Intrinsic and climatic factors in North-American animal population dynamics

BACKGROUND: Extensive work has been done to identify and explain multi-year cycles in animal populations. Several attempts have been made to relate these to climatic cycles. We use advanced time series analysis methods to attribute cyclicities in several North-American mammal species to abiotic vs. biotic factors. RESULTS: We study eleven century-long time series of fur-counts and three climatic records – the North Atlantic Oscillation (NAO), the El-Niño-Southern Oscillation (ENSO), and Northern Hemisphere (NH) temperatures – that extend over the same time interval. Several complementary methods of spectral analysis are applied to these 14 times series, singly or jointly. These spectral analyses were applied to the leading principal components (PCs) of the data sets. The use of both PC analysis and spectral analysis helps distinguish external from intrinsic factors that influence the dynamics of the mammal populations. CONCLUSIONS: Our results show that all three climatic indices influence the animal-population dynamics: they explain a substantial part of the variance in the fur-counts and share characteristic periods with the fur-count data set. In addition to the climate-related periods, the fur-count time series also contain a significant 3-year period that is, in all likelihood, caused by biological interactions

Eco-evolutionary dynamics in a disturbed world: implications for the maintenance of ecological networks [version 1; referees: 2 approved]

Past management of exploited species and of conservation issues has often ignored the evolutionary dynamics of species. During the 70s and 80s, evolution was mostly considered a slow process that may be safely ignored for most management issues. However, in recent years, examples of fast evolution have accumulated, suggesting that time scales of evolutionary dynamics (variations in genotype frequencies) and of ecological dynamics (variations in species densities) are often largely comparable, so that complex feedbacks commonly exist between the ecological and the evolutionary context (“eco-evolutionary dynamics”). While a first approach is of course to consider the evolution of a given species, in ecological communities, species are interlinked by interaction networks. In the present article, I discuss how species (co)evolution in such a network context may alter our understanding and predictions for species coexistence, given the disturbed world we live in. I review some concepts and examples suggesting that evolution may enhance the robustness of ecological networks and then show that, in many situations, the reverse may also happen, as evolutionary dynamics can harm diversity maintenance in various ways. I particularly focus on how evolution modifies indirect effects in ecological networks, then move to coevolution and discuss how the outcome of coevolution for species coexistence depends on the type of interaction (mutualistic or antagonistic) that is considered. I also review examples of phenotypes that are known to be important for ecological networks and shown to vary rapidly given global changes. Given all these components, evolution produces indirect eco-evolutionary effects within networks that will ultimately influence the optimal management of the current biodiversity crisis

Coexistence via Resource Partitioning Fails to Generate an Increase in Community Function

Classic ecological theory suggests that resource partitioning facilitates the coexistence of species by reducing inter-specific competition. A byproduct of this process is an increase in overall community function, because a greater spectrum of resources can be used. In contrast, coexistence facilitated by neutral mechanisms is not expected to increase function. We studied coexistence in laboratory microcosms of the bactivorous ciliates Paramecium aurelia and Colpidium striatum to understand the relationship between function and coexistence mechanism. We quantified population and community-level function (biomass and oxygen consumption), competitive interactions, and resource partitioning. The two ciliates partitioned their bacterial resource along a size axis, with the larger ciliate consuming larger bacteria than the smaller ciliate. Despite this, there was no gain in function at the community level for either biomass or oxygen consumption, and competitive effects were symmetrical within and between species. Because other potential coexistence mechanisms can be ruled out, it is likely that inter-specific interference competition diminished the expected gain in function generated by resource partitioning, leading to a system that appeared competitively neutral even when structured by niche partitioning. We also analyzed several previous studies where two species of protists coexisted and found that the two-species communities showed a broad range of biomass levels relative to the single-species states

Multidimensionality of plant defenses and herbivore niches: implications for eco-evolutionary dynamics

International audiencePlant defenses are very diverse and often involve contrasted costs and benefits. Quantitative defenses, whose protective effect is dependent on the dose, are effective against a wide range of herbivores, but often divert energy from growth and reproduction. Qualitative defenses often have little allocation costs. However, while deterrent to some herbivores, they often incur costs through other interactions within the community (eg, decrease in pollination or attraction of other enemies). In the present work, we model the evolutionary dynamics of these two types of defenses, as well and the evolutionary dynamics of the herbivore niche. We assess the effects of such evolutionary dynamics for the maintenance of diversity within the plant-herbivore system, and for the functioning of such systems under various levels of resource availability. We show that the two types of defenses have different implications. Evolution of quantitative defenses often helps to maintain or even increase diversity, while evolution of qualitative defenses most often has a detrimental effect on species coexistence. From a functional point of view, increased resource availability selects for higher levels of quantitative defenses, which reduces top-down controls exerted by herbivores. Resource availability does not affect qualitative defenses, nor the evolution of the herbivore niche. The growing evidence that plant defenses are diverse in types, benefits and costs has large implications not only for the evolution of these traits, but also for their impacts on community diversity and ecosystem functioning

