Oikos Blog

Isn’t it just amazing how well adapted the tiny parasitic wasps are? Parasitoids want to lay their eggs in good, yummy caterpillars. Yummy caterpillars are those feeding on high quality plants. Quality of plants is partly determined by if their roots have been eaten by below ground herbivores. Plants smell differently above ground, depending on if their roots have been eaten or not. These odour variations are learned by the parasitic wasps when identifying the high quality hosts.

These results are presented in the new Early View paper “Effect of belowground herbivory on parasitoid associative learning of plant odours” by Marjolein Kruidhof and her co-workers. Here’s Marjolein’s own summary:

Only experienced parasitic wasps adapt their preference for plant odours in the presence of root feeders

Although hidden in the soil, insects that feed on plant roots often do not go unnoticed by insects living aboveground. Upon root feeding, the odour the plant emits into the air changes. Tiny parasitic wasps, which lay their eggs inside the body of host caterpillars that feed on the plant leaves, use these plant odours to locate their hosts. Researchers from the Netherlands Institute of Ecology (NIOO-KNAW) in the Netherlands tested whether two closely-related parasitic wasp species, Cotesia glomerata and C. rubecula, expressed a preference for plants with or without Delia radicum root feeders. As inexperienced wasps of both species did not respond to the presence of root feeders, they continued to investigate whether the parasitic wasps could develop a preference after gaining experience when parasitizing caterpillars on root-infested or root-uninfested plants. Indeed, both wasp species adapted their preference for plant odours to the presence of root feeders, but did so in an opposite direction.  While C. glomerata learned to prefer the odour of plants with intact roots, C. rubecula learned to prefer the odour of root-infested plants. These findings stress the importance of not only assessing the influence of root herbivores on the responses of inexperienced parasitic wasps, but of also taking learned responses into account. In a publication that will soon appear in Oikos the authors discuss the possible reasons why these two parasitic wasp species respond so differently towards the presence of root feeders.

What are the chances that the reefs recover? And how likely is it that they just turn into seeweed-dominated ecosystems instead?  Important issues that Peter Mumby and his colleagues have studied and modelled in the new Early View paper “Evidence for and against the existence of alternate attractors on coral reefs”.

Here’s Peter’s summary of the study:

In the new Early View paper “Predator-mediated interactions between preferred, alternative and incidental prey in the arctic tundra”, Laura McKinnon and her colleagues used the Arctic Tundra in Canada as a natural laboratory to study predator-prey interactions.

Here is Laura’s short version of the paper:

Predators can have direct impacts on prey populations by decreasing survival and fecundity, and in turn, prey populations can also drive predator densities.  These interactions between predator and prey can often lead to coupled cycles in population abundance, many studies of which have become classic textbook examples in ecology.  More recently, these models have been expanded to incorporate multiple prey species and even multiple trophic levels in order to have a better understanding of the causes and consequences of predator prey interactions in more complex realistic environments.  However, testing these models in complex ecosystems can become rather cumbersome due the sheer number of interactions between species.  Luckily, there are some terrestrial ecosystems, such as the Arctic tundra which provide less complex natural laboratories in which to study trophic interactions between predators and multiple prey items.   In our recent study, we took advantage of this natural laboratory to study indirect interactions between preferred, alternative and incidental prey.

In the arctic tundra, numerical and functional responses of predators to preferred prey (lemmings) affect the predation pressure on alternative prey (goose eggs) and predators aggregate in areas of high alternative prey density.  Therefore, we hypothesized that predation risk on incidental prey (shorebird eggs) would increase in patches of high goose nest density when lemmings were scarce.  By measuring predation risk on artificial shorebird nests in quadrats varying in goose nest density on Bylot Island (Nunavut, Canada) across 3 summers with variable lemming abundance, and monitoring quadrats for predator activity, we provide evidence that the abundance of preferred prey influences the indirect relationship between alternative and incidental prey.  Predation risk on artificial shorebird nests increased in the presence of increasing goose nest densities, especially at low lemming abundance, as predicted.  In addition to supporting our incidental prey hypothesis which suggests that when preferred prey decrease in abundance, short-term apparent competition via aggregative response can occur between alternative and incidental prey, these results also provoke interesting applied questions regarding the potential effects of increasing goose densities on incidental prey such as shorebirds.

Seed diseprsal by animals is an important ecological service. How selective or general the animals are in their choice of fruits to eat might have a huge effect on dispersal of the plants. Read more in the new Early View paper “Individual variation in resource use by opossums leading to nested fruit consumption” by Mauricio Cantor et al.

Here is the authors’ own summary of the paper:

Seed dispersal by fruit-eating vertebrates is an important ecological service that has consequences for the plant community and regeneration process. Despite recent findings on the ecological relevance of within population diet variation far less attention has been devoted to the role diet variation for ecological services, such as seed dispersal. In this paper we unravel fruit consumption patterns by the white-eared opossum (Didelphis albiventris), a South American didelphid, which is regarded as an important seed disperser commonly found in disturbed environments, where vegetal regeneration is especially required.

We detected fruit consumption patterns suggesting these opossums may differ in their degree of fruit selectivity what may result in heterogeneity in seed dispersal efficiency within the population. In this sense, the actual result of the seed dispersal provided by these animals probably differs from what one would expect from the average behavior of the population. The result of such heterogeneity would probably be dependent on the proportion of opportunistic and selective individuals in the population. This frequency-dependent seed dispersal may have implications to both plant individuals and species, affecting plant performance and the local plant community composition.

