How are local fish communities structured in Brazilian semiarid headwater streams?

Environmental and spatial factors are known as the main determinants of community variation in aquatic organisms. However, historical factors may interact with local processes to regulate community structure patterns. Here we compared historical, environmental, and spatial factors in a multi-scale approach in order to identify the main drivers structuring species composition and functional diversity of fish communities in forest enclaves across three hydrographic basins in semiarid Brazil Caatinga biome. We initially modeled spatial structure within each basin using asymmetric eigenvector maps (AEM). We then partitioned the explanation of the variation in local community structure into three groups of predictor variables: (1) environmental variables, (2) spatial variables, and (3) phylogenetic history. Biogeographical bias was assessed using a basin identity matrix as covariable. The combination of 1, 2, and 3 explained the variation in species composition, while pure spatial, phylogenetic, and environmental components explained the distribution of functional groups and their nested patterns. Our findings confirmed the importance of phylogenetic history, as well as the usefulness of robust methods in community studies in refining explanations of the processes determining variation in species composition and functional groups.