less glamorous side of working with large, charismatic vertebrates


The lead author delivers part of the ad libitum supply of aquatic plants to a captive swan at the start of the functional response experiments

The lead author delivers part of the ad libitum supply of aquatic plants to a captive swan at the start of the functional response experiments


Finally, we used an optimal foraging model to predict the average net rate of energy gain in each habitat, for each month between March and September. The model could have either fixed values (i.e. average values for the study period) or variable values (i.e. monthly values) for the key parameters, to allow us to assess the effects of seasonal changes on profitability and habitat use. We compared the predicted ‘best’ habitat for each month with the observed field data on habitat use. By sequentially testing alternative models with fixed or variable values for food quantity, food quality and foraging cost, we found that we needed to include seasonal variance in foraging costs in the model to accurately predict the observed habitat switch date (i.e. April to May). However, we did not need to include seasonal variance in food quantity and food quality, as accurate predictions could be obtained with fixed values for these two parameters. Therefore, our model indicated that the seasonal decrease in aquatic foraging costs was the key factor influencing the decision to switch from pasture to river feeding habitats. Many previous studies have ignored the role of seasonal changes in foraging costs in driving switches between habitats. Our study offers a mechanistic understanding, based on the gains and costs associated with different food resources, of the observed shifts of a generalist herbivore between alternative habitats.

Understanding the factors which determine habitat selection are necessary to explain the patterns of animal distributions that we observe in nature. Furthermore, we aim to use our understanding of swan habitat selection to inform ecosystem management. Where they feed in shallow rivers, flocks of mute swans may damage the plant community and threaten conservation objectives. Herbivore damage to valuable plant communities is a problem seen around the world, for example deer in temperate woodlands and geese in agricultural crops. Where we understand the factors which determine herbivore habitat use, we may be able to manipulate these factors to shift herbivores away from the threatened habitat. Whether or not we can successfully use our understanding of the rules of habitat selection to devise practical habitat management schemes to prevent overgrazing, it certainly provides an interesting applied focus for future research in this area of ecology.

Kevin A. Wood

Posted by: oikosasa | July 26, 2013

Personality and metabolic rate

Do bold individuals have higher metabolic rates? Find out in the new Early View paper “Personality and basal metabolic rate in a wild bird population” by Sandra Bouwhuis and co-workers. Here’s Sandra’s short summary of the study:

Like humans, individuals of many species are found to vary in their personality type. Some individuals are bold and eager to explore new environments, while other individuals are shy and more cautious. Such personality variation has been suggested to be related to general lifestyle differences between individuals, such that bold individuals opt for a ‘live fast, die young ‘ lifestyle, while shy individuals invest in survival and the future. On the physiological level, such individual differences have been proposed to be supported by different metabolic machinery and, as a result, different metabolic rates. This latter theory was tested in a wild population of great tits, living in Wytham Woods in the UK, over three years. Contrary to the expectation, among 700 individual birds no strong relationship between metabolic rate and personality was found. Instead, the results of the study suggest that individual metabolic strategies may be highly variable and that such metabolic strategies, instead of an average metabolic rate, may be related to personality variation.

Wytham Woods mistnetted great tit personality assay room

Posted by: oikosasa | July 22, 2013

Mom knows best – maternal care in perennial plants

How can we provide the best circumstances for our kids? The new Oikos Early View paper “Adaptive transgenerational plasticity in the perennial Plantago lanceolata” , by Vit Latzel and co-workers, deals with this issue – in plants. Read Vit’s story here:

Imagine that you have to live your whole long life in one spot and that your kids, for whom you cannot even choose the father, will then live very close to you without the possibility of them finding a better environment. How can you best provide for them and make their lives at least slightly easier? This is exactly the challenge that many cross-pollinated long-lived plants must face. Luckily for some mothers, it seems that they can prepare offspring for the environment that they will be facing – giving them an advantage over unprepared competitors. They could do this through the mechanism known as adaptive maternal effects or adaptive transgenerational plasticity. However, rigorous demonstrations of this have been surprisingly rare, probably because appropriate experiments are difficult to conduct and/or the wrong traits have been measured. We did a straightforward experiment on the common perennial Plantago lanceolata (ribwort plantain), testing whether offspring grown in the same level of nutrient availability as their mothers were more successful than offspring grown in a non-maternal environment. Unlike other studies, we considered total carbon storage in roots as the measure of offspring success, because, in contrast to fitness estimates based on single-year fecundity, storage amounts accurately indicate long-term success of polycarpic perennials across several seasons. We found that offspring took an advantage of maternal environmental nutrient levels where they accumulated significantly more carbohydrates than those grown in non-maternal environments. This adaptive transgenerational plasticity was consistent across maternal genotypes and was not affected by climatic fluctuations during offspring development. Our work suggests that adaptive transgenerational plasticity is common in Plantago lanceolata. We also believe that if appropriate estimates of plants success are considered, similar transgenerational adaptive plasticity can likely be found in many other perennial species, and that transgenerational modification of storage dynamics in perennial plants can contribute to their ecological variation.

Ribwort plantain in a natural population and in our cultivation. Graph shows the higher level of carbon storage in offspring grown in maternal than in non-maternal nutrient environment.

Ribwort plantain in a natural population and in our cultivation. Graph shows the higher level of carbon storage in offspring grown in maternal than in non-maternal nutrient environment.

Posted by: oikosasa | July 19, 2013

Scared of darkness?

Are you scared of the dark? Predators can change the species present in a community by consuming particular individuals removing them from the ecosystem. However, a new paper published Early View in Oikos “Fear in the dark? Community-level effects of non-lethal predators change with light regime”, Coreen Forbes and Edd Hammill” shows that under dark conditions, fear of predation alone is enough to lose species from communities. Under dark conditions, photosynthesis is impossible meaning the only species that can survive are ones that can collect energy from existing sources. Moving around to collect this energy also increases the chances of encountering a predator, so when scared, some species reduce the rate at which they move around. This reduction in movement means other species can harvest the energy source faster than the “scared” species. Because the scared species is now less competitive, it can be driven to extinction despite the fact it is not being eaten by predators. Our research shows how important predators are for keeping ecological communities in order


Posted by: oikosasa | July 16, 2013

Welcome Isabel Smallegange – new SE

OLYMPUS DIGITAL CAMERAWelcome to the Oikos Editorial Board, Dr. Isabel Smallegange, University of Oxford, UK. Isabel’s research focuses on unravelling the mechanisms that maintain male polymorphisms, and on understanding and predicting the eco-evolutionary consequences of (human induced) environmental change. In her studies she uses mites as a model system and combines modelling with behavioural and population experiments. More info is found on her website:‎.

Isabel, what’s you main research focus at the moment? 
The focus of my research is to understand how ecology and evolution interact to determine the evolution of traits and the dynamics of populations in response to environmental change. I specifically focus on the evolution of male dimorphism and combine theory with experiments to unravel the links between ecology and evolution.

Can you describe you research career? 
I started out in behavioural ecology as I was (and still am) fascinated by all the different behaviours that animals display. During my PhD at the Netherlands Institute for Sea Research I studied the foraging behaviour of shore crabs. However, by the end of my PhD I wanted to scale up my work to the population level, which was not possible with shore crabs, and therefore I went to the Max Planck Institute for Ornithology to analyse long-term datasets on bird abundances. This first Post Doc was a great learning experience, however, I missed the experimental element to my research and moved to Imperial College London where I set up a laboratory to use mites as a model system to study population dynamics and the evolution of male dimorphism. My lab has now moved to the University of Oxford where I’m continuing my research on eco-evolutionary dynamics.

male morphs mites more mites copy

How come that you became a scientist in ecology? 
I always liked biology and from a young age I was fascinated with animal behaviour. I actually thought I would never be able to get a job in behavioural ecology but, luckily, I did find a PhD position to study animal behaviour. During my PhD I learnt many different skills that set me up for a career in ecology. Although now I’m not studying animal behaviour anymore, I still work with animals on very exciting questions in ecology and evolution.

What do you do when you’re not working? 
At the moment I spend most of my spare time with my 6-month old son who demands a lot of attention!

Selected publication: Smallegange IM, Coulson T. 2013. Towards a general, population-level understanding of eco-evolutionary change. Trends in Ecology and Evolution 28:143-148.

The introduction of non-native plants usually invokes a wave of pessimism among biologists.  Some of these introduced plants can invade natural ecosystems where they can cause tremendous problems.  And to make matters worse, it is very difficult to predict much about the ecological impact of a particular non-native plant prior to its introduction.  We argue that one important consequence of a plant introduction is fairly predictable:  which native herbivores are able to colonize it.

In the Early View Oikos paper “Predicting novel herbivore-plant interactions”, Ian Pearse, David Harris, Richard Karban, and Andrew Sih argue that we can predict which native herbivores will successfully colonize which introduced plants if we understand some of the mechanisms of native herbivore plant interactions and the general properties of native food webs.

The basis for predicting novel associations between herbivores and plants is to define the “match” between an herbivore and its potential hosts.  The logic behind this ends up being analogous to the way the Netflix movie website guessed (perhaps correctly) that I might like to watch “His Girl Friday” next (it is similar to another movie that I watched recently) or maybe an episode of “Downton Abbey” (a show that seems to be popular with many people right now).  Indeed, the attempts to “match” us with a novel product (log in to Amazon) or person (visit are essentially pervasive to anyone who ventures onto the internet.  This works because internet sites and companies collect a large (creepy?) amount of information about us and the products they sell.

Microsoft PowerPoint - hostmatchdotcom.ppt

In the context of novel herbivore-plant associations, we already know many of the factors that drive these associations (phylogenetic constraint in host breadth, secondary metabolites, phenology, etc).  And we have even begun to compile information about many native plant-herbivore food webs, which is perhaps akin to Netflix’s list of movies that I and other costumers have watched.  So, this paper suggests that (when armed with accurate native food webs and good lists of plant traits and evolutionary histories) we can start to make more accurate predictions about which native herbivores will colonize which non-native plants.

Of course, the natural history of individual organisms is complicated, and some interactions will be hard to predict.  For example, the interaction between an herbivore and its novel host is an evolving relationship (see a recent Oikos review by Matt Forister dealing with this topic).  But for many cases, herbivore interactions may be one of the most predictable elements of plant introductions.

Posted by: oikosasa | July 9, 2013

Editor’s Choice July

The Editor’s choice papers in the July issue of Oikos are “A critical analysis of the ubiquity of linear local–regional richness relationships” by Goncalves-Souza et al. and “Bottom–up and top–down forces structuring consumer communities in an experimental grassland” by Rzanny et al.  Both are available free online! Here’s the EiC’s motivation for the choice:

DriesBesides promoting synthesis, Oikos has a tradition in publishing studies that challenge widely accepted ecological paradigms. The ubiquity of linear relationship between local and regional species richness is such an idea that found its way to many textbooks. The potential impact of regional and local processes on community structure has been traditionally tested by regressing local against regional species richness. This approach was justified by the idea that communities controlled by regional processes are unsaturated, while those affected by local processes are not. However, while such a linear relationship has been theoretically criticized, a critical reevaluation has so far not been done. Thiago Gonçalves-Souza and colleagues reanalysed published studies with a new unbiased method and found no prevalence of linear relationships and more than 40% of misclassifications. Its apparent ubiquity appeared to be due to the use of biased statistical methods (linear regressions to detect linearity). The study demonstrated such local-regional diversity relationships to follow other ‘rules’ than linear ones. The metacommunity perspective provides a framework to study the importance of processes acting and interacting at different spatial scales. A full understanding of these mechanisms will ultimately generate synthesis on the form and strength of the local-regional diversity scaling rules.

While this framework likely advances our understanding of the processes leading to species diversity, we still lack proper insights on the relative strength of different local mechanisms (food web interactions for instance) that structure species communities. Species at intermediate trophic levels (consumers) are expected to be affected by the interplay between bottom-up and top-down effects, but synthesis on the relative importance of these effects is lacking. By analysing data from a long-term grassland diversity experiment, Michael Rzanny and colleagues demonstrate bottom–up forces to account for the major part of the explainable variation within the composition of all functional groups of consumers (plant chewers, suckers , saprophages) but also predators and parasitoids. Legumes appeared to be an especially important driver of consumer community structure. Predator-mediated top–down forces also influenced the majority of consumer functional groups, but were much weaker. In order to partition the different sources of variation, redundancy analysis was applied. Equally interesting, and again emphasising the interactive effects between local and regional processes, was the importance of different spatial components for explaining, especially, predator community structure.

The Nordic Society has put together a special symposium for the upcoming Intecol meeting.  We hope to see you all there and that you will find it an interesting set of talks.  It is a double session on Tuesday August 20th in the morning. The full programme details will be available by the end of July apparently.

Goals of the diversity symposium

The primary objective of this symposium to highlight the breadth of diversity studies, both empirical and theoretical, with an eye to promoting novelty and identifying research gaps for the next 100 years.  Ancillary goals that will be addressed to meet this overarching objective include the following.