Invasive species may actually increase resistance to climate changes. Celia Olabarria and co-workers studies this interaction in marine macroalgal assemblages.  Now on early View: Response of macroalgal assemblages from rockpools to climate change: effects of persistent increase in temperature and CO₂

Here is a short summary by the authors:

Climate change is one of the greatest threat  that marine systems are facing. Changes in ocean temperature, biogeochemistry, sea level, UV radiation, and circulation patterns have been identified over the last few decades. Specifically, warmer and more acidic oceanic water (due to the increase of CO₂ in the atmosphere and oceans) are of great concern to marine biologists. Non-indigenous species are also impacting marine communities around the world at an unprecedented rate. These species are often ecosystem engineers (e.g. brown canopy algae) that can replace native species and their functional role in the ecosystem, or modify habitat characteristics and food sources for consumers. We do not have information about how invaded communities will respond to climate change compared to non-invaded communities.

Marine macroalgae that dominate the rocky intertidal in most oceans, and in temperate and Polar regions cover rock surfaces in the shallow subtidal, make a substantial contribution to marine primary production (10%) and describe important ecological functions. They may be also actively involved in lowering global warming and climate change. Research about effects of different climate change scenarios on macroalgae has found quite variable and species-specific responses. Until now, most research has focused on the effects of climate change on single macroalgae species, rather than on whole communities. While this approach is useful for understanding species-specific mechanisms behind the effects of environmental changes, it ignores species interactions which may buffer or amplify individual responses thereby altering predicted assemblage-level responses.

Macroalgal assemblages from rock pools are interesting model systems to study climate-driven changes because they are composed of different morpho-functional groups of varying diversity and identity of species. Despite coping with daily and seasonal variations in pH and temperature, their response to more persistent changes are unknown. We were able to manipulate temperature and CO₂ concentration in mesocosms to evaluate how these to climate-change factors affected several ecosystem functioning variables at both individual and assemblage level. For that, we used synthetic macroalgal assemblages of varying diversity and identity of species resembling those characteristic of rock pools.

Results revealed that the increase in temperature and CO₂ concentration may interact and affect the functioning of coastal macroalgal assemblages, with effects largely dependent on species composition of assemblages. Although the effects of assemblage richness were mostly negligible, significant differences were found between the response of native and invaded assemblages. Data suggested that  invaded assemblages might be more resistant in the predicted future scenario of climate change. This paper emphasises the importance of using multiple stressors-study approaches at community level to get better predictions of climate change impacts on ecosystem functioning.

Photo: F. Arenas and M. Matias

Protein or fat in food – which is best? Well, if you’re a female preying mantid, you should definitely go for the high-protein diet! Females on high-lipid diet attract much fewer males than females on high-protein diet. These results are presented in the new Early View paper “Macronutrient intake affects reproduction of a predatory insect” by Katherine L. Barry and Shawn M. Wilder.

Here is a short summary by Katherine:

We tested how diet affected the reproductive success of female praying mantids by feeding them live locusts that were injected with solutions of lipid or protein.  Not too surprisingly, females fed high-lipid locusts gained more fat and produced about half as many eggs as females fed high-protein locusts. 

We also tested female attractiveness by placing females in small mesh cages (that excluded visual cues) within large enclosures, and allowing males to choose between females from the different feeding treatments.  Usually females with more eggs are more attractive than females with less eggs and, in our study, the high-protein females attracted more males (56 males) than the high-lipid females (1 male).  However, the effect was much more extreme than we predicted.  In previous studies, females were fed a standard diet of crickets, and individuals with as few as one egg were able to attract up to three males.  But in our study, females on the high-lipid diet had over 20 eggs on average but only one female attracted one male.  Hence, diet quality seems to have a large effect on the quantity or quality of pheromone produced by females.  It would be interesting to test how diet mediates pheromone production in praying mantids and if similar effects occur in other species of arthropods.

You can now find a list of the most cited Oikos papers 2011, that were published in 2009 and 2010, on our webpage.

On top of the list,  is “A consumer’s guide to nestedness analysis” by Werner Ulrich, Mário Almeida-Neto and Nicholas J. Gotelli.

Here is a short description by Werner Ulrich, on what it’s all about:

Ecologists look for patterns in nature. The nested pattern – in which the composition of small assemblages is a nested subset of larger ones - is one that received a lot of attention, both because it is so simple and because it is so common. In biogeography, if sites are ordered by area or along an environmental gradient, a nested pattern can be interpreted as an orderly loss of species along the gradient. This is the most common interpretation of nestedness. It was popularized in the 1980s by Bruce Patterson and the late Wirt Atmar, who introduced a nestedness temperature calculator, compiled a large set of ecological presence-absence matrices from the published literature, and detected nestedness in most of them. Since then, much research has been devoted to articulating alternative mechanisms for nestedness, and developing appropriate metrics and null models for testing the pattern. Nestedness has also been used in food web or species interaction analysis, population genetics, and even molecular biology. However, the nestedness tale is also a story of failure and a warning on the challenges of statistical pattern analysis in ecology. Many studies have unfortunately used ad hoc measures of the degree of nestedness, inappropriate statistical benchmarks, and questionable ecological arguments. That was the point where we (Nick, Mario, and I) stepped in. The origin of our “consumer’s guide” paper was from an idea of Mario’s, who noticed that the quantification of a nested pattern went into a wrong direction. He asked me to take part in the development of a new metric, and the resulting Oikos paper was a success. We then tried to give guidelines for proper pattern identification and testing. During the writing, we noticed how many snags even a simple pattern like the nested one provides for researchers. Apparently, many other scientists shared our views. Our impression is that the quality of nestedness research has improved during the last few years, and we hope that our review has contributed to that trend.

During the work on nestedness, we started developing new metrics to quantify observed patterns and expanded the framework for proper statistical testing. Two new Oikos papers by Nick and me on statistical challenges and on pattern detection in ecology are the fruits of these efforts. We can only hope they will become as popular as the “consumer’s guide” to nestedness.’

So those small small seeds produced by plants have actually big effects on plant demography. Read more in the Early View paper “Non-native conditions favor non-native populations of invasive plant: demographic consequences of seed size variation?” by José L. Hierro et al. 

