Frontiers of Biogeography

From a literature review, we constructed a database comprising >1000 freshwater insect species (especially Odonata, Coleoptera, Trichoptera, Ephemeroptera; OCTE) in 26 Geographical Caribbean Units (GCU) and quantified local filtering (climate heterogeneity, annual rainfall, annual temperature), geography (area, distance from the mainland) and emergence age as a proxy for island ontogeny. We investigated the relative role of these variables on the species richness, endemism and composition of the units using island species-area relationship (ISAR), generalised linear modelling (GLM) and nonmetric multidimensional scaling (NMDS). In addition, we analysed the spatial patterns of species richness and composition using Moran’s I index. ISAR generally demonstrated one or two thresholds and continuous or discontinuous responses according to OCTE groups. A small island effect could be detected for Trichoptera and Ephemeroptera richness, whereas Odonata and Coleoptera only demonstrated differences in slope between smaller and larger GCUs. Area, climate heterogeneity, maximal rainfall and distance from mainland were major drivers of species composition in GCUs, whereas local climate variables were of main importance for the endemism rate. Due to the potential complexity of the Caribbean island ontogeny, middle-stage islands had an expected higher freshwater invertebrate richness than younger ones but an unexpected lower richness compared to older islands. Finally, the degree of colonization of islands was linked to the dispersal ability of species, with Odonata and Coleoptera having larger distribution ranges than Trichoptera and Ephemeroptera, which were more restricted by their comparatively narrow ecological niches. The high endemism (>60%) found in the Caribbean freshwaters calls for more conservation effort in managing these highly threatened freshwater environments.