Geographic distance and temperature explain Passeriformes beta diversity in Amazon

Beta diversity can be measured as the change in species composition over space and it can be decomposed into the turnover (species replacement) and nestedness (species loss) components. The patterns in beta diversity can be explained by stochastic (neutral) and deterministic (niche) processes. In this study, we partitioned the beta diversity of Amazonian Passeriformes into the turnover and nestedness components and verified the association of these components with climatic differences, geographical distance, and the presence of major rivers. We divided Amazonia into 549 grid cells (1º of latitude and longitude) and obtained presence-absence data for each cell from previously published studies (BirdLife). Climatic data (mean annual temperature and precipitation) were obtained from remote sensing. Beta diversity was measured by the Jaccard dissimilarity index between pairs of cells. The association between environmental variables and the components of beta diversity was evaluated using multiple regression analysis of matrices. Changes in species similarity between sites (beta diversity) is more strongly associated with species turnover (bSIM =0.99) than nestedness (bSNE=0.01). The turnover in species composition is strongly associated with geographic distance (R2: 0.48), mean annual temperature (R2: 0.31), and the presence of the Amazon river. Our results suggest that rivers and temperature determine the distribution of birds in the Amazonian forest. In areas with no clear barriers for bird dispersal, the environment is strongly associated with changes in species composition. Regional characteristics may be determining the beta diversity of birds in Amazonia, coupled with the ecological characteristics of individual species.