Or be quicly updated by Josés own short summary:

We conducted a reciprocal common garden in part of the native (southwestern Turkey) and introduced (central Argentina) range of a globally distributed plant invader, Centaurea solstitialis (yellow starthistle, Asteraceae) to explore the idea that the demographic success of the species in Argentina relates to differences between native and introduced populations.   Unusual among common gardens, our experimental design included seed additions to explicitly evaluate population level responses.  We found that seed mass was two times larger for Argentinean than Turkish populations.  Similarly, plant establishment at the end of the experiment was greater for Argentinean than Turkish populations, but only in the common garden in Argentina.  In Turkey, we detected no differences in plant establishment between population origins.  Our results suggest that increased seed size in Argentinean populations may have demographic consequences under central Argentina conditions that can contribute to the invasive success of C. solstitialis.  Our study offers the most complete evaluation to date to the idea that variation in seed size can contribute to differences in plant density between native and non-native distributions of invasive plant species.

Field site in Turkey (native)

Field site in Argentina (introduced)

When I did an undergraduate project at Silwood Park, my supervisor, Hefin Jones used to say that ecological research is about 10 % inspiration and 90% transpiration. And this is exactly what Winfried Voigt report about in his story about his and his colleagues Early View paper “Bottom–up and top–down forces structuring consumer communities in an experimental grassland” (Rzanny et al.). He story also shows what might be the outcome of large collaborative projects.

Gathering up sufficient and useful data for answering questions concerning entire communities is always a strenuous and costly job. It is actually only feasible when working in cooperation with a large team. We were lucky to be involved in an appropriately large team, the Jena Experiment, a controlled biodiversity experiment [http://www.ecology.uni-jena.de/en/Jena_Experiment_Inst_of_Ecology.html]. The dimensions (10 ha, 80 plots each 20×20 m with a set plant species diversity of 1, 2, 4, 8, 16 and 60 as well as 1,2,3 or 4 functional plant groups, and numerous smaller plots) are unique and  turned out to be the right platform for asking “bigger” questions about structure and function in grassland communities. A lot of periodic work, in particular weeding, was done by a capable maintenance staff (5 professional gardeners and numerous student assistants) so that the only thing left to do was to collect our own data. Nevertheless, for our closer small team (with some support  of a few student assistants) even that was quite a strenuous job but all the effort and suffering (not to say blood, sweat and tears) are not  always obvious if one looks at the end result on just a few hundred Kbyte of data we hold in an excel file. We collected arthropods 5 times, from May to October in 2005, on 5 quadrats randomly placed within the core area of 50 big plots (16 monocultures, 16 four-species, 14 sixteen-species and four 60-species mixtures) using suction samplers combined with biocenometers (see photograph) as well as using pitfall traps. All in all, we successfuly accrued 322 arthropod species/taxa with 81658 individuals that we could exploit in the end.

Identifying the key factors for structuring ecological communities is at the heart of ecological research. Most studies dealing with this question on community level rely on lumped, aggregated variables such as summed species abundance, biomass or diversity measures or they confine to a small part of species usually one or a few taxa.

We already developed a different approach 10 years ago by assigning all species to functional groups representing approximately the entire community. Because we hold all functional groups as matrices containing abundances of their members (species), we acquire a sufficient simplification, while retaining full species information. As we see ecological communities as a system of interdependent functional groups, we performed an exploratory multivariate analysis, explicitly addressing species composition of functional groups. We used species resolved plant biomass and arthropod abundance data from the Jena Experiment to estimate the dependencies among plant – and consumer functional groups, thereby accounting for spatial effects and differences in soil conditions.

Using a set of five groups of biotic and abiotic predictor variables (Plants, Herbivores/Detritivores, Carnivores, Soil, and Spatial patterns), we aimed to determine the independent and shared fractions of variation explained by these variables in the composition of all consumer functional groups. Depending on the trophic level of the predictor variables, we quantified the relative roles of top-down and bottom-up effects.

It turned out that legume composition explaines the highest fraction of variation in virtually all consumer functional groups, indicating that legumes play a key role in controlling multiple ecosystem processes. Both plant species richness and plant functional richness show significant effects on (nearly) all functional groups, however, the fraction of variation explained is always exceeded by the fraction explained by plant community biomass. Carnivore composition explain significant fractions of variation in many functional groups, the same applies for the soil and space variables. Consequently, we conclude that bottom-up effects seem to play the most important role in structuring the consumer communities in our experimental system, but at the same time top-down effects are still important for the majority of arthropod functional groups.

Sometimes it’s worth bringing good old science back into the light. Hideyuki Doi and Terutaka Mori were inspired by two papers from 1932 and 1953 about species abundance distirbution and brought them into modern days’ science. Read the paper “The discovery of species–abundance distribution in an ecological community” on Early View. Here’s the author’s own background story:

Species–abundance distribution (SAD), representing relative species abundance, is one of the most basic descriptions of an ecological community. The description can represent more detailed attributes of the community than species richness. Universal observations that few species in a community are dominant, but that many more species are rare, can be neatly encapsulated in a SAD, but not represented by species richness.

Prof. Isao Motomura (1904–1981, photo) first found a SAD pattern for some animal communities and then published a notable paper in 1932. Motomura (1932) described SAD in the following way: ‘In a community, there are generally many more species with relatively low abundances. When the species found within a quadrat are ranked according to abundance (i.e. the order of dominance in the community), a definite graphic pattern is observed between the rank and abundance of species’. He found that a straight line is produced when logarithm of abundance is plotted against rank, and then fitted observed SAD to “geometric series”. Motomura’s study is the first discovery of a SAD pattern, but has often been overlooked or incorrectly cited, probably due to being published in Japanese.