(i) To critically examine scale as it relates to understanding ecological and evolutionary processes that shape patterns of diversity.

(ii) To develop a clear set of directions for future studies of diversity that augment species diversity estimates with genetics in spatial landscapes.

(iii) To describe pivotal concepts and relationships that limit our capacity to effectively use and measure diversity and how it has changed and will change in the future and propose solutions.

(iv) To identify the critical species and places that anchor diversity studies and enhance diversity in changing climate.

The line-up of speakers is very extensive, and the second column in each table lists the allotted time.  We designed the first session to cover mover ground quickly and directly and the second session provides a bit more time for their respective topics.

Session 1 chaired by Jens-Christian Svenning

Dr Richard Michalet The contribution of local-scale facilitative interactions to community diversity and composition


Dr Carlos Melian Connecting diversification and biodiversity dynamics across spatial scales


Mr Tadashi Fukami Spatial scale and the historical contingency in community assembly as a source of beta diversity


Dr Brody Sandel Patterns of diversity across scales: Challenges and opportunities


Dr Hanna Tuomisto A critical look at the diversity of diversity: do we know what we are talking about?


Dr Pedro Peres-Neto Spatial autocorrelation, metacommunities, and null models: the thrills of diversity


Dr Franz Uiblein Widely distributed species versus species complexes in the oceans: where to go towards management of species-rich resources and habitats?


Summary by Chair


Session 2 chaired Christopher Lortie 

Dr W. Daniel Kissling Multi-species interactions across trophic levels at macroscales: retrospective and future directions


Mr Matthias Schleuning Integrating functional and interaction diversity into biodiversity-ecosystem function research


Dr Lonnie Aarssen Evolution and the sizes and numbers of species:  unpacking the diversity of vegetation


Dr Christian Schöb Global patterns of β-diversity along alpine gradients point to locally changing drivers of community assembly – but only in the absence of foundation species


Dr Christopher Lortie Diversity versus interactions: are diverse groups more important than large effects?



Posted by: chrislortie | July 3, 2013

Fun ecological synthesis facts

In my recent explorations into synthesis and the role of Oikos and other major drivers of this movement, here are some facts from Web of Knowledge and online search tools.

(1) Close to 20,000 primary research publications discuss/report effect size estimates in ecology.

(2) Approximately 15 times more meta-analyses published in ecological journals relative to systematic reviews.

(3) PLOSONE publishes majority of systematic reviews for most disciplines possibly including evolutionary biology.

(4) Historical signal of narrative reviews persists in modern synthesis.

(5) Citations per item to meta-analyses now trump narrative reviews.

(6) Oikos ranks 5th in publishing meta-analyses.

(7) The benefit to effort for systematic reviews generally higher than meta-analyses*.

*However, see pre-print on this as it does not necessarily mean we should do them instead of meta-analyses as evidence-based transformations are more likely to occur from meta-analyses.

frequency finalcites final

oikos meta-performancebenefit-effort plot

Posted by: chrislortie | July 3, 2013

Synthesis in ecology

I am experimenting with PeerJ as a new model to get friendly peer-review in advance of submitting to a journal.  Two papers were on my plate – a general synthesis and role of meta-analyses and systematic reviews paper and a more practical paper on how to interpret them. Any feedback appreciated!

Formalized synthesis opportunities for ecology: systematic reviews and meta-analyses. 

Practical interpretation of ecological meta-analyses.

synthesis solar system.003

Posted by: oikosasa | July 3, 2013

How does increased temperature affect herbivory?

Now online: “Increased temperature alters feeding behavior of a generalist herbivore” by Nathan P. Lemoine and co-workers. Read more about how an  increased temperature may affect plant growth and herbivory:

Temperature plays a crucial role in determining ecological processes. For example, temperature can control rates of predation, herbivory, individual growth rates, population growth rates, and mortality rates, to name a few. Unfortunately, we know little regarding the effects of temperature on herbivore choices. That is, we do not fully understand how temperature influences which foods herbivores choose to eat or which foods provide optimal diets. Herbivore physiology is strongly controlled by environmental temperature (if the herbivore is an ectotherm), as rising temperatures promote growth (to a point) and increase the demand for vital nutrients, like sugars, proteins, nitrogen, or phosphorus. If true, then daily, seasonal, decadal, or climatic fluctuations in temperature should alter the plants that herbivores consume.

We tested the hypothesis that temperature alters herbivore performance (consumption and growth rates) and feeding preferences among plant species using the Japanese beetle, Popillia japonica.


We found that the effects of temperature on P. japonica growth and consumption rates varied widely among plants species: increased temperatures stimulated growth on some plants and decreased growth on others. The differences in growth among plant species are attributable to plant nutritional quality. At low temperatures, plant nutritional content did not affect beetle growth. At high temperatures, beetles grew best on plants with high nitrogen and carbon content, perhaps reflecting increased demand for nitrogen-rich materials or carbohydrates.

Additionally, by extracting plant secondary chemicals, we found that temperature reorganizes beetle feeding preferences by altering the effects of plant chemical defenses. Interestingly, the plants that beetles preferred at high temperatures were not the plants on which beetles grew best, indicating that the beetles were making decisions that may not lead to optimal growth rates.


Our results indicate that direct effects of temperature on herbivore physiology can possibly re-organize the intensity of herbivory among plant species and that these changes can be predicted based on plant nutritional quality. These changes will become more important in the future as the climate warms.

Posted by: oikosasa | June 28, 2013

Exploitation-interference link

How interference competition affect population dynamics is explored in the new Early View paper in Oikos “Linked exploitation and interference competition drives the variable behavior of a classic predator–prey system” by John P. DeLong and David Vasseur. Here’s John’s background story and summary:

We had a hunch. While trying to understand how interference competition works, we began to suspect that traits that influenced the rate at which consumers encountered their resources would also influence the rate at which consumers encountered each other. Maybe some measure of exploitation competition would therefore be related to a measure of interference competition.

Figure 1. Traits that influence the rate of consumer-resource encounters might also influence the rate of consumer-consumer encounters, generating a link between exploitation and interference competition.

Figure 1. Traits that influence the rate of consumer-resource encounters might also influence the rate of consumer-consumer encounters, generating a link between exploitation and interference competition.


To find out, we measured foraging rates in the classic Didinium nasutum – Paramecium aurelia predator-prey system. By measuring foraging rates at different levels of both the predator and the prey, we could fit a functional response to the data and retrieve estimates of parameters that reflect the magnitude of these forms of competition. If there was any variation in those parameters, we would expect it to be correlated.


Figure 2. Here a Didinium nasutum is consuming a Paramecium bursaria.

We created 16 different populations and nudged them in different directions – they received varying amounts of nutrients, varying amounts of prey and predators, and were allowed to grow for different amounts of time. Then we pulled individuals from the populations and conducted the foraging experiments, once for each population separately. Our functional response included the power-law form of interference – mutual interference – and the standard ‘a’ parameter that characterizes exploitation. Across the populations, exploitation was strongly correlated with interference.

Figure 3. Interference competition (which gets more intense as it gets more negative) is strongly and positively related to exploitation competition (a).

Figure 3. Interference competition (which gets more intense as it gets more negative) is strongly and positively related to exploitation competition (a).


Turns out we weren’t the first ones to suspect this. In 1954, Park suggested that the two forms of competition might be linked, but since that time research into competition has largely investigated interference separately from exploitation. Keeping them separate is likely to obscure how competition influences ecological and evolutionary dynamics, especially given that interference can have a rather strong impact on foraging rates.

For example, the Didinium – Paramecium is famous for having highly variable dynamics. Usually, dropping a few Didinium into a plate full of Paramecium leads to one cycle of growth followed rapidly by the extinction of both populations. However, slowing everything down can lead to more oscillatory behavior. These variable dynamics are easily explained by the link between exploitation and interference, with low interference and low exploitation leading to oscillatory dynamics, intermediate competition values leading to stabilized dynamics, and higher values of both leading to deterministic extinction.

Figure 4. Predator-prey dynamics, here simulated for Didinium – Paramecium, vary from oscillatory to deterministic extinction due to the correlated nature of the interference and exploitation parameters.

Figure 4. Predator-prey dynamics, here simulated for Didinium – Paramecium, vary from oscillatory to deterministic extinction due to the correlated nature of the interference and exploitation parameters.


We also found a way to modify the mathematical formulation for the ‘a’ parameter that generates the kind of exploitation-interference relationship we observed. This model suggests that the rate of travel of the predator is an important driver of both forms of competition, bringing a measurable trait to bear on this problem.

Posted by: oikosasa | June 25, 2013

Welcome Michael Scherer-Lorenzen – new SE!

Michael Scherer-Lorenzen has just joined the Editorial Board of Oikos. Get to know him by reading the presentation below. And welcome to Oikos, Michael!

Scherer-Lorenzen_webIn my research I aim to mechanistically understand the biotic control of ecological processes and how global change drivers – such as climate change, land use change, nitrogen deposition, or invasive species – are interacting with this control.  Within this field I focus on the functional role of biodiversity for productivity and biogeochemical cycles. I am currently coordinating the EU Framework Programme VII project FunDivEUROPE, which aims to quantify the role of forest biodiversity for ecosystem functioning and the delivery of goods and services in major European forest types.


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

Does it matter to the way how ecosystems function whether there are only few or many species present? And if so, which are the mechanisms behind such biodiversity effects on ecosystem processes? Do such functional effects of biodiversity change with changing land use intensity or climate?
These kind of questions are at the basis of my group´s current field of research. We are focusing on processes such as productivity or nutrient cycling, with litter decomposition and plant nutrient uptake being key functions. One challenge we are currently dealing with is the quantification of resource use complementarity, which is one main mechanism that could explain positive plant diversity effects on productivity. In terms of study systems, we work in grasslands and forest ecosystems mainly, using both experimental and comparative appraoches.


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

Because there was a strong focus on ecology at the University of Bayreuth, Germany, I went to this little city in northern Bavaria in autumn 1988, to study Biology. I finished my studies with a thesis on land use effects on plant communities in Southern Chile.
In 1995, I begun my PhD within the pan-European BIODEPTH project under the supervision of Detlef Schulze. BIODEPTH was the first biodiversity – ecosystem functioning experiment in Europe at that time and was coordinated by John Lawton. The whole consortium was a real dream-team, and I learned a lot.
After finishing the PhD in 1999, I worked as an assistant to Detlef Schulze in the German Advisory Council on Global Change (“WBGU”), followed by a position as Executive Director of the Institute of Biodiversity Network (ibn). These two jobs offered interesting insights into policy advising and the function of important international treaties, such as the UN Convention on Biological Diversity, CBD.
I went back to science in 2001 as a research scientist at the Max-Planck-Institute for Biogeochemistry in Jena, Germany, where I established a large tree diversity experiment (BIOTREE).
From 2003 to 2009 I was working in the research group of Nina Buchmann at ETH Zurich, Switzerland. Here, I started to use isotopic tracers to quantify resource use complementarity and to study drought effects on alpine grasslands.
Finally, in April 2009, I got the position as a Professor for Geobotany at the University of Freiburg, which enabled me to set up my own research group on functional biodiversity research.OLYMPUS DIGITAL CAMERA

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

It all begun during field trips with my parents (my father collected beetles), where my fascination for nature was born. In school, I participated in nature conservation actions and research competitions. For example, together with friends, I was mapping amphibians or developped a protection programme for social wasps. So, it was very clear for me that I wanted to study biology after school. And so I went to Bayreuth…see above.


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

We have two wonderful children, Falk and Alva, who take most of my non-working time, of course. We are often going out into the forest just behind our garden, or take the bicycle, or play football.

Selected publication:
Scherer-Lorenzen, M. (2013). The functional role of biodiversity in the context of global change. In: D. Burslem, D. Coomes, & W. Simonson (Eds.), Forests and Global Change. Cambridge: Cambridge University Press. In press.

Posted by: oikosasa | June 18, 2013

Fish eye view of forest canopies

 “In discussing the peculiar type of refraction which occurs when light from the sky enters the surface of still water, it seems of interest to ascertain how the external world appears to the fish.” With these words renowned physicist R.W. Wood, Professor of Experimental Physics at Johns Hopkins University and proud owner of one of the firsthome aquariums, started his 1906 article “Fish-Eye Views and Vision Underwater“. The article was set to offer a scientifically based description of how a fish might view the world outside his glass tank.

Fish eye 1Even with all his intellectual curiosity and intuitiveness, Prof. Wood probably could not have imagined that decades later a modern descendant of the water camera he had once designed would be balanced on tripods in forests around the world. Nor could he have envisioned that it would soon become the standard field instrument for characterization of canopy structure and light regimes of forest ecosystems.

But let’s take a step back to understand how the fish got to view the forest.

