The effect of riverine networks on fish β-diversity patterns in a Neotropical system

We investigated how the riverine network influences taxonomic and functional beta diversity patterns of fish assemblages in the mainstem/headwater (lateral) and upstream/downstream (longitudinal) gradients in a Neotropical river system. We investigated the following questions: which component (turnover or nestedness) explains taxonomic and functional beta diversity in both gradients? Is this component a consistent pattern for different lateral sections of the river basin? Is this component influenced by the spatial extent? Finally, how are taxonomic and functional beta diversity structured by space and environment along the longitudinal gradient? Taxonomic and functional turnover were the main patterns found for the lateral gradient and they were consistent for all lateral sections considered. Taxonomic and functional turnover were also the main patterns for the longitudinal gradient, increasing with the spatial extent increase and being structured by space and spatially structured environments. Our study demonstrates that the dendritic nature of riverine systems constrains species and traits occurrence along lateral and longitudinal gradients in a Neotropical region, generating taxonomic and functional turnover patterns due to the influence of space and spatially structured environments on niche- and dispersal-based processes. These results show that Neotropical riverine systems conservation must go beyond traditional approaches and consider the metacommunity perspective.