In this article, we in-deep introduce the works of Motomura and the subsequent research history of SAD. Specifically, we also introduce the work of Numata et al., another Japanese paper, which provided the biological explanation for Motomura’s model of SAD. Numata et al. (1953) showed that Motomura’s model (i.e. geometric series) is explained by supposing that species occupy the available area according to the rank of a set of ability for individual and species survival (i.e. reproduction, competition, etc.). Therefore, they provided biological explanations with a deductive approach for Motomura’s model in which an inductive statistical approach was employed. We believe that the field of SAD is increasing in importance and activity, because SAD has proven to be one of the most important fundamental tools in community ecology and management. Motomura (1932) paper also includes an important suggestion for ecologists: ‘In a natural ecosystem, it is very unusual to find such geometric series for the abundances of species coexisting in a habitat’. The finding of such a surprising pattern in ecological communities therefore represents a frontier of ecological research. Our motivation for finding a new general rule in ecology is highly recommended.

Root competition appears to effect sex allocation in plants. Åsa Lankinen and her colleagues have studied this in the Early View paper “Allocation to pollen competitive ability versus seed production in Viola tricolor as an effect of plant size, soil nutrients and presence of a root competitor”. Here is a short summary by Åsa:

Even though plants lack brains, there is clear evidence that they can perceive and respond to their neighbours. For example, in some species plants can sense airborne chemicals transmitted from the leaves of another plant attacked by herbivorous insects, acting as a cue to start the induced defence system. Another example of plant communication is the possibility to detect the presence of self vs. non-self roots in the soil. Presence of unrelated root neighbours can even cause plants to allocate relatively more resources to their roots than to their shoots, thereby allowing more effective root-uptake when competitors are present. But can plants also use these kinds of cues to optimize their mating success, such as altering relative allocation to male versus female function in hermaphroditic plants depending on the presence or absence of competitors? In hermaphrodite animals, the social context (e.g. group size) can clearly influence male-female allocation.

In this study on violets, a hermaphrodite annual, our results indicate that sex allocation may not only be size dependent and influenced by soil nutrients, but also affected by presence of a root competitor. Taking the additional aspect of social environment into account also in studies on sex allocation in plants has the potential to increase our understanding of sex allocation across taxa.  This knowledge might help us answer difficult questions such as how evolutionary transitions can occur between breeding systems.

In the new early view paper “Do physical plant litter traits explain non-additivity in litter mixtures? A test of the improved microenvironmental conditions theory”, Marika Makkonen and co-workers, present a new theory on decomposition rates. Here’s their own summary of the paper:

Terrestrial plant litter decomposition is a key component in carbon flux models. The models and thus the predictions they produce could be improved by ensuring the comprehensiveness of the variables included in the model and the close resemblances between nature and the input data. Usually the input data is derived from litter monoculture studies and this creates a crucial source of error, as monocultures do not present well the majority of land cover. Importantly decomposition rates usually differ between litter monocultures and mixtures. The causes for this non-additive effect are still debated and unclear. One plausible theory suggests that the non-additivity of litter mixtures derives partly from improved microclimatic conditions given by physically more diverse plant species in mixtures compared to monocultures. The physical characteristics of litter determine e.g. water acquisition and retention and thus alter the microenvironmental conditions determining the habitat and resource availability for decomposers.

We tested this theory in a dry subarctic birch forest in the Swedish Lapland in two contrasting moisture conditions. By testing some water holding capacity (WHC) traits, we found clear support for this theory and thus our results strongly encourage the inclusion of plant litter physical traits as the predictors of the decomposition rates. Yet the modeling will face more challenges as we found the direction of non-additivity (positive or negative deviation compared to monocultures) in litter mixtures to vary between climatic (moisture) conditions. Namely we found that the higher dissimilarity in WHC traits between the component litter species in a mixture increased synergistic effects in litter mixtures under limiting moisture conditions whereas, increased antagonistic effects were observed under improved moisture conditions. We also observed differences in non-additivity, its relation to WHC traits and their modifications by different climatic conditions between litter mixtures of varying decomposability further obscuring the process. Although the non-additivity of litter mixture remains complex, some major advances were made by this study.

At least here in southern Sweden, the autumn colours have been fantastic this year! As an evolutionary ecologist one starts wonder: why does trees differ in level of coloration? Is it only a benefit to the tree? Or are there costs associated with it as well? And why are some leaves red early in spring? In the new Early View paper, “Red young leaves have less mechanical defence than green young leaves”, Ying-Zhuo Chen and Shuang-Quan Huang have found answers to some of these questions. Here is a short version by Shuang-Quan Huang:

People in North Temperate Zone often enjoy seeing colorful leaves in autumn, an obvious phenomenon in deciduous forests. Evolutionary biologists Hamilton and Brown (2001) considered that autumn leaf coloration is expensive because it involves the costs of pigment synthesis, resource loss and loss of primary production (photosynthesis). A functional hypothesis proposed by Hamilton & Brown (2001) and Archetti (2000) suggest that leaf redness could be an adaptive strategy as a warning signal reducing insect attack (anti-herbivory hypothesis), but is still largely controversial.

Many species have red young leaves in spring. For example, an investigation of tropical plants in a Nature Reserve, Singapore showed that 60% species with young leaves were red (see Dominy et al. 2002). The anti-herbivory hypothesis has also been adopted to explain color change during leaf development. We are interested in why so many species produce constant green leaves in its life cycle if leaf-color change involves an obvious benefit (less herbivory). A similar question was asked by David Lee (2002) who argued that if anthocyanins in leaves confer some physiological/selective advantage, how do the species lacking anthocyanins compensate?

To test whether green leaves reduce herbivory by physical defense as an alternative to the supposed warning signal of red leaves, we conducted comparative analyses of leaf color and protective tissues of 76 woody species around our campus Wuhan University, a subtropical area in central China. We found that the species with green young leaves showed a significantly higher incidence of enhanced cuticle, multiple epidermis, and trichomes compared to species with red young leaves. This analysis suggests that green leaves may compensate for the lack of anthocyanins by adopting enhanced physical defense. Our finding of relatively poor mechanical protection in red young leaves may provide new evidence for the adaptive explanation of leaf color change.