The phenomenon Prof. Wood exploited in his experiment is governed by Snell’s law. Dating back to the 17th century, Snell’s law also known as Snell’s window is a phenomenon by which an observer looking up from beneath the water sees a perfectly circular image of the entire above-water hemisphere—from horizon to horizon. This is caused by refraction, light bending as it travels from one medium (air) to another (water). As argued by Prof. Wood, the cone of light entering the fish’s eye has an aperture of about 96°, but the rays within it came originally from a cone of 180°. This is the same phenomenon by which a fisheye lens (or hemispherical lens) is able to reach far to the sides of a scene and pull in the visual information of the entire hemisphere onto a plane.

The first practicable methods of hemispherical photographs were developed in 1924 shortly after Dr. R. Hill developed the first fisheye camera for cloud survey records and formation studies. During mid the 50s two ecologists, G.C. Evans and D.E. Coombe from the Botany School of the University of Cambridge, learned that one of these ingenious fisheye cameras had survived the war. Shortly after, they were standing under the dense shade of a small tree of Napoleona vogelii situated in Oil Palm bush near Ibadan, Nigeria. Of course – taking hemispherical photographs.

In 2007 another camera equipped with a fisheye lens was pointing upward to the sky in the canopy of yet another tropical forest, this time in Taita Hills South-East Kenya, where Alemu Gonsamo and colleagues from the University of Helsinki were conducting an extensive measurement campaign for the remnant cloud forest fragments.  Gonsamo and colleagues did not have to face many of the technological shortcomings Evans and Coombe were confronted with just half a century earlier. At that time hemispherical photograph analysis required tedious manual overlaying of sky quadrants and superimposing the track of the sun. With the advent of personal computers and with the replacement of film cameras by digital cameras, researchers are now able to develop digital analysis techniques (link here) and today various commercial and non-commercial software programs have become available for rapid hemispherical photograph processing and analysis. Yet many fundamental issues remain to be resolved.

The resulting hemispherical photographs serve as a permanent record of the canopy geometry, which can be precisely used to characterize canopy structure and light regimes. Canopy structural parameters are critical to adequately represent vegetated ecosystems for purposes ranging from primary productivity, climate change studies, water and carbon exchanges, and radiation extinction. However, as observed by Gonsamo and co-authors, standardization in the definitions of the fractional canopy cover and openness parameters has fallen short, leading to confusion of terms and concepts even in standard text books, making the comparison of historic measures futile.

Fish eye2

In the Oikos Early View paper Measuring fractional forest canopy element cover and openness–definitions and methodologies revisited Alemu Gonsamo and colleagues take an exciting tour, reviewing concepts, polishing up definitions, and presenting new methodologies to obtain large scale fractional canopy element cover and openness measures using photographs with a fisheye view perspective. Finally, in their Oikos paper, Gonsamo and colleagues argue that hemispherical photography is less time, labour and resource intensive, as compared to the traditional point based measuring techniques of canopy element cover and openness. This included measurements in topographically complex terrains.

Posted by: oikosasa | June 14, 2013

Editor’s Choice June


Oikos’ Editor-in-Chief, Prof. Dries Bonte, explains his choice of EC-papers for the June issue:

Editor’s choice papers from the June issue create synthesis on invasions.

Zenni & Nuñez  focus in a forum paper “The elephant in the room: the role of failed invasions in understanding invasion biology” on the importance of failed invasions to understand mechanisms behind invasions. They provide a review on studies documenting success and especially failures of invasions and found –not surprisingly I have to say- that only few studies have documented conclusively why populations fail to invade. The authors followed a paired approach contrasting environmental factors in invasive versus non-invasive populations of different species. They were, despite the lack of a well-developed research framework, able to demonstrate that different mechanisms may be causing failures vs. successes: propagule pressure, abiotic resistance, biotic resistance, genetic constraints and mutualist release. Rafael and Martin discuss the evidence available for the factors associated with these failures to invade. They additionally identify research field that are likely to produce misleading insights when neglecting these mechanisms of failure. Such biased reporting may thus not only mislead researchers, but certainly managers on the mechanisms leading to invasions.

There is consensus that when introduced organisms invade, they may cause considerable changes in community and ecosystem dynamics. While invasions are generally associated with negative impacts, Paul Gribben and colleagues demonstrate in their paper “Positive versus negative effects of an invasive ecosystem engineer on different components of a marine ecosystem” that an invasive engineer species may also contribute positively to marine community structure. They more specifically studied the impact of the invasive green alga Caulerpa taxifolia in southeastern Australia on the composition and abundance of the epifaunal and infauna community. More detailed species responses where experimentally approached. While contrasting impacts on different community components were obvious, they also showed that community change following the invasive species’ removal appeared strongly density dependent with the degree of recovery five months post removal related to the initial biomass. Areas with different biomasses of habitat-forming (invasive) species may subsequently have different temporal recovery trajectories. So, as highlighted by Zenni & Nuñez, the impact of the invasive species is strongly context-dependent and its impact differs according to the community components under study.

Posted by: oikosasa | June 12, 2013

Welcome Anna-Liisa Laine – new SE

We’re very happy to welcome Anna-Liisa Laine, University of Helsinki, Finland, to our Editorial Board!

Anna-LiisaRead more about her below and visit her website

What’s you main research focus at the moment?
Much of my research is focused on understanding why pathogens occur where they do. To get at this seemingly simple question I combine
experimental and molecular studies of host-pathogen co-evolution with data on epidemiology. I’m especially interested in how variation is generated in host resistance and pathogen infectivity, and how this variation affects epidemiological dynamics. While I mainly study within season disease transmission, I’m also extremely interested in how parasites transmit from one season to the next.
At heart I’m an ecologist and we do our field work in the Åland archipelago where 4000 meadows are annually surveyed for fungal pathogens of plants.

Can you describe you research career?
After completing my Masters at the University of Oulu in 2001, I started a PhD in the Metapopulation Research group at the University of
Helsinki, under the supervision of Ilkka Hanski. In my PhD I focused on understanding how host-parasite coevolution proceeds in a situation where the hostpopulations are highly fragmented. I defended my theses in 2005 and in 2006-07 in did a post doctoral project in the lab of John Thompson at the University of California, Santa Cruz. There we focused on understanding how plant-pollinator mutualism responds to changes in the local Community composition. I had another post doctoral stint in 2009-10 in with Pete Thrall and Jeremy Burdon at CSIRO, Canberra, Australia. There I had the opportunity to work with the classic wild flax-rust pathogen interaction,
addressing questions of host-parasite coevolution. Now I’m back at the University of Helsinki where I started my own lab in in 2010, and I
work as an Academy research fellow.

How come that you became a scientist in ecology?
When I was a high school student, I loved cell biology, and coming from a family of scientist going into seemed like an obvious choice.  However, when I started my studies at the university, I became fascinated with ecology. This was mainly due to two professors in those early years, Lauri Oksanen and Juha Tuomi. I had the chance to work as a research assistant in Lauri’s herbivory project and my interest for species interactions has continued ever since.

What do you do when you’re not working?
With two small kids, I’ve spent a fair amount of time playing with legos and finger painting recently… When I have a chance, I go

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Posted by: oikosasa | June 4, 2013

How ants and plants interact over space in the Amazon?

I protect you and you feed me, says the ant to the plant…read more about ecological networks in the new Early View paper “Spatial structure of ant–plant mutualistic networks” by Wesley Dattilo and coworkers.

In tropical environments, ant diversity is extremely high, reaching approximately 500 species at local scales. Because of both their abundance and diversity, it is extremely common to see ants foraging on plants. Within a spatial environment with a remarkable diversity (eg. Amazon rainforest) different plant and ant species can interact with each other and generate complex ecological networks of interactions. In this study, we studied how ants and plants with extrafloral nectaries interact over space, and we show that although the ant and plant composition of networks changed over space, the highly connected plants and ant species, and the structure of networks remained unaltered on a geographic distance of up to 5,099 m in the southern Brazilian Amazon. These finding indicate that different populations of plants and ants can interact in the same way independently of variation in local and landscape environmental factors. Therefore, our study contributes to understanding of the maintenance of biodiversity and coevolutionary processes in ecological networks.

Ants collecting extrafloral nectar on a plant in the fieldwork.

Ants collecting extrafloral nectar on a plant in the fieldwork.

Wesley Dáttilo collecting ant-plant interactions in the southern Brazilian Amazon

Wesley Dáttilo collecting ant-plant interactions in the southern Brazilian Amazon

Posted by: oikosasa | May 31, 2013

Welcome Sa Xiao, new Oikos Editor!

We also welcome Dr. Sa Xiao, Associate Professor at School of Life Sciences, Lanzhou University China. Learn more about him below and on his website

Sa Xiao1

What’s you main research focus at the moment?

My research interests mainly focus on the theoretical ecology and plant ecology. I am particularly interested in the areas of competition and facilitation, species coexistence and diversity, community structure and function. I use computer simulation model as the main research tool, especially the individual-based model programmed with multi-agent modeling language Netlogo. My current researches investigate the relative contributions of neutral theory’s process and niche theory’s process in explaining the multiple empirical patterns at the community-level, such as diversity-productivity relationship.

Can you describe you research career?

I took my PhD at School of Life Science here at Lanzhou University in 2006, where I have been Assistant and Associate Professor since then. In 2009-2011, I did a post-doc in Richard Malet’s lab nin Bordeaux, France. And I have been a Visiting Professor  in Ragan Callaway’s at University of Montana lab during 2010.

 How come that you became a scientist in ecology?

When I was in high school, I had a naïve belief that “Darwin’s theory solved the problems of living nature, and Marx’s theory solved the problems of human society, whereas how to solve the problems between human and nature? This should be the responsibility of ecologist”. So I decided to choose ecology as my life-time career.

 What do you do when you’re not working?

I like cooking very much and I’m particularly well versed in cooking Chinese food. I have strong interest in traditional Chinese philosophy such as Confucianism, Taoism, Yi- ology and Zen. I also like pop music, table tennis and swimming.

And a selected paper:

Xiao, S., Callaway, R.M., Newcombe, G. and Aschehoug E.T. (2012) Models of experimental competitive intensities predict home and away differences in invasive impact and the effects of an endophytic mutualist. The American Naturalist 180, 707-718.

Posted by: oikosasa | May 28, 2013

Welcome Mei Sun, new Oikos Editor!

We’re very happy to welcome Dr. Mei Sun, School of Biological Sciences, University of Hongkong to our editorial team!
Get to know Mei Sun here:
What is your research interest?
My main research focus at the moment is on plant speciation mechanisms and biological or other features that facilitate the rate of evolutionary diversification of angiosperms, especially in the family Orchidaceae as well as the Rhizophoraceae.
Can you describe your research career?
I became interested in plant ecology when I was an undergraduate working on a final-year thesis project in the field. During my postgraduate studies at the University of British Columbia, I become more interested in plant evolutionary biology. My Ph.D. research was on evolutionary genetics of Hawaii endemic species of Bidens (Asteraceae), a morphologically and ecologically diverse group arising from a single long-distance dispersal event followed by adaptive radiation into a variety of habitats on the Hawaiian Islands.
What made you become a scientist in ecology?
I am a molecular ecologist in the broad sense. Using various molecular marker systems, We aim to address various evolutionary questions, such as the investigations of genetic structure and outcrossing rates of hermaphrodites in natural populations of Bidens to determine whether inbreeding depression is one of the major factors in the evolution and maintenance of gynodioecy (e.g., Sun & Ganders 1986 Evolution); genetic diversity and evolutionary origin of Spiranthes orchids in Hong Kong (e.g., Sun 1996,1997 American Journal of Botany; Sun 1996 Conservation Biology); genetic resources and crop evolution (e.g., Amaranthus, sweetpotato, and rice); natural hybridization and phylogeography of Rhizophoraceae. More recently, I am also interested in comparative genetic analysis to understand the evolution of invasiveness in plants that are exchanged between SE Asia and Americas.
What do you do when you’re not working?
Reading about any subject that catches my attention at the moment; listening to soundscape music; watching TV; and doing Yoga …
For a recent representative publication:  please see
Mei Sun, Eugenia Y. Y. Lo   2011
Research Article | published 11 May 2011 | PLOS ONE 10.1371/journal.pone.0019671
Posted by: oikosasa | May 24, 2013

Can native species be invasive?

What should be included in the term “Invasive species”? In the new Early View Forum paper “Another call for the end of invasion biology”, Loic Valery discusses the issue. Here is a short summary of the paper:

The bulk of the literature devoted to biological invasions ignores native species and restricts the field of study to only introduced species. This split used by many researchers to justify the emergence of a distinct discipline is increasingly openly challenged.

Based on the etymology of the word “phenomenon” (i.e. what is seen, what is perceived by the senses), we show that a biological invasion manifests itself, always and only, by the rapid appearance of a state of dominance of a species. Therefore, there is no reason to take into consideration other factors (in particular, the biogeographical origin of the invader) that prove to be both inappropriate and inoperative from a theoretical and practical viewpoint, respectively.

