Ecosytem functionning at the crossroad of biogeography and community ecology

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Ecologists have always been fascinated by the spatial distribution of biodiversity. Temperature impacts directly many ecosystem processes over large biogeographical gradients because it affects biological rates. Climate is also an essential driver of many species ranges and ecological interactions. At the crossroad between these facts is however found a fundamental, and still unanswered, question: to what extent the distribution of biodiversity, and the community ecology taking place, is influencing the global distribution of ecosystem functioning? The long-term objective of my research program is to develop theory to understand and predict biodiversity distribution and ecosystem functioning at biogeographical spatial scales. More specifically, I will investigate the hypothesis that the spatial variation of the architecture of ecological interactions is constraining ecosystem productivity at the biogeographical scale, in synergy with the direct effect of temperature on biological rates. My specific objectives are: i) develop a mathematical formalism to represent the architecture of metaecosystem interaction networks; ii) synthesize the complexity of metaecosystems with analysis of their dimensionality; iii) formalize and test quantitative theory of temperature-dependence of trophic regulation. ******I will integrate different methodological approaches to reach my objectives, from mathematical modeling to experiments and field observations. In project 1, I will reconstruct the network of direct and indirect ecological interactions across the Arctic. I will conduct field sampling at sites spread across the gradient to document plant-herbivore, plant-pollinator and predator-prey interactions, which I will integrate with knowledge of spatial exchanges by migration and foraging of animals. In project 2, I will investigate the dimensionality of metaecosystems. I will quantify the number of latent variables required to describe the variation in the structure of willows-gallers-parasitoids networks across northern Europe. In project 3, I will develop and test a quantitative theory of temperature-dependence of trophic regulation. I will use the microbial food web inhabiting the leaves of the purple pitcher plants to parameterize the model and conduct experiments testing its quantitative predictions. The strength of this program is based upon the integration of biogeography, community ecology and ecosystem ecology. The formalism I will develop will bring the field beyond the simplistic view of 'networks of networks'. Metaecosystems are among the most complex ecological structures because they integrate space, time and interactions and I will quantify their dimensions to challenge the view that community ecology is a mess. Finally, the theory I develop will be critical to understand the joint effects of climate change and biodiversity loss on ecosystem functioning.