Evolutionary response of plant interaction traits to nutrient enrichment modifies the assembly and structure of antagonistic-mutualistic communities

International audience1. Nutrient enrichment is one of the major threats acting on natural communities. The ecological consequences of this disturbance for ecosystems have been largely studied, but we still have little knowledge on its evolutionary effects at community scale. We are interested in the evolutionary consequences of nutrient enrichment for plant interaction traits, embedded in complex communities made of antagonistic and mutualistic interactions. 2. We built a mathematical model of a plant-pollinator-herbivore community confronted by nutrient enrichment. Plants have an interaction trait that is involved in an ecological trade-off. An increase in this trait, leading to more attractive phenotypes, increases the strength of both interactions with pollinators and herbivores. A lower value of this trait leads to defensive phenotypes with weak interactions with both herbivores and pollinators. We use the framework of adaptive dynamics to study the evolutionary dynamics of this kind of traits and the consequences for community dynamics. 3. We found that evolutionary dynamics of plants modify the assembly of the community along a nutrient enrichment gradient. Due to top-down controls, herbivory leads to priority effects when only ecological dynamics are considered. Evolution of the plant interaction trait alleviates this priority effect and facilitates community assembly. In the three-species community, we find that nutrient enrichment leads to more defended phenotypes of plants, at the expense of pollinator attraction. 4. We find that, when the ecological trade-off between pollination and herbivory is convex, evolution of interaction trait may lead to plant diversification. Two plant phenotypes then coexist in the community, one which is highly attractive and one which is highly defensive. 5. Synthesis. Our results suggest that accounting for evolutionary dynamics will profoundly modify the dynamics of communities in the face of nutrient enrichment. Both community assembly and equilibrium dynamics are altered and enrichment may even lead to diversification. These results advocate for the development of an eco-evolutionary theory of nutrient enrichment and may be particularly important in agro-ecosystems relying on fertilization

Balancing yield with resilience and conservation objectives in harvested predator-prey communities

International audienceThe global overexploitation of fish stocks is endangering many marine food webs. Scientists and managers now call for an ecosystem-based fisheries management, able to take into account the complexity of marine ecosystems and the multiple ecosystem services they provide. By contrast, many fishery management plans only focus on maximizing the productivity of harvested stocks. Such practices are suggested to affect other ecosystem services, altering the integrity and resilience of natural communities. Here we show that while yield-maximizing policies can allow for coexistence and resilience in predator–prey communities, they are not optimal in a multi-objective context. We find that although total prey and predator maximum yields are higher with a prey-oriented harvest, focusing on the predator improves species coexistence. Also, moderate harvesting of the predator can enhance resilience. Furthermore, increasing maximum yields by changing catchabilities improves resilience in predator-oriented systems, but reduces it in prey-oriented systems. In a multi-objective context, optimal harvesting strategies involve a general tradeoff between yield and resilience. Resilience-maximizing strategies are however compatible with quite high yields, and should often be favored. Our results further suggest that balancing harvest between trophic levels is often best at maintaining simultaneously species coexistence, resilience and yield

Stable Coexistence in Plant-Pollinator-Herbivore Communities Requires Balanced Mutualistic vs Antagonistic Interactions

International audienceEcological communities consist of multiple species interacting in diverse ways. Understanding the mechanisms supporting coexistence requires accounting for such a diversity. Because most works focus either on mutualism or predation, how pollination and herbivory interactively determine the stable coexistence in plant-pollinatorherbivore communities is still poorly understood. Studying the typical three-species module of such communities, we determine the conditions allowing stable coexistence then investigate how its maintenance constrains the relative interaction strengths. Our results show that coexistence is possible if pollination is sufficiently strong relative to herbivory, while its stability is possible if herbivory is sufficiently strong relative to pollination. A balance between pollination and herbivory is therefore required. Interestingly, shared preferences for plant phenotypes, that would favor such balance, have been frequently reported in the empirical literature. The identified ecological trade-off between attracting pollinators and deterring herbivores therefore also appears as an emergent property of stable plant-pollinator-herbivore communities