What is the relative importance of physical, biological environment and geographic distance in shaping medium and large fauna assemblages in lowland Amazonia?

Understanding the response of communities to spatially heterogeneous environmental conditions is an important challenge for ecologists. Whereas broad-scale Amazonian forest types have been shown to influence the structure of the communities of mediumto large-sized vertebrates, their natural heterogeneity within the terra firme rainforests remains poorly investigated. Here we question the drivers of the diversity and composition of medium and large fauna assemblages from a species-neutral, functional and phylogenetic perspective. In this study, we disentangled the effects of various physical, biological and spatial covariates on the composition and diversity of 21 communities of 19 medium- and large-sized vertebrates in neotropical terra firme rainforests, French Guiana (~84,000 km²). We sampled each local vertebrates community using standardized line transects (sampling effort of ~5,000 km). We estimated species densities using distance sampling method taking into account temporary emigration and imperfect detection. Raw population density data were used to analyse species-neutral assemblages. Functional compositions and diversities were estimated from 9 morphological and behavioral traits while phylogenetic ones were measured from discrepancies between taxonomic levels (from species to classes). Physical environmental conditions were extracted from remote sensing data (e.g. mean landforms slope, mean elevation). Biological environmental conditions were estimated in the field (e.g. biomass, dominant tree families). Finally, geographic distances between sites were calculated to assess spatial effects on the structure of communities. We implemented variation partitioning to determine the relative importance of each covariate in shaping fauna assemblages. At this spatial extent, we can hypothesize that biological conditions explain better composition and diversities than physical conditions because of their potentially direct influences on fauna. In addition, these res