Human impacts alter the distribution of fish functional diversity in Neotropical stream system

Evaluation of traits and functional diversity make assessments more robust when determining the nature and strength of the relationship between species and ecosystem processes. We investigated how anthropic interference and physical and limnological characteristics of streams changed fish functional trait distribution and their functional diversity in Neotropical streams located in Southern Brazil, encompassing Parana, Paranapanema, Ivai, and Pirapo river basins. We tested the hypotheses (a) that streams with very low human pressure show higher values of functional diversity due to the great variety of habitats and food resources; (b) streams with higher human pressure and more deforested are more related to fish functional traits as body morphologies indicative of weaker swimming ability and scraping feed morphology. We found that current velocity and stream width were correlated with compression and depression indices of the ventral region of the animals. Faster-flow environments favored higher values of relative height of the caudal peduncle, relative head width, and relative mouth height values. These functional traits relate to habitat use and the size of consumed food. Altogether, these findings indicate possible partitioning of resources that would enable the co-occurrence of species. Our results showed that human impacts influenced functional diversity and functional trait distribution. Urban land use and high conductivity were correlated with detritivorous species and species with internal reproduction. Poecilia reticulata dominated urban streams. We argue that the conservation of fish diversity in Neotropical streams requires orderly land use and occupation to avoid reducing species and functional diversity, and hence ecosystem function. in Portuguese is available with online material.