CONICET | Buscador de Institutos y Recursos Humanos

Among the different mechanisms that shape metacommunity structure, species sorting and mass effects are the moststudied and often reported mechanisms. Species sorting it?s related with environmental filtering while mass effects isrelated with high dispersion between communities, that ultimately overrides environmental control. In this paper weaimed at studying metacommunity patterns of stream invertebrates in Tierra del Fuego Island at different spatial scales(province, ecoregion and catchment) and at different positions along the river network, (upstream, mid-stream anddownstream segments) in order to understand the mechanisms driving metacommunity structure. For this purpose, weused complementary approaches based on the analysis of beta diversity index as well as its turnover and nestednesscomponents, which are associated with the two main underlying mechanisms of metacommunity structure (speciessorting and mass effect). Our results indicate that species sorting is the preponderant mechanism structuringmacroinvertebrate metacommunities at larger spatial scales, with an increased importance of mass effects at smallerscales (e.g. catchment). Metacommunities at different positions on the river network exhibit similar values of total betadiversity, turnover and nestedness components. On the other hand, turnover and total beta diversity increased withspatial extent, while nestedness remained constant. Those results suggest that at the catchment scale and along thelongitudinal axis of the rivers other mechanisms, like randomness and species dispersal, are more important inshaping the macroinvertebrate metacommunity.