The relative importance of spatial and environmental processes in the assembly of larval Chironomidae (Insecta, Diptera) communities along a transition landscape in southern Brazilian streams

Abstract

Metacommunity structure of stream invertebrates is contingent on complex interplays between species dispersal ability, spatial extent and watershed environmental specificities. Previous studies showed that high diversity of Chironomidae (Insecta, Diptera) is observed in southern Brazilian montane streams, although the knowledge of the processes driving such high diversity is poorly comprehended. In this study, we evaluated the relative contribution of environmental (in-stream and landscape) and spatial drivers to the metacommunity structure of larval Chironomidae in a watershed (N = 40 stream reaches) running across a forest–grassland transition landscape in southern Brazil. Overall, 51 taxa were recorded in the study region. We found similar contributions of the environmental (in-stream and landscape) and spatial (broad- and fine-scale spatial drivers) fractions to the metacommunity structure of larval Chironomidae. Our results suggest that environmental processes likely associated with the elevation and stream longitudinal gradients predominated in the assembly of the metacommunity structure of larval Chironomidae. Additionally, mass effects (exchange of individuals via dispersal) possibly associated with the short-range drift or flight and the contact zone between the fauna from each biome also accounted for the observed pattern. Finally, dispersal limitation associated with the spatial extent and the topographic heterogeneity of the study region likely played a minor role in the assembly of Chironomidae metacommunity structure.