Biodiversity as an insurAnce against environmental CHange – BACH

In a world increasingly perturbed by human activities it is now urgent to evaluate the potential role of biodiversity on shaping ecosystems properties and services. To this end it is necessary to both understand the mechanisms that drive species richness dynamics and their relationships with ecosystem processes. In this context, the biological insurance hypothesis proposes that biodiversity can buffer against environmental fluctuations. This hypothesis has received a great deal of attention the last few years because it is directly linked to the vulnerability of biological system to global change mediated by human activities (fragmentation, homogenization, environmental variation). The spatial and temporal insurance hypothesis proposes that species diversity plays the role of an 'insurance' against environmental fluctuations given that species are functionally complementary in space and/or time and that ecological systems are sufficiently connected. These results are fundamental because they emphasize an effect of species diversity that could not be detected in classical approaches which mostly consider the local scale. Moreover, they illustrate that any change in the spatial structure of the landscape (habitat destruction, fragmentation, isolation, etc.) could have very strong consequences on the stability and levels of ecosystem functioning at both local and regional scales. While this theory has now been well developed in community ecology, it lacks of experimental validations and needs to integrate some elements of evolutionary ecology. Our project is built around these limitations and will combine theoretical and experimental approaches to better understand the relationship between species richness and ecosystem functioning based on both current knowledge in community ecology and evolutionary biology. This work is a part of the main research program initiated by Nicolas Mouquet since he has been recruited at the CNRS four years ago. Some of it has been partly funded by the INSU through the EC2CO proposal until 2008. This preliminary work has allowed Nicolas Mouquet to build-up a young team of collaborators around his project and to start up a new microbiology lab. The originality of this work has been acknowledged through a recent paper published in Nature on the adaptive radiation within a metacommunity. The 'ANR jeune chercheur 'seems now the most appropriate framework to push this program and ideas to a higher level. We will develop two main axes: Ecological (axe I) and Evolutionary (axe II) insurance hypotheses that will both combine theoretical and experimental approaches. The experimental part of the first axe will use marine bacterial communities to test in the field and in the lab the main predictions of the insurance hypothesis. Its theoretical part will develop further the ecological insurance hypothesis integrating more realistic landscapes and spatial food web theory. The experimental part of the axe II will use the bacteria Pseudomonas fluorescence SBW25 in the lab (microcosms) to study the evolution of niche width in a temporally variable environment and the relative importance of ecological vs. evolutionary insurance effects. The theoretical part of the second axe will develop the basis of the evolutionary insurance, by integrating current knowledge on niche evolution. Our work is by nature multidisciplinary mixing community and ecosystem ecology, evolutionary biology, microbiology and modelling of complex systems. We have chosen to work with bacteria because they offer the unique opportunity to obtain rapid ecological and evolutionary responses using experimental designs that fulfill the assumptions of theoretical models. They are easy to grow in the lab, have rapid generation time, high population size and can be grown in small containers that allow the design of complex and robust experimental protocols. They have become central in the last 10 years to study experimentally the evolution of species diversity. Modern techniques used in microbiology are very precise, affordable and allow field measures of the dynamics of species richness that was not reachable only five years ago. These new techniques make it possible to explore experimentally areas where theory has been pushed far but where experimental approaches are still scant. Moreover bacteria mediate some of the most important aspects of ecosystem function, including nutrient cycling, the degradation of detritic organic matter and its conversion into living biomass, and the regulation of the major biogeochemical cycles. This makes of their implication in an insurance effect a central question in understanding and forecasting the consequences of biosphere modifications by human activities.