In the new paper “Adaptive foraging allows the maintenance of biodiversity of pollination networks” Fernanda S. Valdovinos and her colleagues present a new population-dynamics model for plant-pollinator interactions:

 Here’s Fernanda’s summary of the model: One of the main novelties of our work is the new model of mutualistic networks that we proposed. Our model includes the trophic dimension of mutualistic interactions, by incorporating a separated equation for the dynamics of the resources that plant species offer to their animal visitants. In this way we could incorporate to the analysis of mutualistic networks the next biologically important process: 1) the production and animal consumption rates of plant rewards, 2) the competition and/or facilitation among plants via shared pollen/seed animal vectors, 3) the competition among animals for plant rewards, and 4) the animals’ allocation of foraging efforts. These processes were neglected by the traditionally used models on mutualistic networks, which simply represent mutualistic relationships as phenomenological positive effects among species. I think that these four processes may affect the interplay of network structure and dynamics that some studies have documented during the last years, like are the effects of nestedness, connectance and richness on the species persistence of those networks.

Alien, invasive species are an increasing threat to biodiversity. In their paper “Competitive outcomes between two exotic invaders are modified by direct and indirect effects of a native conifer”, Kerry Metlen and co-workers has studied what two invasive species – a grass and a herb – and how they are affected by a native pine. Here, Kerry gives a short background to their study:

This research was inspired by a very striking pattern observable at undisturbed sites in the intermountain grasslands of western Montana, USA; Centaurea stoebe is supremely dominant in open prairie but virtually absent under the canopies of large ponderosa pines growing in the grassland.  At disturbed sites, any component of the native vegetation has been removed, C. stoebe appears to then move in aggressively, suggesting that some complex interaction among species drives this very simple pattern. 

 Extensive field observations confirmed the pattern that had seemed so obvious, as at this site just east of Hamilton, Montana, USA.  Germination experiments and extensive litter manipulation – in the field and in the greenhouse gradually allowed us to tease apart these complex interactions.  This fantastic adventure, lead us to discover that direct effects between species were insufficient to explain patterns of invasion of C. stoebe and Bromus tectorum and that shifting interactions among species gave a more complete picture of this dynamic plant community.

That predator-prey interactions can be temperature-dependent is something that Angela Laws and Anthony Joern shows in the new Early View paper in Oikos “Predator–prey interactions in a grassland food chain vary with temperature and food quality”

Read their background story here:

“Grasshoppers are important components of most grassland ecosystems.  These abundant herbivores can influence many ecosystem processes such as nutrient cycling and primary productivity.  But the effects of grasshoppers on ecosystem processes often depend on the outcome of their interactions with other species, including predators.  For example, spiders are common predators of grasshoppers that alter grasshopper behavior and can limit grasshopper population size. But the outcome of species interactions can be sensitive to changes in many biotic and abiotic environmental factors.

We were interested in learning how temperature can influence predator-prey interactions between grasshoppers and wolf spiders.  Ectothermic organisms like grasshoppers and spiders are likely to be especially impacted by shifting temperatures, because temperature affects many physiological processes including feeding, activity, and digestion.  But temperature may also alter species interactions with effects on food web functioning.  In our system, grasshoppers prefer warm temperatures and are active during the day while wolf spiders prefer cooler temperatures and are crepuscular.  Therefore, we predicted that shifting temperatures can alter predator effects on grasshoppers by expanding (through cooling) or contracting (through warming) the total amount of time each day that both grasshoppers and wolf spiders are active.

We conducted a three-year field experiment to test these predictions using common species of grasshopper (Orphulella speciosa) and wolf spider (Rabidosa rabida). We set up field cages and stocked them with grasshoppers only or grasshoppers and spiders.  To alter temperature, we surrounded some of the cages with temperature chambers constructed of steel frames covered with shade cloth (decreased temperatures) or with plastic sheeting (increased temperatures).  Other cages were left uncovered as a control.  The roofs of these temperature chambers were mounted on garage door tracks and could be opened and closed.  The roofs only covered the cages during the morning and were left open for most of the day.

We found that spiders had strongest effects on grasshopper survival in the cooled treatments, and weakest effects on grasshopper survival in the warmed treatments, as predicted.  In some years, this led to the appearance of a trophic cascade (an indirect effect of predators, where predator presence leads to an increase in plant biomass) in cooled treatments, but not warmed treatments.   Our results show that the outcome of predator-prey interactions between grasshoppers and wolf spiders, and their effects on plant production, can shift with temperature.  Our data also suggest that wolf spiders may be less effective at limiting the size of some grasshopper populations under warmer conditions.”

Is there really a connection between biodiversity and conservation and Internet? Oh, yes, read Michal Zmihorski and his colleagues new Early View paper in Oikos, “Ecological correlates of the popularity of birds and butterflies in Internet information resources”.

Below, Michal tells us what made him and his co-workers to do this analyses:

“The idea concerning wildlife in the Internet resulted from a simple observation. Namely, we noted that different species are popular in the Internet whereas others are relatively rare. For each query Google provides the number of web pages containing the searched word(s) (here the name of a bird or butterfly). Consequently, we searched for possible mechanisms explaining the differences. More specifically, we expected that the patterns of popularity and rarity in the web were not random and should be somehow linked to the phenotype of particular species. Therefore we selected some basic characteristics of species, such as body size or migratory behaviour, and checked their importance in explaining the popularity on the internet. We excluded species whose names had more than one meaning. Initially we worked on Polish names of Polish birds but, following editors’ advice, we extended this to English names of British butterflies.

