Ecosystems are constantly facing numerous natural and human induced perturbations, occurring both over short time scales (e.g. extreme climate events) and long time scales (e.g. change in land use). Such perturbations often alter the dynamics of ecological communities and worsen the provision of ecosystem services to human populations. Ecological communities are key elements of the response of ecosystems to global change perturbations. To assess and mitigate ecosystem response to perturbations, we need to understand how perturbations affect the diversity of species as well as the complex interactions between them, and how these effects in turn determines ecosystem stability. However, knowledge on this issue is still largely lacking, partly because the different facets of the links between global changes, community structure and ecosystem stability have been mostly considered by disconnected ecological research pieces. The project ECOSTAB aims to bring the experimental, empirical and theoretical knowledge needed to assess and understand how different components of global changes affect community structure and ecosystem stability, in terms of both the variability of ecosystem properties over time and the resistance and resilience of ecosystem properties to extreme climate events. To achieve this ambitious objective, ECOSTAB brings together a consortium of researchers with highly complementary expertise on community ecology, food web structure, ecosystem functioning, aquatic and terrestrial ecosystems, large database analyses, ecological models and management of large experimental infrastructures, to combine: (1) A unique experimental test of the consequences of two major components of global changes (eutrophication and top predator loss) and their interaction on food web structure and stability of freshwater ecosystems at fine temporal resolution. (2) An unprecedented assessment on a large temporal and spatial scale of the effects of land use alterations and climatic variability on the trophic structure of terrestrial and aquatic communities, and on the stability of large functional groups having a commercial or patrimonial value (e.g. commercial fishes, birds, butterflies). (3) Novel models with predictions connected to the stability of natural ecosystems to understand the consequences of different components of global changes (e.g. climate variability, nutrient enrichment) on stability of ecosystem functioning in complex food webs. To our knowledge, ECOSTAB would be one of the first project to tackle the study of the consequences of multiple perturbations on different components of community and ecosystem stability (variability as well as resistance and resilience to extreme climate events). Furthermore, it would do so at very different temporal and spatial scales by exploiting the synergies between experimental, empirical and theoretical approaches. In addition to novel and important scientific results, we expect that ECOSTAB’s results would also bring important knowledge on how to manage ecosystems for conserving the structure of natural communities and to restore or improve the stability of important services such as water purification, primary or secondary productivity.

What are the proximate mechanisms – at the individual level – underlying the assembly and dynamics of ecological communities? Despite its apparent universality, this question is still puzzling scientists – and challenges their methodological limits. Global changes impact community diversity, structure and, but how these changes are rooted in individual dynamics remain poorly understood. Modeling the dynamics of ecological communities is difficult due to the complex dynamics of interacting species, and the need to integrate information across several biological levels (individuals – populations – communities). Yet, to shed lights on the processes underlying observed community modifications, knowing to what extent each species contribute to the direction and intensity of these modifications is of paramount relevance. For instance, following climate change or human disturbance, conservation and management implications are likely to be different if only two or three interacting species are responsible for an observed change in a community-based index. In the DEMOCOM project, we will develop an integrated statistical framework for estimation and inference about community dynamics via the development of a multispecies demography, bringing together concepts, predictions and tools from both fields of demography and community ecology. Demography aims at capturing variation in size, ages and ontogenic stages within a population. Although well developed for single-species dynamics, demography has received little attention in community ecology. We will develop a statistical framework to fit multispecies stage-structured models to data and partition the contribution of intra-specific and inter-specific demographic variations to changes in community composition (WP1). In particular, i) we will devise community sensitivity analyses to explore how small changes in the demographic rates of species and in the strength of interaction within and between species may affect the structure and resilience of communities, ii) we will extend our deterministic multispecies demographic models to incorporate stochasticity and fully account for environmental variability and iii) we will integrate mathematical structured multispecies models with statistical approaches to properly integrate the complexity of community dynamics and accommodate the various sources of uncertainty at play. Motivated by case studies on wild populations, we will investigate the role of inter-specific interactions in shaping the community-level response to climate change and management interventions in bird, fish and mammal communities (WP2). The data are owned and collected by the partners of the consortium. Besides, these case studies have been carefully selected to start working with relatively simple systems in which we have a few species and explicit interactions (seabirds and tunas), then to proceed with more complex systems in which we have more species with many possible interactions (common birds and large carnivores and their ungulate preys). Third, we will develop in concert with end-users an original, generic and user-friendly software (in the R statistical platform) to assist biologists in investigating communities’ structure and dynamics through multispecies demography modeling (WP3). Overall, we will adopt a multidisciplinary approach in which important questions in community ecology will be addressed with robust and modern methods from demography, statistics and computing science.