Thereby removing any justification for the autonomy of invasion biology, we advocate a more integrated study of all species on the move.

Sus scrofa_A. MauxionElymus athericus_A. Mauxion

Invasive species can also be native. Here are two examples of native invaders in Europe:  the sea couch grass Elymus athericus Link spreads in salt marshes, from high marsh towards middle and low parts where it forms large dense monospecific stands (here, in the Mont-Saint-Michel bay); and  the wild boar Sus scrofa L., whose populations have exploded demographically in forests and agricultural systems, now extends in big cities such as Berlin, Milan or Barcelona for foraging. (Photographs: courtesy of André Mauxion).

Posted by: oikosasa | May 21, 2013

Even the small ones are important!

Size is not all! Even small herbivores have effect on plant community, as shown in Salvador Rebollo and co-workers new Early View paper shows: “Disproportionate effects of non-colonial small herbivores on structure and diversity of grassland dominated by large herbivores”.

Here is a summary of the study by Rebollo:

Daniel G. Milchunas and Salvador Rebollo, two out of five authors of the article, along-side a large-plus-small herbivore exclosure in the shortgrass steppe.  We tested our hypotheses over a 14-year period in pastures grazed at moderate intensities by cattle and in two types of exclosures: for large (barbed-wire) and for large-plus-small herbivores (small-mesh hardware cloth).

Grasslands are grazed by a complex assemblage of herbivores that differ in body size, abundance, diet, and foraging strategies.  Grazing studies have most often examined effects of large herbivores, probably due to their greater amounts of plant consumption and economic importance.  Studies of small herbivores have focused on social, central-place foragers that reach high local densities and build conspicuous burrow systems, such as prairie dogs or European rabbits.  The role of more evenly dispersed small herbivores in structuring vegetation, especially in perennial grasslands, has been less studied.  What is the importance of these cryptic small herbivores?

Our research was conducted in the semiarid shortgrass steppe of the North American Great Plains, a grassland with a long evolutionary history of grazing by large generalist herbivores and one of the most tolerant ecosystems to grazing by these herbivores.  This ecosystem is considered marginal habitat for small herbivores (except for the social and colonial prairie dogs) due to the lack of overhead cover, the low seed-to-vegetation production ratios, and small seeds of the dominant plant species.  Peak biomass and consumption of rodents and rabbits was estimated to be a fraction (<8%) of that of large herbivores.  We hypothesized that 1) large generalist herbivores would affect more abundant plant species and proportions of litter (old fallen vegetation), bare ground, and vegetation cover through non-selective herbivory, and 2) small herbivores would affect cover and richness of less abundant species, through selective but limited consumption.

Photo 2

Vegetation in one of the large-plus-small herbivore exclosures. Exclusion of herbivores of both body sizes had complementary and additive effects that were linked to increased abundance of tall and decreased abundance of short plant species. Uncommon species as a group were not affected by the additional exclusion of small herbivores, but the tall annual Tragopodium dubious (compositae plant located in the front part of the photo), was an example of one uncommon species that did increase with small herbivore exclusion.

David Augustine conducts a prescribed burn in shortgrass steppe at the Central Plains Experimental Range.

David Augustine conducts a prescribed burn in shortgrass steppe at the Central Plains Experimental Range.

The study site was at the Central Plains Experimental Range (CPER) in northeastern Colorado, USA, one of the Long Term Ecological Research (LTER) grassland sites (Photos 1 and 2), as well as a Long-Term Agro-ecosystem Research (LTAR) network site.  We found that the exclusion of large herbivores affected litter and bare ground, and basal cover of abundant, common, and uncommon species.  Contrary to our hypothesis, additional exclusion of small herbivores did not affect uncommon components of the plant community, but had indirect effects on abundant species, decreased the cover of the dominant grass Bouteloua gracilis (blue grama) and total vegetation, and increased litter and species diversity.

Paul Stapp handles a thirteen-lined ground squirrel, one of the most common small mammal species in shortgrass steppe at the Central Plains Experimental Range.

Paul Stapp handles a thirteen-lined ground squirrel, one of the most common small mammal species in shortgrass steppe at the Central Plains Experimental Range.

Our findings show that small mammalian herbivores had disproportionately large effects on plant communities relative to their small consumption of biomass.  Grazing by the combination of large and small herbivores favored recovery of short grasses after extreme droughts, providing resilience to the shortgrass steppe and contributing to the long-term maintenance of vegetation basal cover.  Our study expands prior work about small herbivores and demonstrates that even in small-seeded perennial grasslands with a long history of intensive grazing by large herbivores, non-colonial small mammalian herbivores should be recognized as an important driver of grassland structure and diversity.  Therefore, the importance of small herbivores was greater than initially thought and their effects on plant communities, isolated or in interaction with large herbivores, should be part of an integrated theory of how about herbivores influence grassland diversity.

Photo 5

Justin Derner sorts yearling steers for grazing experiments (and provides comedy relief) at the Central Plains Experimental Range.


Posted by: oikosasa | May 17, 2013

Habitat complexity, preys and predators

In the new Early View paper “Trait-mediated indirect interactions in a marine intertidal system as quantified by functional responses”, Mhairi E. Alexander and co-workers, have studied how factors as habitat compelxity affect predators and how the predators effect prey populations. Here’s their own summary:

It is well known that predation is important in community structure and functioning. It is also understood that the impact of a predator can be influenced by a number of biotic and abiotic factors. For example, the presence of higher-order predators can influence behaviours of intermediate species that can affect their consumption of prey through trait-mediated effects. Habitat complexity can also be an important mediating influence that in turn can influence the numbers of prey that are consumed. What is less well understood however is how these factors interact and contribute to prey population stability. In this study we address this by detecting and quantifying such trait-mediated indirect interactions (TMIIs) using functional responses, which consider a predator’s consumption over a range of prey densities, to investigate the implications for prey population regulation and stability,


We conducted several experiments to investigate how the influence of a higher-order fish predator combined with habitat complexity affects the behaviour of an intermediate amphipod predator from marine intertidal habitats. We first tested whether amphipods were able to determine higher-order predator presence. We found that amphipods demonstrated anti-predatory behaviour via a reduction in activity with the addition of cue that was seawater mixed with crushed conspecifics as well as seawater from tanks holding fish fed conspecifics and also those fed bloodworm. Interestingly, there was no reaction to fish fed an algal diet or those that had been starved. As we didn’t find any response of the basal prey, a commonly occurring isopod, to these cues, we went on to investigate how the presence of the cue in combination with habitat complexity affected the amphipods predation rates and whether the observed reduced activity translated into reduced foraging.


We observed that when there was no habitat or fish cue, amphipods showed what are considered to be potentially destabilising predatory responses towards the isopod prey. With the addition of habitat, however, the response was found to become stabilising as a result of a reduction in consumption of prey at low densities.  When habitat complexity was not included, the presence of fish cue was found to reduce the magnitude of the predator’s consumption of prey at higher densities, as would be expected with reduced activity in the presence of a predator. However when habitat was present in combination with fish cue, although reduced consumption occurred at low densities, at high prey densities it was increased in comparison to predation with habitat complexity and no cue. This seemed to occur as the fish cues drove the amphipods into habitat with more prey and thus actually enhanced predation of the basal prey.

The results from this study demonstrate the utility of functional responses in addressing questions of prey population stability. In addition we have further highlighted how complex predator-prey interactions can be, as well as exploring the relevance of environmental and biological cues that can result in unexpected and complex outcomes.

Posted by: oikosasa | May 14, 2013

Editor’s choice May

DriesOikos will publish synthetic meta-analyses open access and with high priority, and has assigned Christopher Lortie as deputee editor responsible for handling and inviting such contributions.  Jodi Price and Meelis Partel used meta-analyses to examine experimental evidence that functional similarity between invaders and resident communities reduces invasion. They found evidence for forb species but not for grasses, but equally important, their study highlights the fact that such patterns are more prominent in artificially assembled communities than in more natural communities with species or functional groups removed. Only by synthesing data from multiple studies the authors can unambiguously demonstrate that ecological mechanisms that are both theoretically and empirically underpinned may be only limited expressed under natural settings.

As a second editor’s choice we selected a theoretical study by Sonia Kefi and co-authors exploring to which degree critical slowing down is a key phenomenon to measure the distance to a tipping point in ecosystems. Tipping points are abrupt, unexpected and irreversible shifts within ecosystem. Specific ecosystem characteristics like spatiotemporal changes in biomass or population sizes may provide hints or early warning signals about an approaching shift. There is indeed a quickly expanding literature suggesting the presence of such early warning signals. By using analytical modelling, the authors demonstrate that -contrary to the ruling perspective- early warning signals based on critical slowing down are representative for a broader class of situations where systems experience increasingly sensitivity to perturbation. They are hence not solely specific to catastrophic shifts. This study consequently warns for a careful interpretation of critical slowing down as an early warning signal. It thereby stimulates further research aiming at developing and interpreting alike indicators to catastrophic ecosystem shifts whose occurrence may be extremely important for the livelihood of people living in such threatened ecosystems.

Editor’s Choice papers are freely accessible online for three months.

Posted by: oikosasa | May 7, 2013

Top of the pops

One of the most cited papers in Oikos, during 2011 (published 2009 and 2010) is “Life history tradeoffs influence mortality associated with the amphibian pathogen Batrachochytrium dendrobatidis”  Trenton W.J. Garner and co-workers. Here, Trent gives a short summary about the paper and tries to explain why it has been so important.


The chytridiomycete fungus Batrachochytrium dendrobatidis is a potentially lethal parasite of amphibians considered by many to be a primary factor behind global amphibian declines. It’s been associated with mass mortality and amphibian species decline on four continents and is the subject of a heck of a lot of research effort. However, at the time of the work, almost no published studies had attempted to test hypotheses developed from field observations of infection and mortality, and none had done so using both robust experimental design and multiple life history stages. The study was a real team effort, incorporating the results of extensive field work, multiple experiments and a concerted effort to isolate the parasite from field mortalities. While the results of experiments broadly supported the conclusions derived from field data (infection and death are predominantly related and Batrachochytrium dendrobatidis is likely the cause of post-metamorphic mass mortality events of common toads Bufo bufo in Spain), some previously unconsidered dynamics were revealed. We found that increased mortality was associated with weaker doses of the fungus, but often when infection did not appear to have occurred. We have since shown this to be the case in another amphibian species (Luquet et al 2012 Evolution).

Exactly how the risk of mortality can increase without detectable infection at time of death remains uncertain, but this is certainly different from what is seen in highly susceptible host species, where the burden of infection correlates positively with increased risk of death. As well in our study decoupling of infection from mortality was only detected in larvae. Previous to this, the tadpole stage was primarily overlooked as a stage susceptible to any substantial costs imposed by chytridiomycosis. This is because the parasite requires superficial keratinized tissue to proliferate, and this kind of keratin is only ubiquitously available on host anurans after metamorphosis, when the keratinized stratum corneum is fully developed. I think this may be the most interesting part of the study, that potentially lethal costs may be accrued by a host species even when the tissue that is the primary target for infection is still not fully available to the parasite.

For me one of the most satisfying outcomes of this study has been the ability to export the experimental methodology to other labs, which we have done through our EU-funded project RACE (Risk Assessment of Chytridiomycosis for Europe’s amphibians, Several researchers in several countries have benefitted from using techniques developed during this study, most importantly several graduate students. We’ve also employed our experimental system to explore relationships between climate change and chytridiomycosis (Garner et al. 2011 Global Change Biology) and investigate the evolution of the fungus itself (Fisher et al. 2009 Mol Ecol, Farrer et al. 2011 PNAS). In doing so, I believe we’ve been able to shine some light on the rather unpredictable and context-dependent relationships between Batrachochytrium dendrobatidis and amphibian hosts that are not highly susceptible to chytridiomycosis, but may still experience the lethal form of the disease.

We use cell culture flasks to house tadpoles individually through metamorphosis. This system allows us to replicate extensively while keeping the individual animal the unit of replication. Replicating treatments 30 or 40 times is easily achievable for most experiments using this approach. Not bad for a vertebrate.

We use cell culture flasks to house tadpoles individually through metamorphosis. This system allows us to replicate extensively while keeping the individual animal the unit of replication. Replicating treatments 30 or 40 times is easily achievable for most experiments using this approach. Not bad for a vertebrate.


Posted by: oikosasa | May 6, 2013

Oikos at INTECOL

INTECOL 2013, takes place in London August 18-23, see

We’ll be there! Will you?

More info on Oikos symposium and other activities will come soon!

The 11th INTECOL Congress, Ecology: Into the next 100 years will be held in London as part of the centenary celebrations of the British Ecological Society.The theme of the Congress is Advancing ecology and making it count.