Several characteristics related to ecology and morphology of species were associated with their popularity in society. This in turn may have some obvious consequences for selection of species for conservation actions (e.g. as flagship species). We suggest that conservationists may use some phenotypic features of species in a more systematic manner to select for flagship species. However, to be honest, this is not of primary interest to us. The most exciting aspects of the association between phenotype and popularity is related to possible feedback, i.e. profits that popularity brings to a given species. First of all, we showed that there is some filtering of “colonization” of the internet by birds and butterflies (some features make species more effective in this “colonization” process). Secondly, the assumption that popularity in society is profitable for species seems to be true and may be related to the fact that organisms which are commonly known and well recognized by peoples may benefit from e.g. artificial feeding, nest-boxes, nest protection from predation and devastation, conservation actions, effective fund raising and so on (it is not easy to find references confirming this assumption, fortunately, we do not have to provide any in text for an Oikos blog!). If this is so the following mechanism can be proposed: the phenotypic features that makes a species popular in the Internet may also affect its fitness (because species that are popular in society may benefit from their popularity). Of course, the proposed mechanism has several weak points and needs to be confirmed, but in our opinion may be a catalyst for further studies. What is important is that if the mechanism works this means that natural selection may partially go through the virtual world of the internet, and such an idea is something new.

            All your comments and suggestions (including proposals for cooperation) concerning the topic of our study are highly welcomed. You have full text access to this content“

How close to a relative should one settle? David Aguirre et al have shown that relatedness has an effect on colonization and settlement in some species, at least.

Here’s David’s summary of the paper that is now on Early View in Oikos:

“In organisms with sessile adults (e.g. many plants and marine invertebrates) variation in the density of colonisers is known to have a profound influence on the structure of populations and communities. Recent studies also indicate that the relatedness among interacting adults can be an important driver of differences in ecological performance among populations. Thus, it is surprising that few studies have examined the effects of relatedness on the non-adult life-history stages, and thereby the effects of relatedness on colonisation processes. In our study we bridged the gap between these two lines of ecological enquiry, and found that the effects of relatedness on colonisation differed in direction and magnitude in four sessile marine invertebrates.”

In the new Oikos paper (now on Early View), “Simulated responses of moose populations to browsing-induced changes in plant architecture and forage production”, John Pastor and Nathan R. de Jager present a model examining how tree crown architecture affects moose populations. Here, they give a background to the study:

“In the recently published paper, “Simulated responses of moose populations to browsing-induced changes in plant architecture and forage production”, we report the results from a model we developed nearly a decade ago as part of Nate’s Master’s thesis at the University of Minnesota-Duluth. The model examines the feedback effects of moose browsing-induced changes in plant architecture on moose population dynamics. We were able to construct the model because of a very well thought out and executed experiment in northern coastal Sweden (Persson et al. 2005 a, b). Inga-Lill Persson and her colleagues  annually removed plant tissue from study plots in proportion to different moose population densities and also added corresponding amounts of urine and fecal material. By measuring the architectural responses of different tree species to simulated moose densities (De Jager and Pastor 2008, 2010) we were able to ask a very simple question: Can the forage produced by trees that have been previously browsed in proportion to known moose densities support the same moose population densities over the long-term? Our main finding of the field study was that some properties of the crown architecture of deciduous trees, such as fractal dimension and twig density, responded quadratically to increased moose population density. At intermediate moose densities, these properties more than compensate for reductions in twig size, leading to small increases in forage production.

Our approach to constructing the model was extremely simple, assembling these equations for the architectural responses of plants to known moose population densities and the winter food requirements of moose, but ignoring other known factors that influence moose population dynamics (e.g. animal feeding rates, population demographics) and other known effects of moose on ecosystems (e.g. changes in soil fertility). The point was to see if these architectural responses in isolation could in principle determine moose population densities and dynamics. In fact, it was the simplicity of the model that kept us from submitting it as a manuscript for several years. John developed a renewed interest in the model after receiving positive comments from colleagues in Sweden following a presentation in  2010. Indeed, the editorial reviewers at Oikos liked the model and our paper because of its simplicity, not in spite of it.

It turns out that the architectural responses of plants that we measured can produce realistic moose population densities for northern Sweden  (an average of ~10-15 moose/1000 ha). But these population densities were only sustainable at the sites with the highest productivity and with species compositions heavily weighted toward deciduous trees, which can overcompensate for lost tissue due to moose browsing.  One of the new things we found was the quadratic responses of plant architecture to moose population density, especially those of birch, produced oscillations in moose populations on highly productive sites. The lessons we learned from this model were, first, that architectural responses of plant crowns to browsing may play a more important role in regulating moose population density than previously suspected and, second, that these architectural responses might cause complex population dynamics such as population cycles.”

Link to Persson et al. 2005 a

Link to Persson et al. 2005 b

Link to De Jager and Pastor 2008

Link to De Jager and Pastor 2010

Oh, yes, fish have personalities as well! Matthew Edenbrow and his colleague has digged deeper into this to unravel the basis behind it. Now on early View: “Environmental and genetic effects shape the development of personality traits in the mangrove killifish Kryptolebias marmoratus”

Here’s Matthew’s own story:

Personality is defined as individual consistency in behaviour over time or situations. In humans it is obvious that we all differ in our personalities with some individuals being risk takers or bolder than others. While personality is clearly part of what it means to be human, there is considerable evidence suggesting that these traits are also exhibited throughout the animal kingdom. In particular, personality has been documented in several animal groups including primates, reptiles, fish and even insects, suggesting that personality is not only important but that it evolved early. At present, however, we have little insight into what factors determine individual differences in personality. Research suggests that experiences of different environments during development may underpin personality variation. In addition, growth as well as age at sexual maturity may also be important; with fast growth/early maturity suggested to generate bolder personalities. In this study we used the naturally “clonal” mangrove killifish (Kryptolebias marmoratus) as our study organism. This species is exciting because it permits us to investigate how genetically identical individuals adjust behaviour, growth and reproductive development depending upon the environment experienced. In this study we reared several genetically identical individuals in three rearing environments: 1) the presence of siblings, 2) reduced food and 3) simulated predation risk. We then investigated growth and three personality traits: exploration, boldness, and aggression, at three stages of development. Our results indicate that only individuals exposed to simulated predation risk exhibited behaviour consistency, suggesting that risk perception during early life stages is likely to be important in personality development. In addition, each of our rearing environments resulted in different growth rates and age at sexual maturity yet these differences were not key drivers of the resulting behavioural differences we observed

