Relative roles of environmental and spatial constraints in assemblages of Chironomidae (Diptera) in Amazonian floodplain streams

We studied the diversity and abundance of Chironomidae assemblages according to the metacommunity framework, aiming to disentangle environmental and dispersal-driven processes in Amazonian streams. Because of the high heterogeneity in Amazonian landscapes and daily flood regimes connecting stream network, we tested if dispersal limitations play a smaller role than environmental variation in explaining variation in community composition. We investigated how community structure and species richness were affected by environmental variables, and how differences in geographic distance between streams best explain metacommunity patterns. We found remarkable environmental effects (i.e., species sorting) and low spatial contribution (i.e., dispersal limitation) on the metacommunity structure. Canopy density mid-stream, percentage of wood debris, and wetted width in streams were the main environmental factors for explaining community structure. Overall, we found only effects of broad-scale patterns in metacommunity structure explained by spatial filters. Community structure was most explained by Asymmetric eigenvector maps representing directional dispersion effects along the basin-scale and less explained by Moran's eigenvectors maps suggesting that overland dispersal limitation has a weak role in ruling the assemblages. Our results support that without dispersal limitation, the combination of species sorting and mass effects is the main pattern structuring chironomid metacommunities between Amazonian floodplain streams.