Phylogenetic diversity of stream fishes reflects habitat variation, while functional diversity responds to human impacts

Abstract Human‐induced land‐use changes are a major driver of biodiversity loss in Amazonian freshwater ecosystems, while natural variation among aquatic environments also shapes community structure. We assessed how local habitat variables and land‐use impacts influence the functional and phylogenetic diversity of stream fish assemblages across 71 Amazonian streams. We quantified indices of functional diversity (functional richness, evenness, and divergence) and phylogenetic diversity (phylogenetic richness, mean phylogenetic distance, and nearest taxon distance), and evaluated their associations with environmental variables using generalized linear models. Our results revealed that human impacts in riparian zones were positively associated with functional richness but negatively associated with functional divergence, suggesting the addition of functionally similar species in disturbed environments. In contrast, phylogenetic diversity responded primarily to habitat heterogeneity: coarse litter was negatively associated with phylogenetic diversity, whereas undercut banks were positively associated with it, indicating that structural complexity supports phylogenetically diverse assemblages. Our findings emphasize the importance of habitat heterogeneity and riparian integrity to conserve evolutionary history and ecological functions in Amazonian streams.