Now online: Perea et al. “Context-dependent fruit-frugivore interactions: partner identities and spatio-temporal variations”

Here Ramon Perea summarizes the study:

Plants are able to use animals as vectors for the dispersal of their seeds. Many fleshy fruits constitute a food attractive for different vertebrate species, that usually ingest jointly the edible pulp and the seeds, which are later defecated or brought up in suitable conditions for germination. Studies on this kind of plant-animal mutualism, called endozoochory, are numerous, but usually refer to only one pair of mutualists, or are made during one fruiting season or at only one place.

Does seed dispersal by mammals depend on the spatio-temporal context in which the interaction takes place? For instance, species abundances, specific seed crops, availability of alternative foods or vegetation structure usually change from year to year or from one habitat to another at the same locality. Many of these changing factors might affect important attributes of the plant-animal interaction. In our particular case of seed dispersal, the environmental context might modify, for example, the quantity of seeds dispersed (interaction strength) or the quality of dispersal (seed treatment, deposition on suitable sites for germination and survival, etc.), which could eventually alter the so-called sign of the interaction (from a highly successful dispersal –mutualism- to a highly unsuccessful dispersal –antagonism).

Our field work was performed in the Doñana National Park (SW Spain), under Mediterranean conditions, where we collected about 1600 faeces of a whole assemblage of fruit-eating mammals (frugivores: red fox, badger, red deer, wildboar and rabbit).  About 300,000 seeds of fruit-bearing plants were recovered of these faeces, measuring frequency of seed occurrence, plant species and seed damage for three different habitats.

For each particular fruit-frugivore pair, the interaction strength largely varied with the spatio-temporal context (year and habitat) at our local scale, leading to a low specificity across the seed-frugivore network. Frugivory and potential endozoochory should not be simply considered a mutualism leading to successful seed dispersal, but a rather variable relationship along the mutualism-antagonism continuum, depending on the ecological context.

First author Cene Fiser gives a short version of their paper “Coevolution of life history traits and morphology in female subterranean amphipods“. 

Fine-tuning evolution often requires compromises. Maximizing female’s fitness by optimization egg number and egg size to the environmental demands is a classic trade-off in evolutionary biology. But, can co-evolving morphological changes affect or even avoid this trade-off? We compared Niphargus species found in springs and in deep caves and showed that cave species are larger, stouter, have larger eggs, yet the number of eggs is not lower compared to spring species. These changes seem to be a result of decreased fluctuations of abiotic factors and of decrease in food availability in deep caves compared to springs. The environmental gradient most likely presents major source of selection that affected all herein studied morphological and life history traits. However, we have shown that the co-evolution of biological traits can modify the otherwise expected outcome of selection. We suggest that increased body size, that also enables storage of more energy, enables allocation of additional nutrients in egg size, yet the number of eggs can remain the same. Additionally, as larger eggs require better supply with water for aeration, bigger species have also modified body shape.

In the study “Density- and trait-mediated top–down effects modify bottom–up control of a highly endemic tropical aquatic food web” Christopher Dalton and co-workers have looked at bottom-up and top-down effects in anchialine ponds on Hawaii. Here’s Chrsitopher’s own story about the study:

For centuries, early Hawaiian residents divided land on the island into expansive parcels known as ahupuaʻa, with each ahupuaʻa containing all of the resources the residents would need to survive (water, food, shelter). Ahupuaʻa typically ran in radial lines extending from the top of the nearest volcano (Mauka; near the mountains) to the shore of the ocean (Makai; near the ocean). The expression Mauka to Makai lives on as an important model for island conservation today, emphasizing that the spectacular and unique biodiversity of these islands cannot be preserved without understanding the links between ecosystems.

Perhaps no single Hawaiian ecosystem better reflects the necessity of landscape-scale conservation as the anchialine ponds of coastal Hawaiʻi, connected through porous lava substrate to both tidal seawater and fresh groundwater. One of the most striking organism in the ponds is the endemic atyid shrimp, Halocaridina rubra (locally known as ōpaeʻula, or red shrimp).  This locally abundant invertebrate shows diel migration between daytime refuges in subterranean environments and nighttime foraging in productive surface habitats. In anchialine pools, the grazing of ōpaeʻula is often attributed a keystone function for maintaining a diverse and tuft-like epilithic crust of algae, cyanobacteria and heterotrophic bacteria.

We assess the roles of nutrients and invertebrate consumers in anchialine pond food webs by taking advantage of long-term, whole-ecosystem anthropogenic modification of bottom-up (nutrient enrichment) and top-down (grazing) controls. This study provides insight at the ecosystem scale for the interactions between top-down and bottom-up control in a system of dire need of information to direct management practices against threats from development and invasive species.

We collected quantitative samples of the epilithon quantity and composition, the abundance (day and night) of ōpaeʻula, the presence of fish and the dissolved nutrient concentrations. Sometimes this meant getting wet in the deepest pools, and sometimes it meant wading through algal and detrital mats up to half a meter deep. In the end, we captured a snapshot of the relatively simple food web structure and nutrient availability of twenty pools.

This study provides whole-ecosystem scale insight into the relative influence of bottom-up and both trait and density mediated top-down effects in pool food webs, and it also provides evidence to help guide management decisions. Our research suggests the ecological benefits of mitigating nutrient pollution are comparable to those of removing predatory, invasive fish, and monitoring these two factors can prevent the dramatic ecological change we observed in high nutrient ponds with fish.

