On the relative importance of space and environment in farmland bird community assembly

International audience; The relative contribution of ecological processes in shaping metacommunity dynamics inheavily managed landscapes is still unclear. Here we used two complementary approachesto disentangle the role of environment and spatial effect in farmland bird community assemblyin an intensive agro-ecosystem. We hypothesized that the interaction between habitatpatches and dispersal should play a major role in such unstable and unpredictable environments.First, we used a metacommunity patterns analysis to characterize species co-occurrencesand identify the main drivers of community assembly; secondly, variation partitioningwas used to disentangle environmental and geographical factors (such as dispersal limitation)on community structure and composition. We used high spatial resolution data on birdcommunity structure and composition distributed among 260 plots in an agricultural landscape.Species were partitioned into functional classes, and point count stations were classifiedaccording to landscape characteristics before applying metacommunity andpartitioning analyses within each. Overall we could explain around 20% of the variance inspecies composition in our system, revealing that stochasticity remains very important atthis scale. However, this proportion varies depending on the scale of analysis, and revealspotentially important contributions of environmental filtering and dispersal. These conclusionsare further reinforced when the analysis was deconstructed by bird functional classesor by landscape habitat classes, underlining trait-related filters, thus reinforcing the idea thatwooded areas in these agroecosystems may represent important sources for a specificgroup of bird species. Our analysis shows that deconstructing the species assemblages intoseparate functional groups and types of landscapes, along with a combination of analysisstrategies, can help in understanding the mechanisms driving community assembly.