Abstract

The biodiversity of assemblages that experience the introduction and extinction of species may lead to responses in two important facets: The taxonomic and functional diversity. The way in which these facets are associated may reveal important implications and consequences for the conservation of those assemblages. Considering the critical situation of freshwater fishes in continental Chile (30 degrees - 56 degrees S), we analyzed how the taxonomic (TD beta) and functional (FD beta) facets of beta-diversity, and their components of turnover and nestedness, are associated. We evaluated changes in beta-diversity (Delta TD beta and Delta FD beta), turnover (Delta TDtur and Delta FDtur), and nestedness (Delta TDnes and Delta FDnes) in 20 fish assemblages from their historical (pre-European) to current composition. We also simulated future trends of these changes, assuming that native species with conservation issues would become extinct. Our results show that the fish assemblages studied are in a process of loss of beta-diversity, both in taxonomic and functional facets (Delta TD beta = -3.9%; Delta FD beta = -30.4%); also, that these facets are positively correlated in the assemblages studied (r = 0.617; P < 0.05). Both components showed by loss in nestedness (Delta TDnes = -36.9%; Delta FDnes = -60.9%) but gain in turnover (Delta TDtur = 9.2%; Delta FDtur = 12.3%). The functional beta-diversity decreased more than the taxonomic (Delta FD beta > Delta TD beta), which was caused chiefly by six exotic species of Salmonidae, whose geographical spread was wider and that at the same time shared several morpho-functional traits. Our forecasts, assuming an intensification in the extinction of Endangered and Vulnerable native species, indicate that the process of homogenization will continue, though at a lower rate. Our study shows that the freshwater ichthyofauna of continental Chile is undergoing biotic homogenization, and that this process involves the facets of taxonomic and functional beta-diversity, which are show high correlation between historical and current compositions. Both facets show that process is influenced by nestedness, and while turnover contributes to differentiation (both taxonomic and functional), its importance is overshadowed by nestedness.