Ultimately, preservation of Hawaiian anchialine ponds requires a perspective beyond the edges of these ecosystems. The nutrient enrichment that we observed in anchialine ponds was associated with land use (resorts, hotels and golf courses) immediately surrounding those ponds.

To truly understand and protect these hotbeds of endemism into the future, however, research must look from Mauka to Makai and assess the role of landscape context in driving change in these unique ecosystems.

One of the new papers online in Oikos is about the importance of full understanding of demography of wild populations for management programs. One of the authors, Eleanor Devenish-Nelson gives us here the background to the study “Demography of a carnivore, the red fox, Vulpes vulpes: what have we learnt from 70 years of published studies?”:

The successful management of wildlife depends on the ability to predict the consequences of management actions. That, in turn, often requires a good knowledge of a species’ demography and dynamics. We can use that knowledge, of issues such as birth and death rates, to produce predictive models with which we can simulate different management strategies. In situations in which we don’t know enough about a population of interest, it is common to use ‘surrogate data’ (demographic parameters from other populations of the same, or closely related, species) in order to construct predictive models.

    One species of considerable management concern is the red fox. Red foxes are widely hunted and are important hosts for several diseases. The management of red foxes is often contentious, invoking strong feelings in many people. We wanted to produce what we thought would be a straightforward model of red fox dynamics, as the foundation for answering several applied questions. At first glance, foxes appear to be well studied: a quick search brings up over 1000 papers on aspects of their demography. However, an initial assessment of that literature revealed that the demography of this widespread species was surprisingly poorly known, with limited data for most populations and, even for several better-studied populations, missing information on birth or death rates. Some of the demographic rates that we collated were highly variable between populations – but was this a result of genuine differences, or of poorly defined or presented data?

            Although the available data on red fox populations are often uncertain and frequently based on relatively short-term studies, we were able to analyse the demography of eight different populations. Those analyses revealed considerable variation in demography among the populations. Differences were sufficient to be of consequence for management. More importantly, by substituting demographic parameters between fox populations, we showed that using surrogate data could often be very misleading for managers. Data substitution is often a necessity but our analyses suggest that it can guide how managers prioritise measuring demographic parameters for their focal populations. In general, for example, a model using surrogate data on the probability with which females breed will be more misleading than if surrogate data on litter size is used. Hence, managers should prioritise accurate estimates of the former.

            Overall, what started out as a simple study revealed the significant gaps in our understanding of fox demography, especially in relation to the selection pressures this species faces, such as hunting, disease and a highly variable climate across its range. Owing to variability between populations and the dangers of using surrogate data, the need for more widespread, long-term monitoring is clear. Emerging technologies should be harnessed to make routine the widespread collection of demographic data on wildlife populations. This paper emphasises why a better understanding of the demography of fox populations is of relevance for management. 

Photo  © Paul Cecil

In the new Early View paper  “The influence of abundance on detectability” McCarthy and co-workers explore the relationship between actually being detected and being there.

Here is Michael McCarthy’s own story on the study, the paper and the results:

How hard do we need to look to be sure a species is absent when it is not detected? This question is fundamental in ecology. It is relevant when determining the appropriate level of survey effort, when compiling lists of species, when determining the extinction of species, and when developing surveillance strategies for invasive species.

Without sufficient survey effort, species are not detected perfectly. Imperfect detection arises because species may be temporarily absent, hidden from view, or simply require extra effort to find. The detectability of species can be defined by the rate at which individuals of a species (or groups of those individuals) are encountered.

Detectability of species will increase with abundance, all else being equal. But what is the nature of that relationship? We present a model of this relationship, with the rate of detection being a power function of abundance (Fig. 1). The exponent for this function (b) will equal 1 if individuals are encountered independently of one another. When clustering of individuals increases with abundance, we expect this exponent to be less than 1, but greater than 0.

As values for the scaling exponent approach 0, the detection rate becomes less sensitive to abundance (Fig. 1). Knowing how detection rate scales with abundance can assist when determining detection rates of rare species. This is important because detecting rare species is often important, yet estimates of detection rate are often most uncertain for these species. A scaling relationship would allow extrapolation of detection rates to cases when species are rare.

The field trials were conducted in a remnant of eucalypt woodland in Royal Park near The University of Melbourne searching for plants and coins, in an exotic grassland in Royal Park searching for planted Australian native species, and in eastern Australian forests searching for frogs.

Nothing can spoil a vacation as efficiently as a rainfall. And nothing affects a farmer’s mood as rain- it’s presence or it’s abscence. Too much or too litte. Always an issue worth of debating.

In one of the latest Early View papers in Oikos, “Seasonal, not annual precipitation drives community productivity across ecosystems”, Todd M. P. Robinson, and co-workers study the effects of precipitation on plant production in various ecosystems.

Below, the authors give a short background to the study:

While any farmer will tell you how important it is to receive rainfall at certain times of the year, many ecological plant studies focus on how total annual rainfall affects plant production. After a meeting for the US Long Term Ecological Research Network (LTER), a group of us decided to test just how helpful it would be to focus on shorter time scales by examining whether rainfall during either the beginning, middle, or end of the growing season correlated with total aboveground production during the same season. We found that focusing on the amount of rain across one or two short time periods usually gave as much or more information on plant production as annual rainfall amounts. This was generally true across a wide array of communities from desserts to forests, despite the large difference in vegetation types and total available water.

As a graduate student working group with members from multiple institutions, we supplemented our initial LTER funded workshop by using Skype and email to coordinate our analyses and writing. As young scientists, we are excited that our cross-site analysis can contribute to the development of a more nuanced approach to plant-rainfall interactions. We expect that the combination of our work with other advances in plant-water dynamics will improve our understanding of how current and future variation in precipitation will affect plant communities.