Early-bird registration closes on 12th May:

Read about butterflies finding romance in the mountains in the new Early View paper “Simple rules for complex landscapes: the case of hilltopping movements and topography” by Guy Peer and colleagues. here’s Guy’s summary of the paper:

Mating on a hilltop

Mating on a hilltop

You are lost in an unfamiliar, hilly landscape. What shall you do? Most people would ascend the nearest hill and try to get a good overview. Butterflies may have much more limited vision, but they manage quite effectively in aggregating on mountain tops which serve as rendezvous for mating. An individual-based model which focuses on this “hilltopping” phenomenon identifies simple behavioural rules that can optimise mating success, and the success of mated females in finding habitat patches, across landscapes regardless of their complexity. One interesting rule is: when moving uphill, butterflies should respond strongly but not ‘perfectly’ to topography. A perfect response, without occasional random movements, would simply trap them on local summits. If such mild randomness might be adaptive, shall we adopt the rule and accept our imperfections? At least for butterflies, it clearly helps finding a mate.

Fighting overe a female on a hilltop

Fighting overe a female on a hilltop

Guy Pe’er when chasing hilltopping butterflies in Israel, long ago when doing his PhD. While his “hilltopping model” is by now 12 years old, new results continue to emerge.

Guy Pe’er when chasing hilltopping butterflies in Israel, long ago when doing his PhD. While his “hilltopping model” is by now 12 years old, new results continue to emerge.
Posted by: oikosasa | April 23, 2013

The zombie killing spree continues

Look up, zombies are all around us nowadays! Even within science! In the Early View paper  “A critical analysis of the ubiquity of linear local–regional richness relationships“, Thiago Goncales-Souza and colleagues  goes on a zombie-killing adventure. Here is there summary of the paper:

Recently, ecologists have gone on a zombie killing spree, started by a blog post of Jeremy Fox here at the Oikos blog (link here). Dr. Fox defined zombie idea as having “survived decades of attacks from the theoretical and experimental equivalents of chainsaws and shotguns, only to return to feed on the brains of new generations of students.” He featured other zombie ideas such as “neutral = dispersal limitations” and the unimodal diversity productivity relationship. The post on his original zombie idea actually resulted in a peer-reviewed publication (Fox 2013) that, in his own words, has “No zombie jokes or other inflammatory rhetoric in it. I leave it you to judge if that makes the paper better or worse than the blog posts.” (link here).

We think that our publication fits into this zombie killing tradition. One of the most fundamental interests of ecologists since the early development of the ecological theory is the understanding of (potential) processes that drive local community structure. At a fundamental level, communities are structured by a combination of local environmental and regional processes (Ricklefs 1987).  The easiest and most traditional way to test whether regional or local processes affect local community structure consists of regressing local against regional species richness (the famous LSR-RSR relationships). The argument goes that communities controlled by regional processes are considered unsaturated, whereas communities controlled by local processes (such as species interactions) are considered saturated. Sadly enough, this argument survived indeed decades of attack (D. Srivastava, F. He and collaborators, and H. Hillebrand).

Sadder still, this method has kept on feeding on the brains of new generations of students, since it is used and featured prominently in ecology textbooks such as Begon et al. (Ecology: from individuals to ecosystems), Krebs (Ecology: the experimental analysis of distribution and abundance), and Ricklefs (The Economy of Nature and Ecology). Probably every ecology student has heard about the ubiquity of regional processes as drivers of local community structure using this method.

In addition to these fundamental problems, Szava-Kovats and collaborators in Oikos showed that the statistical test for detecting the linearity of the relationship is biased towards linear relationships, and moreover provided an unbiased method (called log-ratio method). In this Forum paper, we reevaluated the evidence for the ubiquity of linear LSR-RSR relationships by comparing the biased conclusions with the unbiased method, and found:

  1. In 113 relationships found in 47 studies, 70% and 30% were considered unsaturated and saturated, respectively, when using the biased method. However, by using the unbiased log-ratio method we found no prevalence of either unsaturated (53%) or saturated (47%) communities (Figure 1);
  2. 40% of the studies using the biased method were misclassified (i.e., mistakenly found an unsaturated pattern when it was saturated or vice-versa) and thus reached wrong conclusions.
  3. 50% of the examples of LSR-RSR relationships used in four (classic) ecology textbooks were misclassified.

Our conclusions thus add a new weapon in the arsenal against the zombie idea of interpreting local-regional relationships based on the linearity of the relationship. We showed that the last argument in favor of the method (its ubiquity) was based on a biased statistical method. We argue instead that future studies should consider the reciprocal interactions between regional and local such as those that take advantage of the metacommunity theory to understand the relative influence of regional and local processes on local community.

While studies of LSR-RSR relationships were instrumental to the development of the ecological curriculum, we hope that we can now finally put this zombie idea to rest and move on. As a final note, one of the reviewers for this manuscript was … non other than Jeremy Fox, zombie slayer par excellence.


Posted by: oikosasa | April 18, 2013

Welcome Susan Harrison – new SE

We are very happy to welcome Prof. Susan Harrison from UC Davies, USA, to our editorial board.
 susan at sensitive plant canyon 

My research seeks to understand the processes that shape and maintain plant species diversity at the landscape scale, where small-scale forces such as competition and facilitation interact with large-scale forces such as niche evolution and dispersal.  In the past few years, one particular focus has been to understand what characteristics of plant species and communities make them more or less susceptible to climate change, as well as to other interacting perturbations like fire, grazing, and invasion.  We’ve found that plant communities on nutrient-poor serpentine soils seem to respond less strongly to natural and experimental climatic variation than other communities, but we don’t yet understand the roles of soil properties, plant traits, and emergent community properties in causing this pattern.

Read more:

GG burn wildflowers 7
Posted by: oikosasa | April 16, 2013

Same, same but oh so different.

They look the same, but perform so differently. And act differently against each other. Cryptic amphipods are dealt with in the Early View paper “Phenotypically similar but ecologically distinct: differences in competitive ability and predation risk among amphipods” by Rickey D. Cothran and colleagues. Read their summary here:

Traditionally, species that look alike were thought to be unlikely co-inhabitants due to competitive exclusion. However, newer theory suggests that a mix of ecological similarity that limits performance asymmetries that lead to competitive exclusion and slight differences in niche use may maintain species diversity. We provide data on the relative competitive ability and predation risk for three amphipod species that co-occur in lakes in North America. Until recently, these species were only differentiated using molecular markers (see picture). We discovered that slight differences in phenotype lead to differences in how well these species compete and deal with predators. We also found that the two species that show the strongest overlap in distribution within lakes are very similar when it comes to their competitive ability and predation risk. Our work suggests that a mix of niche differentiation and ecological similarity are maintaining amphipod species diversity in lakes.

 Cryptic amphipod species before (top) and after (bottom) preservation in 70% ethanol. From left to right: species A, species B, and species C. All animals are females.

Cryptic amphipod species before (top) and after (bottom) preservation in 70% ethanol. From left to right: species A, species B, and species C. All animals are females.

Picture caption: Cryptic amphipod species before (top) and after (bottom) preservation in 70% ethanol. From left to right: species A, species B, and species C. All animals are females.

Posted by: oikosasa | April 11, 2013

Taking metacommunity models to the empirical world

Will the use of “real” connectivity between communities improve metacommunity models? Read more in C.Moritz and colleague’s Early View paper: “Disentangling the role of connectivity, environmental filtering, and spatial structure on metacommunity dynamics”. Here’s their summary of the paper:

For decades, the environment has been proven to structure biodiversity. However, dispersal of organisms is also  a process that helps structuring and maintaining biodiversity in local communities. The problem is that  connectivity between communities (the fact that these communities are linked, resulting from the dispersal  process) is often assessed using a more or less simple function of geographic distance. Theoretical metacommunity models can incorporate both environmental and dispersal processes, but empirical  studies considering real connectivity instead of a function of geographic distance are more scarce. In our work,  we have included real connectivity measures to analyse polychaete community structure in the Gulf of Lions (NW  Mediterranean Sea) at different spatial scales. Our results are not trivial…and equivalent methods should be  applied to other ecosystems (terrestrial or marine) to continue quantifying the importance of dispersal on  biodiversity, either for particular species of interest or for entire communities.


Posted by: oikosasa | April 9, 2013

When plants help other plants…

Nice to see that nature provides other kinds of interactions than nasty predation, competetion and parasitism! Christian Schöb and coworkers have studied the importance of “nursing” plants – plants that fascilitate for other plants – in community ecology. Read their Early View paper “Direct and indirect interactions co-determine species composition in nurse plant systems”.

Here is a summary of their study:

Our motivation to build a framework based on observational data in order to disentangle direct nurse effects from indirect effects among beneficiary species was twofold:

1) In some very common nurse plant systems, such as alpine cushion plant communities, the removal of the nurse to eliminate the direct effect and unambiguously estimate interactions among beneficiary species is simply not feasible.


The physical removal of the nurse cushion Arenaria tetraquetra ssp. amabilis growing in the Sierra Nevada Mountains in Spain would destroy the beneficiary species growing within the cushion canopy; in particular because beneficiary species often root in the organic matter accrued under the cushion.

2) Even in nurse plant systems where the physical removal of the nurse is feasible, taking away aboveground nurse parts does not remove the permanent effects of the nurse, e.g. the effects on soil properties including texture, resources and microbial communities.

An intact Retama sphaerocarpa nurse plant system in the semi-arid lowland of southeastern Spain with the nurse shrub and its understory community of beneficiary species.

An intact Retama sphaerocarpa nurse plant system in the semi-arid lowland of southeastern Spain with the nurse shrub and its understory community of beneficiary species.

The removal of aboveground parts would not remove the whole effect the nurse shrub, such as accumulation of soil organic matter and its specific communities of soil bacteria and fungi, which all together influence beneficiary species even after the nurse plant has been removed.


In our article we propose a simple but powerful mathematical framework to take apart direct effects of the nurse on its associated community from effects of interactions among beneficiary species. Our results showed facilitative effects of the nurse on its beneficiary species whereas interactions among beneficiary species where mostly competitive. Both interactions contributed significantly to the composition of the beneficiary plant community even though the direct nurse effect was ca. five times stronger than the effect of the interactions among beneficiary species. Interestingly, these patterns where similar in the two nurse plant systems studied even though they differed considerably in abiotic conditions (high alpine vs. semi-arid lowland) and growth form of the nurse (cushion plant vs. shrub). Our data therefore indicate functional parallelism of different nurse plant systems and highlight the complexity of species interactions within plant communities.

Hello everyone, my name is Ross Boucek and I am PhD student at Florida International University. Oikos has asked me to write about our Early View paper “No free lunch: displaced marsh consumers regulate a prey subsidy to an estuarine consumer” where we investigate the value of food subsidies to recipient consumers as well as what controls the amount of food subsidies available to them.  Food subsidies are resources that enter an ecosystem from another place, and add on to the resource base that is already available within the system. Subsidies in some instances can be almost considered a bonus, like getting cash for your birthday in the mail.  If you are on a graduate student stipend, birthday cash subsidies can go a long way! Because of the predictability of birthday cash, many graduate students budget these cash bonuses into their spending well before they arrive.  Therefore, if for some reason these checks get lost in the mail, or they are for less money, we could be in some trouble!

Graduate students and their reliance on birthday money is very similar to how some animals rely on food subsidies to survive.  One particularly charismatic example of consumer-subsidy interaction is bears and salmon in the U.S. Pacific Northwest.  In the fall, these bears congregate around rivers and streams to gorge themselves on salmon that predictably migrate from the oceans to spawn. These salmon subsidies help bears build necessary fat reserves that play a major role in their survival and reproduction over the winter. Because of the importance of food subsidies to consumers, biologists and ecologists have gone to great lengths to identify where subsidies occur in nature, and more importantly what controls how much of the food subsidies reach recipient consumers.


Diagram of the relationship between marine salmon subsidies and bears

Moving back to the bear-salmon subsidy interaction, in some areas of the U.S. Pacific Northwest, sea lions have figured out salmon are easy prey during their spawning migration; such that some sea lions track salmon up rivers, and pig out on these spawning fish, preventing them from reaching bears. The interception of these salmon subsidies by sea lions can be so intense, that they can reduce salmon available to hungry bears waiting upstream by as much as 65%.

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Diagram showing how sea lions reduce salmon subsidies to bears

This brings me to my research.  I work in the Florida Everglades, more specifically, where the iconic Everglades marshes or the “river of grass” joins the beautiful tropical mangrove estuary.


The study area of our research, located at the marsh-estuary interface in the Southwest Everglades

At this interface between the marsh and the estuary, during the winter and spring, rainfall decreases, causing freshwater marshes to dry.  When these marshes dry, large numbers of small-bodied freshwater fishes are forced into the estuary. At the same time that these prey enter the estuary, estuarine fish predators triple in abundance presumably to gorge on the marsh fish prey forced into the estuary.  Thus at the Everglades ecotone, estuarine predators function similarly to the bears in the Pacific Northwest, and small bodied marsh prey are like the salmon. However, similar to the sea lions, these small bodied fishes are accompanied by large-bodied fish predators that also live in the marsh that can intercept and remove or reduce fish prey subsidies to the estuarine consumers.  With all of this in mind, my research questions were 1) how important are marsh prey subsidies to estuarine consumers? And 2) how much of this subsidy is being removed by marsh predators?


