Homogenization dynamics of the fish assemblages in Neotropical reservoirs: comparing the roles of introduced species and their vectors

Non-native species introduced into reservoirs cause major changes in biodiversity, resulting in spatial and temporal biotic homogenization and/or differentiation. We used a sampling standardized temporally and spatially in reservoirs of basins located in the Neotropics, the Coastal, Igua double dagger u, and Upper Parana basins. Our analyses were conducted at the interbasin and intrabasin scales, aimed at: (i) identifying the non-native species and their major vectors of introductions, (ii) assessing temporal and spatial changes in the fish assemblages, and (iii) evaluating temporal changes in the beta diversity of the basins/reservoirs. The spatial occupation of non-native species was variable, with Tilapia rendalli, Cyprinus carpio and Oreochromis niloticus the most frequently introduced species. This highlights aquaculture as the main vector of invasives on a large spatial scale. The percentage of non-native species at the interbasin and intrabasin scales increased over time. Temporal comparisons of the fishes support the hypothesis that biotic homogenization occurred at the interbasin scale, whereas the biotic differentiation was observed at the intrabasin scale. Beta diversity decreased over time at the interbasin and intrabasin scales, with decrease in species richness serving as the variable that best explained changes in biological diversity. There was no relation between beta diversity and time for the Igua double dagger u.