Changing taxonomic and functional β-diversity of cladoceran communities in Northeastern and South Brazil

Abstract

Disturbances caused by both natural and anthropogenic forces can drive changes in alpha and beta taxonomic diversity and be accompanied by losses or gains in freshwater ecosystem function (e.g., secondary productivity and rate of decomposition). In this study, we tested the hypothesis that increases in cladoceran (microcrustaceans) taxonomic beta diversity in highly impacted environments lead to functional simplification and homogenization of community trait composition. This was accomplished by comparing a reference group of low-impact waterbodies (lakes and reservoirs) to high-impact waterbodies located in four regions of northeastern and south Brazil. Functional composition of cladoceran communities was inferred using a suite of morphological, physiological, behavioral, and life-history traits. Differences in taxonomic and functional community composition were tested using univariate and multivariate statistics. Taxonomic beta diversity and functional richness differed significantly between the reference (low-impact) and high-impact waterbodies, where high-impact environments showed higher taxonomic and functional beta diversity and lower functional richness. By contrast, we found functional homogenization of cladoceran communities in just one out of the four regions. Last, we propose that disturbances can affect traits locally in communities, making them rarer until they are lost, by promoting functional simplification. When disturbances are persistent, they lead to functional and taxonomic homogenization.