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Diagram showing the relationsship between estuarine and marsh predators and marsh prey subsidies at the marsh-estuarine interface of the southwest Everglades

Our results show, like the salmon-bear example, that estuarine predators gorge themselves on these marsh prey subsidies. Consequently, the consumption of this subsidy makes estuarine predators roughly 15% fatter than they were before.

However, like the sea lion example, freshwater marsh predators consume about 60% of the fish prey that enter the estuary, leaving only 40% for the estuarine consumers.   The regulation of this subsidy to snook, the estuarine predator, could influence how much energy snook allocate to reproduction each year.  Snook spawn in the early summer to mid fall. Therefore the weight snook gain from this subsidy in the spring could go to egg production in the summer, thus increasing reproductive output.  If marsh predators decrease in abundance, then the amount of subsidy available to snook could increase, which may allow snook to invest more energy into reproduction and increase spawning success.  My current research is investigating just this question, whether or not larger prey subsidies, facilitated by the loss of marsh predators, result in increased spawning effort by snook.

Understanding the dynamics behind this subsidy could have important implications for South Florida.  In South Florida, snook are an important recreationally sought after fish.  In fact, snook are the 5th most targeted fish in the entire east coast of the United States, despite only occurring in South Florida. The money spent from anglers fishing for snook generates substantial amount of revenue for local businesses.  Therefore, knowing the drivers behind snook population dynamics like the regulation of food subsidies will help us better understand the provisioning of ecosystem services such as fisheries in the Everglades.


Posted by: oikosasa | April 2, 2013

Large-scale testing of Bergman’s rule

The colder, the bigger, suggested Bergman in 1848. In 2013 we publish a paper testing Bergman’s rule on a large data set. Showing…well find out in “Bergmann′s rule in mammals: a cross-species interspecific pattern” by Marcus Clauss and his co-workers. Below is their background story to the study:

I first learnt about ‘Bergmann’s rule’ (that among closely related species, those living at higher latitudes/at colder temperatures are larger) in school. It was one of the biological facts I had always considered a background fact that is unquestioned.  

When preparing a manuscript on the reproductive seasonality of ruminants (Zerbe et al., 2012) we collated various biological data on ruminants, including body mass and mid-latitude of their geographical range, and before testing relationships of these data with our proxy for seasonality, we tested them amongst themselves for potential correlations. We did this without accounting for the phylogenetic structure of the data (ordinary least squares) and with such an accounting (phylogenetic generalized least squares, pgls).


We were not surprised when we found a relationship between latitude and body mass in our phylogenetic analysis – because this simply reflected Bergmann’s rule. The fact that this relationship was not significant in conventional statistics, but significant in pgls, just supported the notion that the rule holds among closely related species, not just any species you lump together. For us, this was a minor side-dish result in our set of analyses, and one we were not excited about, because it simply confirmed what we knew from school. In a quite similar way, our ruminant dataset supported, for example, Rensch’s rule (which was cool for our co-author that had the same name). But when we prepared the manuscript, and searched for other papers to cite in connection with our side result, we realized that Bergmann’s rule had, as far as we could find, not been analysed in this fashion among mammal species, not in ruminants, and surely not in a larger mammal dataset. Literature on Bergmann’s rule in mammals most often dealt with the intra-specific side of the phenomenon or with mammal assemblages, but not on the taxonomic/interspecific level. So we expanded the dataset beyond the ruminant species for which we had seasonality data, to comprise all mammals (based on availability of data in the PanTheria database). Again, we found the same effect: the relationship between latitude and body mass was significant if the phylogenetic structure of the dataset was taken into account. In a sense, we felt like having found a simple proof for a school lesson that had not been provided so far. This does not mean we claim to be first, best, closest, whatever, to proving Bergmann’s rule – we just found a simple, maybe elegant way to demonstrate it. Actually, once you start looking at individual taxonomic subgroups or certain geographic ranges, the picture becomes less simple – but that’s in the paper.  

For us, several lessons came with working on this topic. One is that the statistical procedure (pgls, sometimes called ‘phylogenetically controlled statistics’) is not only a quarrelsome one that one has to apply nowadays to get a paper published, but actually facilitates, in special circumstances, the detection of a pattern that would not be evident from simply plotting the data, or from ‘conventional’ statistics. So we tried to understand how patterns would look that yield different results in conventional and phylogeny-informed statistics, drawing on textbooks on the matter, and produced some schematic graphs to get a mental grasp on this (provided as a supplement to our paper). In my experience, there are quite some examples where a relationship that is significant in conventional statistics is no longer so in phylogenetic statistics (which then needs to be interpreted), but there are very few examples where a relationship is not significant in conventional stats but clearly is in phylo-stats.  

The other lesson came from going through the literature – at some stage, we decided to try to locate the original source itself, Bergmann’s own account, which was sometimes described as ‘hard to get at’ – and were surprised that you could simply download the whole text from the net (it is now part of the google books resource pool). Reading this text was quite some fun, due to the old style it was written in. From other literature, we had gained the impression that Bergmann formulated his rule for mammals, and were therefore surprised to see that he actually developed it, and supported it, using birds. And all the examples Bergmann used himself were between, not within, bird species, so no need to debate whether he meant it on an inter- or intra-specific level. Because the text is written in German, we decided to provide a relatively detailed translation of larger parts of it, so that others could get a picture of how he built his argument. I personally especially cherished his concluding comment, where he cautions the reader that in trying to support his hypothesis, he might have looked at the actual evidence in a biased way, and that therefore independent tests would be welcome.    

Posted by: oikosasa | March 28, 2013

Editor’s choice April 2013

DriesFor the April issue, we chose the following two papers as editor’s choice according to our motto of synthesizing ecology. Mumby et al. (2013) discuss various articles that either support or reject the hypothesis that coral reefs might be able to exist under certain conditions in two alternative stable states (ASS): a coral-dominated and a macroalgae-dominated state. Given the fact that the existence of multiple attractors is controversial, synthesis needs to be created by compiling various forms of evidence. Mumby and colleagues provide such an overview of evidence by providing analyses of the literature and the available empirical and theoretical data. By means of this integrated approach, they conclude that the most compelling evidence, which combines ecological models and field data, is far more consistent with multiple attractors than the competing hypothesis of only a single, coral attractor. This message warns managers that degraded reeds might never be able to be restored once dominated by macro-algae. Read Peter Mumby’s summary of the paper here

The second paper we selected is Baiser et al. (2013) testing the ability of metacommunity models to predict the network structure of the aquatic food web found in the leaves of the northern pitcher plant Sarracenia purpurea. It is the central aim of metacommunity theory to elucidate the relative impact of local and regional processes on local community structure. The structuring processes have, however, been predominately inferred from statistical modelling. The work of Baiser and colleagues takes an elegant approach to formally test to which degree patch-dynamics, species-sorting, mass-effects, and neutral metacommunity models, as well as three hybrid ones are able to predict observed patterns of the aquatic foodweb structure within these plants. By merging empirical data and more mechanistic models they test the probability that dispersal and sorting processes are important mediators of food web structure. While such integrated empirical-theoretical approaches have been developed for other ecological questions, Baiser et al. here demonstrate its usefulness for understanding drivers of food web structure.

Both papers as Open Access.

Posted by: oikosasa | March 26, 2013

New Oikos Cover!!

From the April issue 2013 onwards, Oikos will have a photo illustrating ecology in action on it’s cover.

To find the right photo for this year’s cover, we had a photo competition during winter. The happy winner of the competetion is Sascha Rösner, Marburg, Deutschland. See more of his photos here:

And here is our new cover:


And here, Sascha tells us how he took the winning photo:

Wildlife photography often entails long travels to distant and remote landscapes that harbour a particular species of interest. This picture of two sawfly caterpillars (Nematus spec.), however, was taken just three meters of the front door of the photographer’s home. In the front yard, a small willow tree (Salix spec.) was densely populated with hundreds of these caterpillars. An easy opportunity to take the camera from indoors, attach a macro lens to the camera, mount it on a tripod, and take pictures (in fact, still wearing slippers). By chance, two of these guys apparently fed synchronously in the center of a leaf. Within 24 hours, the tree was completely naked, the caterpillars “abseiled” to the ground, and dug into the soil where they would morph into the imago flies some weeks later. Canon EOS 20D, EF 100 mm 2.8 @ f 7.1, ISO 100, tripod, remote control.

Posted by: oikosasa | March 22, 2013

Time to get rid of the males?

It has been debated for a while…are males really necessary? Find out how fish of the genus Chrosomus solve the small problems associated with asexual reproduction, in the Early View paper “Diets of sexual and sperm-dependent asexual dace (Chrosomus spp.): relevance to niche differentiation and mate choice hypotheses for coexistence” by Jonathan A Mee and co-workers.

Here’s a short summary of the study:

In order to persist, sperm-dependent asexuals must be ecologically divergent and/or more sperm-limited compared to their sexually reproducing hosts.

It’s easy to be fascinated by sperm-dependent asexual species – they’re one of those oddities of natural history that, collectively, are the reason many of us became students of biology. These all-female “Amazons” require a male (or just their sperm) of a sexually reproducing host species to provide the trigger for egg development and reproduction, but, in most cases, discard the male’s genome.

In addition to being a fascinating natural oddity, the existence of sperm-dependent asexuals raises an interesting scientific question: how do sperm-dependent asexuals coexist with their host species?  All-female asexuals have a great advantage over sexuals – by producing no males, the asexuals have twice the potential population growth rate relative to the sexuals.  But, in the case of sperm-dependent asexuals, vastly outcompeting the sexuals (i.e., eliminating the source of sperm) would eliminate the ability to reproduce.  There are two general mechanisms by which sperm-dependent asexuals and their sexual hosts can achieve stable coexistence.  First, sufficient ecological divergence between the sexuals and asexuals would avoid competitive exclusion.  Second, if males prefer mating with sexual females rather than asexual females, asexual females would be more sperm limited (and have reduced reproductive output) relative to sexual females.

blog eos

Our contribution to understanding how sperm-dependent asexuals coexist with their sexual hosts examined the combined influence of these two mechanisms (ecological divergence and male mate choice) on the coexistence of sperm-dependent asexual species and their sexual hosts – previous work only considered each mechanism independently. We integrated the insights of mathematical modeling and empirical data on ecological divergence (from two natural populations of the sperm-dependent asexual fish, Chrosomus eos-neogaeus) to conclude that a combination of both mechanisms may be required for coexistence. This integrated approach is valuable to understanding many ecological and evolutionary processes.

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Posted by: oikosasa | March 19, 2013

On the evolution of fruit colour

Ever thought about why an orange is orange while an apple is green? And a blueberry blue and blackberry black, while a raspberry is red? Well, one explanation – seasonality – is studied in the new Early View Paper  “Fruit color and contrast in seasonal habitats – a case study from a cerrado savanna” by Maria Gabriela G. Camargo and co-workers. Here is their short summary of the study:


Examples of fruits with different colors. A. green; B. multicolored; C. yellow; D. black; E. multicolored; F. brown; G. multicolored; H. red.

Fruit color is an important signal for diurnal seed dispersers, mainly for birds, and the contrast between the fruit and the background is regarded as more important than the color per se for fruit detectability. However, the contrast between fruit displays and their background are not necessarily constant in seasonal habitats where part of leaves is shed in the dry season.

We thus hypothesized that the contrast between fruit displays and their background vary throughout the year in a seasonal habitat and if this variation is adaptive, we predicted higher contrasts between fruits and foliage during the fruiting season.

To verify our hypotheses we used reflectance measurements of fruits and leaves and contrast analysis. We also accessed a six-year data base of fruit ripening according to the fruit color (red, yellow, black, brown and multicolored) for a woody community in a cerrado-savanna vegetation, southeastern Brazil. The cerrado is subjected to a seasonal climate, with a wet summer between October and March and a dry winter between April and September, when the leaf background get yellowish.


Circular histograms for the frequency of fruiting onset dates per fruit colors in a woody cerrado savanna community, southeastern Brazil.

We found that black, and particularly red fruits, that have a high contrast against the leaf background, were highly seasonal, peaking in the wet season. Multicolored and yellow fruits were less seasonal, not limited to one season, with a bimodal pattern for yellow ones, represented by two peaks, one in each season. We further supported the hypothesis that seasonal changes in fruit contrasts can be adaptive because fruits contrasted more strongly against their own foliage in the wet season, when most fruits are ripe. Hence, the seasonal variation in fruit colors observed in the cerrado-savanna may be, at least partly, explicable as an adaptation to ensure high conspicuousness to seed dispersers.


Mean leaf reflectance curves during the dry and wet seasons for 49 species of the woody cerrado savanna community, Southeastern Brazil.

