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	My work focuses on dynamical and multi scale approaches of the relationships between organisms and their environment. My main activities aim to describe and understand the effects of climate change on aquatic ecosystems. A first part thus deals with analysis of existing biological and environmental time series. More generally, a second part of my work aim to a better understanding of ecological temporal processes. If more theoretical and not directly related to the global warming, this second part could help identifying ecological processes implied in the observed responses of ecosystems to climate change. 1. Observed effects of climate change on community structures:   Studies addressing the effect of global warming on freshwater ecosystems are still scares and mainly focused on lakes. Part of my work consists in studying the influence of climate change on fish and invertebrates community structures in large rivers. • Effects of the gradual atmospheric warming:   Using multivariate analysis and statistical methods appropriate for autocorrelated time series, I have shown that climate change has significantly influenced the fish and invertebrate community structures of the Upper Rhône River (Daufresne et al. 2004). To expand this study, I then attempted to compare such effect across 7 fish communities of the main French large rivers, undergoing different kinds of non-climatic anthropogenic pressures. These analyses involved species traits and combine (to my knowledge for the first time) both  meta-analysis and temporal autocorrelations (Daufresne and Boët submitted). We showed that, despite effects of non-climatic pressures, fish community structures were globally strongly influenced by climate change. • Effects of extreme climatic events:   Beside the effects of the atmospheric gradual warming, I also focused on effects of extreme climatic events, and especially of the European 2003 heatwave. We observed a deep effect of the heatwave on mollusc community structure of the Saône River (Mouthon and Daufresne 2006). Because occurrence of such event should increase (consequently to climate change), our study revealed that, during this century, more than half the mollusc species currently inhabiting the potamic area of large rivers are directly threatened with disappearance. A study, performed currently at the species level, should enable a better understanding of such processes (Mouthon and Daufresne submitted).   A recent study (Daufresne et al. 2007) underlined the cumulative effects of gradual warming and extreme climatic event on macroinvertebrate communities of the Rhône at 9 study sites. As already observed, we highlighted gradual changes in community structures. However, our analyses stressed the important effects of hydro-climatic events on community dynamics. The most important changes in community structures was due to the 2003 heatwave. More specifically, we clearly documented that all strong hydro-climatic events (floods, heatwave) systematically led to the development of eury-tolerant and invasive taxa. Contrary to expectations, we did not observe any sign of recovery and the relative sensitivity of communities to extreme hydro-climatic events seemed to increase with time. As a consequence, predicting changes in the dynamics of communities seem difficult in the context of global warming. Beside a gradual change in community structures, we emphasized that even slight hydro-climatic event could produce drastic shift in macroinvertebrate communities. 2. Dynamical ecological processes: • Limitation, regulation and fluctuations of populations:   The main purpose of this work was to understand non-consistent effects of environment variables on population dynamics at the inter-annual vs long-term scale. We previously showed (Daufresne et al. 2004) that such pattern has been observed for the relationship between dace population and temperature during reproduction. I have chosen to work on brown trout because the ecology of this species is particularly well documented.   We developed a simple matrix population dynamics model to analyse the relative influence of biotic and abiotic factors on population dynamics (Daufresne and Renault 2006). We showed that density-dependent (regulation) and density-independent processes could act together to control and optimised population size (limitation) and stability of equilibrium. We also show that endogenous regulatory processes may often be invisible when analysing abundance fluctuations at the inter-annual scale. Our work underlines the difficulties to identify long-term effects of environmental constraints (e.g. climate change) on population dynamics analysing abundance inter-annual fluctuations. • Limitation, regulation and fluctuations of populations:   A third part of my activities deals with temporal stability of communities. In collaboration with D.O. Hessen (University of Oslo), I am currently trying to identify factors controlling temporal stability of phytoplankton and zooplankton communities in Norwegian lakes. Using PLS regressions, we showed that temporal stability of phytoplankton communities was negatively related to the total phosphorus concentrations. Temporal stability of zooplankton communities was positively related to specific richness, habitat availability and temporal stability of phytoplankton communities and negatively related to total phytoplankton abundance.   The ultimate aim of this work is to identify the factors controlling the relative responses of communities to climate change. Using large data set, meta-analysis and time-series analysis methods, it sounds interesting, in a second step, to related the factors stabilising temporal variability of community structures to the intensity of their changes due to climate change. 3. Transversal activities:   My statistical background allowed me to collaborate on several other transversal subjects. Most of them dealt with dynamical patterns but are not closely related to long-term changes (see list of publication). I have in particular worked on relationships between individual behaviours and timing of environmental constraints (by an experimental approach, see Daufresne et al. 2005) or on the development of goodness of fit (gof) statistics in order to improve the biological accuracy of the population dynamics model described above. All these activities allowed me to improve my knowledge on dynamical ecological patterns and to develop new statistical abilities. TOP