LAUSR

Species diversity can be a result of environmental and spatial constrains that act at small and large spatial scales. An important question in community ecology is to know the contribution of each one in studies with multiple spatial scales. We examined aquatic insect assemblages in small streams from the Atlantic Forest in a mainland-island scenario, with the aim of measuring which variables explain the β-diversity of insects at three spatial scales (streams, ecoregions, mainland-island). We sampled 20 streams across four ecoregions, two on the mainland and two on the island. Spatial distribution of streams was hierarchical and ecoregions were isolated. The β-diversity decreased with increasing spatial scale, where higher values were found among streams and not among ecoregions or mainland-island. Our results indicate that the contribution of environmental and spatial predictors to the β-diversity of aquatic insect varies according to the scale of observation. Environmental variables of water and riparian forest had a greater effect on β-diversity among stream sites, while spatial and landscape (physical barriers) variables seem to be key factors at larger scales (ecoregions and mainland-island, respectively), which can prevent dispersal. Our study shows that local environmental heterogeneity had a great importance for maintaining regional diversity of aquatic insects.