To consider at your Friday dinner tonight: Sex-biased diets affect the ecology of other species in the surroundings. Read more in the new early View paper “Antelope mating strategies facilitate invasion of grasslands by a woody weed” by Shivani Jadeja and colleagues. To get a good feeling of the antelope and the seeds that the males eat, read Shivani’s beautiful description of the wildlife reserve in western India, in her summary of the paper:


Mesquite (Prosopis juliflora) pods

In Velavadar National Park, a grassland wildlife reserve in western India, invasive mesquite trees (Prosopis juliflora) obstruct the horizon, where the land meets the sky. The dominant woody plant in the area, mesquite juts out as green crowns among the drying grasses that give the grassland a hue of yellow, red and olive streaks in the winter and summer. Velavadar is home to a large population of the threatened native antelope, blackbuck (Antilope cervicapra). Male blackbuck defend territories in open grasslands; these territories are either solitary or in clusters called leks. The classical lek in Velavadar, the size of a football field, may have more than ninety rutting males during peak mating season. During this time, the lek turns into a battle field where males perform strenuous displays and engage in fierce fights to defend their territories. Females visit the lek and seem to use a variety of information to choose a male to mate with. Males use urine and dung to create huge scent marks on their territories. These dung-piles can be seen as black dots from outer space (Look at blackbuck dung-piles on Google satellite images at 22° 2’54.82″N and 72° 1’20.78″E).


Fruit removal by male blackbuck (Antilope cervicapra) captured in a camera trap

3_Seed deposition through dung on a male mating territory- Inset- Large dung-pile on the classical lek

Seed deposition through dung on a male blackbuck mating territory. Inset: A large dung-pile on the classical lek


Presence of mesquite seeds in blackbuck dung

As blackbuck prefer open habitats, we predict that this concentrated seed dispersal by males will result in a positive feedback process where territories, which are typically in open grasslands, are modified into woodland patches, following which  males shift their territories to more open areas. We also predict that this male-aided conversion of grasslands to mesquite woodlands will negatively affect this open plains antelope species and cause shifts in mating system and social organization and a reduction in population size. Thus, here is one mechanism of spread of a woody invasive in grasslands, where one sex of a disperser, here male blackbuck, through its extreme mating behaviour, is planting seeds in new habitat, and perhaps negatively affecting its own lifestyle.


Seedling growing in a dung-pile on a blackbuck mating territory

Posted by: oikosasa | March 12, 2013

The little black dress of ecology

Taylor´s power law and bird populations are studied with in the new Early View paper “Interspecific differences in stochastic population dynamics explains variation in Taylor’s temporal power law”, by Marit Linnerud and her coworkers. Here’s Marit’s summary of the study:

Taylor’s power law – an oldie but goodie!

Taylor’s power law is like the little black dress of ecology, a general law that fits every species regardless of size or other personal characteristics.  According to the law the variance of population abundance in either time or space can be described by a function of the mean. A reasonable null expectation following from the definition of the variance is that as the abundance of a population increase by one unit on a logarithmic scale the variance is expected to increase by two logarithmic units, resulting in a slope of two. However, empirically the slope is often less than two, thus revealing some interesting ecological dynamics. Although the causal mechanism behind the law is not agreed upon, it seems likely that several factors are at play. A theoretical framework based on stochastic population dynamics provides testable predictions of what causes the deviations from the expected slope of two.

In our recent study we estimate the temporal mean-variance relationship for a large number of British bird populations. There were two significant challenges. Firstly, we could not ignore that sampling in itself could bias the estimates of the variance and secondly the estimated of variance increases with the number of years the population have been studied. Taking this into account we evaluated how the different deterministic and stochastic factors known to affect temporal population dynamic influenced the slope of the power law. It turns out that differences in demographic stochasticity among species were the main explanation of the variation in the slopes of Taylor’s power law.

Posted by: oikosasa | March 8, 2013

Cocktail mingle ecology

I would so much like to see someone using Hari Sridhar, Ferenc Jordán and Kartik Shankers paper “Species importance in a heterospecific foraging association network” as a basis for a study of humans on cocktail parties. Which small groups may be the core of highly important individuals (instead of species)? Is the same group of people important if they go to a party in another place? Or to a scientific conference in another research area? Or are humans not at all like birds?

Here is Hari’s background story to the study. The beautiful drawing is made by Rangu Narayan.

Chance and luck played a big part in the making of this paper. It was early 2008, and I had just begun my doctoral work on mixed-species bird flocks, when Ferenc visited my department. Ferenc specializes in using network approaches to tackle problems in ecology. In a talk during his visit, he mentioned that ‘network thinking’ was particularly useful in two ecological contexts: (1) to understand interactions among individuals in animal social groups (2) to understand interactions among species in communities, e.g. foodwebs. When we heard this, both Kartik (my PhD supervisor) and I immediately realized the value of network thinking in my doctoral work because mixed-species flocks fit both the contexts that Ferenc highlighted. Each mixed-species flock is a social group built on interactions among individuals of different species; but across multiple such flocks in an area, populations of species are linked in a community-level species interaction network. We spoke to Ferenc and he readily agreed to help us, since he too was keen on trying his hand at a new ecological system.  Given our different geographical locations (Ferenc was based in Trento, Italy, and Kartik and I in Bangalore, India), the plan was to work the collaboration entirely over email. But another lucky break meant that I could go to Ferenc’s institute in Italy to work on the project. My fieldwork was supported by a grant from the International Foundation for Science (IFS), of which a large portion remained unused till the end.  IFS allowed me to use this money to travel to Italy for two weeks in early 2012. Over endless cups of coffee and food at an Indian (!) restaurant in Trento, Ferenc and I built and analysed the flock networks for this paper.


 This collaboration had other useful spinoffs. Ferenc came back to India in 2012 to conduct a network analysis workshop as part of a student conservation conference in Bangalore that Kartik and I were involved in organizing. Kartik and Ferenc are also putting together a special issue on ecological networks for a conservation magazine called Current Conservation, which will include a non-technical piece based on this Oikos paper.

Posted by: oikosasa | March 7, 2013

Theoretical weed ecology

Do you like trying new food items? I do. And many herbivore insects seem to do so as well. Invading alien species, yummy yummy! How these interactions affect the ecology of the invaders is studied by Matthew L. Forrister and Joseph S. Wilson in “The population ecology of novel plant–herbivore interactions”. Here’s their background to the study:

Everyone knows that weeds are everywhere these days, and most ecologists know that native insects often like to eat exotic plants.  That dynamic (native herbivores utilizing novel hosts) has been very productive for evolutionary biologists (think about the apple maggot fly on apple or the soapberry bug on goldenrain trees), and has become increasingly useful for ecologists who realize that we can watch novel interactions and communities assemble before our eyes.


The ubiquity of interactions between native herbivores and novel plants has led to an imbalance in the ratio of empirical to theoretical work.  Moreover, some of the relevant theoretical work (for example on the evolution of niche width) is not always accessible to the average field biologist observing caterpillars eating weeds.  Our motivation in writing this paper was to provide an easily accessible conceptual framework that might serve to organize and focus experimental approaches.  For example, studies are often reported in which the “preference-performance” relationship is examined using native insects reared on native and exotic hosts.  We believe that the focus on that particular relationship demonstrates a certain inertia in the literature that should be overcome, because (for one thing) a rather definitive meta-analysis of that issue has been recently published (Gripenberg et al. 2010 Ecology Letters 13:383-393), and moreover there are many other facets of insect life history that need to be studied, such as interactions with natural enemies, indirect interactions with other herbivores or behavioral factors that affect realized fecundity.

In addition to making the rather fundamental point that our studies need to go beyond the performance of juvenile herbivores and the preference of ovipositing females, we offer some hypotheses to challenge assumptions and spur future work.  We present our hypotheses in qualitative, graphical format in the spirit of the late Robert MacArthur.  Some quantitatively-sophisticated readers might find this approach simplistic, but we hope that other readers will find it useful.  For example, we ask about the shape of the relationship between dispersal ability, population growth rate on a novel host, and the rate at which a new host is utilized.  Also in the spirit of MacArthur, we hope that other researchers will be inspired to propose alternative hypotheses, which is something that we believe the graphical (as opposed to verbal) format encourages.

Posted by: oikosasa | March 5, 2013

Can we trust field-guides in ecological studies?

How consistent are field-guides and atlases? Enough to be used as sources in ecological research studies? Jay Fitzsimmons has checked and has the answer! Find out in his new Early View paper “How consistent are trait data between sources? A quantitative assessment”. Below he tells us what made him conduct the study:

Compare all the sources meme

I compared several field guides and atlases to see whether they were consistent in what they said about species’ traits.  The proximate reason why I did this research is that, given the popularity of trait-based research, I wanted to determine how consistent trait data were among authoritative sources.  The ultimate reason why I did this research is that I’m a paranoid city slicker who worries over how little I know about my study species.

Trait-based ecology is increasingly popular, with researchers evaluating whether species’ traits are related to a variety of ecological factors (e.g., extinction risk, invasiveness).  In my PhD I did such an analysis myself, evaluating the relationship between butterfly species’ traits and their rates of northward range shift in Canada over the 1900s (not yet published – it’s only been two weeks since my PhD ended so give me a break).  The advice given to me on how to obtain species’ trait data was “just use an atlas or a field guide.”  This is when my paranoia alarm started ringing.  Which atlas or field guide should I use?  Do they all say the same thing?

 While I love and respect natural history (I volunteer as Journal Manager for The Canadian Field-Naturalist –, I am not a great naturalist myself.  I cannot even identify most of Canada’s butterflies, never mind critically evaluate the accuracy of their trait data.  This is a serious problem for macroecology that isn’t given the critical attention it deserves: researchers using fancy models and elaborate analyses can miss critical issues if they don’t know the natural history of their study species.  Non-naturalist macroecologists can miss interesting results that merit follow-up, or wonky results that could indicate coding errors.

 So which source should a paranoid, butterfly-ignorant macroecologist use?  All the sources of course!  Ok, not all the sources (not by a long shot), but I used five authoritative sources authored by recognized experts.  I entered data from each source for 22 traits for 263 Canadian butterfly species.  I compared trait data for species across sources: do different sources say the same things about species?  I found some traits to be very consistent across sources, and others worryingly inconsistent.  In general it seems that subjective traits (e.g., habitat association) were less consistent than more clearly-defined traits (e.g., wingspan, over-winter stage).  This suggests results from single-source trait studies may depend in part on which source was used for trait data.

It was a pleasure to do this work, and to vindicate my paranoia (I can put the tinfoil hat away for another day).  I hope others do similar comparisons of field guides and atlases for other taxa and regions to reveal how general my findings are, and what effect such inconsistency has on trait-based research results.

How do animals decide how to forage? In the new Early View paper “How a simple adaptive foraging strategy can lead to emergent home ranges and increased food intake” Jacob Nabe-Nielsen and colleagues demonstrate that it only requires a few simple behavioural rules to produce most of the complex movement patterns observed for harbour porpoises.

What is it that makes an animal stay within more or less the same area for weeks or months before eventually moving to a new place? Surely it must have been feeding in the area, but how does it decide when it is time to leave? One of the central questions in behavioural ecology is whether animals have evolved many different kinds of behaviour, where each behavioural response is fine-tuned to a particular condition that the animals encounter in nature, or if a few simple mechanisms are sufficient to enable them to respond optimally in a wide range of conditions.

Porpoise in a pound net

The simulated harbour porpoise movements closely corresponded to those of satellite-tracked animals.

Porpoise release after tagging

The harbour porpoise (Phocoena phocoena) is an example of an animal species that displays very complex movement patterns. Porpoises often stay within relatively well-defined areas, or home ranges, where they presumably prey on various species of small fish before moving to new areas. In order to investigate whether a few different cognitive mechanisms could be sufficient to generate this complex behaviour, we developed a simulation model that included only two different kinds of behaviour. In the model the food was distributed in minute, scattered patches. Animals that had recently found plenty of food moved at random, much like cows that walk at their own pace in a field with lots of fresh green grass. Animals that had not been able to find food for some time became increasingly attracted to the patches where they had found food in the past. We let the animals’ ability to find their way back to previously visited food patches be governed by a spatial memory. It turned out that the combination of these two kinds of behaviour enabled home ranges to emerge, and when the animals’ memory about previously visited foraging sites decayed at a particular rate the model was able to produce movement patterns that closely resembled those observed for satellite-tracked porpoises in Danish waters. The right balance between the two kinds of behaviour also allowed animals to maximise their food intake. This suggests that it could be selectively advantageous for animals to base their decision on how to forage on a few, simple behavioural mechanisms.

Posted by: oikosasa | March 1, 2013

Plagiarism in Oikos?

We now check all submitted manuscripts for possible plagiarism using iThenticate.This means that all manuscripts are compared to more than 32 billion webpages, more than 34 million scholarly content items and more than 91 million news pages, books and magazines (and yes, these numbers are “plagiated” from iThenticate’s webpage…).

