Contrasting continental patterns and drivers of taxonomic and functional turnover among fish assemblages across Brazilian reservoirs

In this paper, we investigated composition and trait turnover among fish assemblages in reservoirs distributed across major Brazilian basins, in order to contrast taxonomic and functional turnover and to investigate their respective drivers. We investigated the hypothesis that reservoir assemblages present, on a continental scale, divergent species compositions but with a similar set of traits. Species lists and functional traits were compiled from 79 reservoirs located in the Amazon, São Francisco, Paraná and Atlantic basins. We observed considerable variation in species and trait composition among reservoirs, with higher intra-basin similarity. Taxonomic turnover ranged between 0 and 1 (0.44 ± 0.22 SD), and functional turnover between 0 and 0.91 (0.37 ± 0.19); functional turnover correlated positively with taxonomic turnover, but showed lower values. Observed functional turnover values did not differ from null expectations, indicating lack of functional convergence. We detected significant effects of basin, longitude, latitude and elevation on turnover values, and the presence of non-native species was associated with either homogenization or differentiation patterns. Our results indicated that fish composition is heterogeneous among impoundments, providing little support to the hypothesis that reservoir assemblages are homogenized on a continental scale. Species and trait composition probably respond to multiple spatial, environmental and biogeographic factors.