Drivers of macroinvertebrate metacommunity structure in Tierra del Fuego rivers

Among the different mechanisms that shape metacommunity structure, species sorting and mass effects are the most studied and reported mechanisms. Species sorting is related to environmental filtering, while mass effects are related to high dispersal between communities, which ultimately overrides environmental controls. In this paper, we aimed at studying metacommunity patterns of stream macroinvertebrates on Tierra del Fuego Island at different spatial scales (province, ecoregion and catchment) and at different positions along the river network (upstream, mid-stream and downstream segments) to understand the mechanisms driving metacommunity structure. For this purpose, we used complementary approaches based on the analysis of beta diversity index as well as its turnover and nestedness components, which are associated with the two main underlying mechanisms of metacommunity structure (species sorting and mass effect). Our results indicate that species sorting is the preponderant mechanism structuring these macroinvertebrate metacommunities at larger spatial scales, with an increased importance of mass effects at smaller scales (e.g., catchment). Metacommunities at different positions on the river network exhibit similar total beta diversity values, turnover and nestedness components. On the other hand, turnover and total beta diversity increased with spatial extent, while nestedness remained constant. Those results suggest that at the catchment scale and along the longitudinal axis of the rivers other mechanisms, like randomness and species dispersal, are more important in shaping the macroinvertebrate metacommunity.