How similar are manuscripts generally to already published stuff? Most manuscripts show between 5 and 15% similarity.

And where is the limit for plagiarism? When a paper show more than 25-30% similarity with other published material, we do a thorough check for the similarities.

Reference lists, protocols in Methods and author adresslists may generate high similarities that are not really plagiarism. When high similarities are found in Results and Discussion, we act.

So it’s no use trying the copy and paste method for Oikos manuscripts…

Posted by: oikosasa | February 26, 2013

Top of the Pops

One of the most cited papers in Oikos, during 2011 (published 2009 and 2010) is “New perspectives for estimating body condition from mass/length data: the scaled mass index as an alternative method“, by J Peig and AJ Green.

Here, Jordi Peig gives a short summary of the paper and an explanation to it’s impact:

Jordi and Andy

Body condition (physical or nutritional status) is a widespread concept in the ecological literature. Although usually poorly defined, it encapsulates the animal’s health, quality and vigour, and hence its biological fitness. Scientists have used different approaches to estimate BC, but those based on morphometry and particularly on mass-length relationships have been adopted for routine use due to the ease of application and their ‘a priori’ conceptual simplicity. Briefly, morphometric indices attempt to quantify how heavy is an organism for a given body size, because the extra mass indicates more fat and protein reserves to overcome periods of food scarcity or high energy demand in general. However, larger animals will be inherently heavier, and vice versa, so the standardization of body size is the central challenge that underlies all morphometric methods, and is the subject of our paper. Many mathematical formulas and statistical methods have been proposed to standardise body size, yet there is still much debate among scientists as to the most suitable method.

The work published in Oikos has been popular partly because so many studies included attempts to establish the influence of body condition in population ecology. The idea of the paper was born in 2006 when distinct BC indices reported in the literature yielded opposite results when applied to my own data on small mammals. I found that those contradictory results were each scientifically plausible and arguable from an ecological viewpoint, hence the need to rethink the nature of these methods. After reading in and around the subject, including biostatistics, theoretical biology and epidemiology, I conceived the Scaled mass index. Because of the intrinsic tendency within sciences towards specialization, different disciplines have promoted and advocated their own methods (including the Body Mass Index used in medicine), and I searched for a common, unifying approach. With this complexity in mind, and the difficulty of publishing in this area for a PhD student (introducing alternative methods inevitably meets some scepticism and resistance) led me to seek collaboration with my co-author Andy Green, who had previously published in this field. From our first contact by email Andy was enthusiastic, and made substantial improvements to the manuscript. My original draft was prohibitively long for modern journals, and part of it went into a sister paper in Functional Ecology in 2010.

In the Oikos paper we attempt to explain the complexity of the BC issue from the fundamental viewpoint of allometric growth, and develop the Scaled Mass Index from that perspective. Amongst the papers that have cited our work, there are good independent examples of how our index outperforms previous methods. We can only hope that our future contributions on this topic become as successful as the Oikos’ paper.


Posted by: oikosasa | February 22, 2013

Mites hitch-hiking with bugs

Thumb’s out when the mite Spadiseius calyptrogynae needs to move to a new host plant. It can’t get their on it’s own, so it simply hitchhikes on bees, bats or beetles. Emanuel H. Fronhofer and co-workes have studied this in the new Early View paper “Picky hitch-hikers: vector choice leads to directed dispersal and fat-tailed kernels in a passively dispersing mite“. Here is Emanuel’s summary of the exciting study:

Tropical species diversity can be so high that while walking through a lowland rainforest it may be difficult to see two individuals of the same tree species. This phenomenon has fascinated generations of naturalists, but at the same time such high diversity represents a considerable challenge for any organism that, because of its biology, has to find another tree of a certain species to feed on, for example. How do specialized mutualists, predators or parasites manage to find their host(s)? This problem is especially relevant and critical for a lot of small, non-mobile species that occupy ephemeral habitats, such as small ponds, dung or, as in this study, flowers.

In this context, we have studied the dispersal strategies of a neotropical phoretic flower mite, that uses a number of different animal vectors – bats, beetles and bees – in order to hitch-hike from one host plant to the next. These mites (Spadiseius calyptrogynae) are specialized to their host plant, an understorey palm (Calyptrogyne ghiesbreghtiana), while the flower visitors and potential dispersal vectors are generalists.


The long distance disperser (Chasmodia collaris) on a male inflorescence of the palm Calyptrogyne ghiesbreghtiana (left). The detail (right) shows the phoretic mites (Spadiseius calyptrogynae) shortly after boarding their dispersal vector. Photo: E.A. Fronhofer.

Using a dual approach that combines field observations with experiments and individual-based modelling we find that our study species shows a highly developed capacity to discriminate between potential dispersal vectors based on chemical cues. These mites choose their dispersal vectors in order to optimize their dispersal kernel, i.e. the distribution of dispersal distances. The evolutionarily stable dispersal kernel is a mixed kernel resulting from short distance dispersal with bees (Trigona fulviventris) and rare long distance dispersal events with beetles (Chasmodia collaris). This results in a fat-tailed distribution of dispersal distances and additionally guarantees directed dispersal towards especially suitable habitat, as the short distance dispersers prefer young over old flowers.

Besides being an example of information use for making dispersal decisions, we show how passive dispersers may realize directed and long distance dispersal. Furthermore, our study highlights the benefits of combining field work and individual-based modelling or theoretical approaches in general.


Posted by: oikosasa | February 20, 2013

New populatin metrics for top-down-bottom up

Here is an interesting essay about measuring top-down-bottom-up effects, written by Leonard Polishchuk. He is also the first author of the Early View paper “How to measure top–down vs bottom–up effects: a new population metric and its calibration on Daphnia“, on which the essay is based.

Arguably, one of the saddest fallacies in ecology is the concept that «Everything is connected to everything else» (known as the first Barry Commoner law of ecology). The key assumption underlying this concept is that all interactions within the system are equally strong. Let’s examine which kind of science this assumption implies. Even in a modest system of 10 species the number of pair interactions between species amounts to 55 (including the effect of a species on itself), and to 5050 for a system of 100 species, leaving aside interactions with the abiotic environment. Such a large number is too big to study the interactions on a one-by-one basis, but probably too small to completely ignore their individuality. The latter is possible if the number of interacting entities is on the order of 1023, the Avogadro constant, but this will lead us to the realm of statistical physics rather than ecology. The Commoner law, if correct, would make our attempts to understand Nature almost hopeless, and turn ecology into hardly more than a casebook of idiosyncratic examples. Or, following Ernest Rutherford’s famous dichotomy, ecology would have been close to stamp collecting rather than hard science. (Rutherford actually said “physics” and was basically right, because physics is a role model for genuine science. But we do not think that “physics envy” can really motivate the ecologist.)


The picture is not all gloom, however. Rather than falling into despondency, one could quantify species interactions in order to see whether they are of the same strength or not. The actual problem, as it often happens, is therefore an operational one; it is about how to measure the things of interest. Let us focus our attention on trophic interactions, that is, on bottom-up and top-down effects. One way to assess them dates back to Justus von Liebig and consists of addition of biological nutrients to see which of them elicit a strong response from the pot plant, in terms of its growth, or from the planktonic algae in a water sample, in terms of primary production. These simple experiments, which in the era of ANOVA are called factorial-design experiments, immediately disprove the Commoner law. Liebig’s law of the minimum states that there is a single factor that produces the biggest response in a given species or a set of species with similar requirements, and thus affects them most strongly. Hence, not only the interactions are different in their strength but, under any given circumstances, there is only one that is most important. Clearly, the Liebig law makes a contrast with the Commoner law.

While the factorial-design experiment is a powerful and efficient tool to reduce the number of significant interactions and detect the strongest one, it has its shortcomings. The imposed shifts in food and/or predator abundance, while not completely arbitrary, may not reflect the current situation in the system. Often, for example, one of the treatments completely excludes predators, despite their presence in the environment. In his 2001 review, Mark Hunter sarcastically notes that if we were to completely exclude food, this would have inevitably revealed an “obvious and dramatic bottom-up effect”. Of course, nobody would act that way in regard to food but this reductio-ad-absurdum example shows a general problem: the manipulative (addition / removal) approach does take into account the actual (rather than imposed) dynamics observed in the system. The dynamics is a fundamental feature of natural systems (Pimm 1991), implying that one driving factor, e.g. food, may be quickly replaced by another, e.g. predation, in the course of time and space. The factorial-design experiment is not tuned to track these changes while a truly dynamic approach might be able to make it.


These considerations naturally bring us to the field of population dynamics. In the paper, we have focused on zooplankton, in particular Daphnia, a well-known model organism in ecology (Lampert 2011, see Figure), though we do believe that our approach is a general one and may not be limited to zooplankton. The population characteristic we are dealing with is birth rate. In part, this is because planktonologists can take advantage of the Edmondson-Paloheimo model for birth rate. Interestingly, birth rate as a response variable is somewhat similar to growth or production rates often taken as response variable in manipulation experiments, but our use of it is different. The Edmondson-Paloheimo model, being slightly modified (Polishchuk 1995), relates birth rate to fecundity and proportion of adults in the population. Fecundity is closely associated with food conditions and proportion of adults with size-selective predation, the latter being common in zooplankton. Thus, birth rate depends on both bottom-up and top-down effects, which is another reason why it is used here. To quantify the role of fecundity and hence bottom-up effects and that of proportion of adults and hence top-down effects in birth rate dynamics, we employ a mathematical approach called contribution analysis (Caswell 1989, Polishchuk 1995, 1999, Polishchuk and Vijverberg 2005, Hairston et al. 2005, Ellner et al. 2011). This provides us with the ratio of contributions of changes in the proportion of adults and fecundity to birth rate change taken as a measure of the relative strength of top-down vs. bottom-up effects.

We view the ratio of contributions as a kind of measuring instrument, something like a thermometer. The comparison of the ecological instrument to the physical one is, of course, a metaphor – primarily because ecological variables do not obey simple and general quantitative relations such as those used to construct physical instruments; an example is the relation describing the thermal expansion of the physical body, which underlies the functioning of the thermometer. But it is a useful metaphor, for it leads to the next task: calibrating the ratio of contributions as a tool to measure the strength of top-down vs. bottom-up effects. This calibration is based on microcosm and computer experiments, and constitutes a major part of the paper. The main experimental result is that the ratio of contributions allows one to distinguish a strong top-down effect from a strong bottom-up effect.

In the end, we would like to emphasize some points not mentioned in the paper. First, while our approach focuses on population dynamics and, as such, is intended to avoid inappropriate averaging (used, though implicitly, in manipulative experiments), some time-averaging seems necessary. The ratio of contributions is found to be sufficiently robust only when applied to a set of successive sampling intervals rather than an individual interval. (This set covers the second part of the experiments where top-down and bottom-up effects appeared in full strength; see Online Appendix 3 of the paper.) In our experiments, this set was identified by means of ANOVA, the procedure that will not apply to field populations due to lack of “replicate populations”. Hence, we need to understand how to recognize, in natural populations, a set of intervals over which the ratio of contributions remains roughly constant. This will open the way to the use of this approach for natural Daphnia (and other zooplankton) populations.

Second, the Edmondson-Paloheimo model, when appropriately modified, has the potential to estimate birth rate in animals other than Daphnia, such as mammals. If applied to a wider range of organisms, this approach may be a useful supplement to conventional Liebig-style factorial-design experiments.

Posted by: oikosasa | February 18, 2013

Hiding in the litter from the beasty ants

In the new Early View paper “Non-trophic effects of litter reduce ant predation and determine caterpillar survival and distribution”, Richard Karban and co-workers have studied the importance of litter for caterpillars hiding from ants in a hetergenous landscape. Here is Richard’s lay summery of the paper:


It is well established that trophic interactions can influence the spatial distribution and abundance of organisms.  What is less well understood is how these interactions vary across space.  In this study, we conducted several observational surveys and manipulative field experiments to examine the role of predators as drivers of caterpillar abundance and distribution across a heterogeneous landscape composed of three predominant habitat types, marsh, coastal grassland, and dune.  Unexpectedly, ants were found to readily prey upon early instar caterpillars.  The intensity of predation varied across habitat types such that caterpillars in marsh habitat had a higher probability of survival than those in drier, upland habitat. Marsh habitat in our study system is characterized by think leaf litter, while less leaf litter is associated with drier habitat.  We hypothesized that habitat substrate complexity may moderate caterpillar predation by ants. This hypothesis was supported by two findings: ant recruitment to baits decreased with litter depth and litter protected caterpillars when ants were present but not when ants were experimentally excluded. Our results show that litter confers a survival advantage to caterpillars by providing habitat, a non-trophic mechanism. In contrast to trophic effects, the importance of spatiotemporal variation of non-trophic effects in mediating species interactions has been underappreciated by many ecologists.


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