Relative influences of environmental and spatial factors on stream fish assemblages in Brazilian Atlantic rainforest

Understanding the role of local and spatial factors in the structuring of aquatic communities is a goal in ecology. The hierarchical structure of stream systems provides opportunities to test the hypothesis that fish assemblages that are more isolated in headwaters are structured by local and/or regional variables. Fishes and abiotic data were collected in 18 stream reaches from two hydrographic basins in the Brazilian Atlantic rainforest. The variance of species composition was partitioned into fractions explained by environmental and spatial factors. The pure environmental fraction explained ≈17% of variance and was represented by regional, habitat availability/heterogeneity and perturbation gradient. The pure spatial fraction explained ≈15% of the individual fraction. Environmental data revealed a species sorting process, and the spatial effect might be a result of different dispersal routes that fish performed during the formation of the hydrographic basins, actual land use and water resources management. The importance of maintaining connectivity in these systems was emphasised because it cannot be guaranteed that the dispersion ability of species is still occurring under current land use change.