Unraveling patterns of taxonomic and functional alpha and beta diversity of fish assemblages in reservoirs: the role of spatial gradients, environment structure, urbanization, and non-native species.

Abstract

Rivers affected by dams often exhibit predictable gradients and show reduced taxonomic and functional diversity compared to natural systems, with a dominance of generalist and invasive species due to environmental modifications. Long reservoirs usually present longitudinal zonation, with the presence of fluvial, transitional, and lacustrine zones, and reservoir fish are frequently found in regions of high environmental heterogeneity, particularly littoral and vegetated areas. Thus, examining patterns of fish diversity in reservoir habitat while considering different environmental factors, such as longitudinal and transversal gradients, along with landscape changes, the presence of non-native species, and habitat structure, can help understand anthropogenic impacts on these systems. Therefore, this thesis aimed to evaluate the diversity of fish assemblages in face of spatial gradients, biotic pressures (non-native species), and anthropogenic influence, using the Itaipu Reservoir as a case study. The main aims were to analyze the taxonomic and functional alpha and beta diversity patterns of fish assemblages along the longitudinal gradient of the reservoir (fluvial, transitional, and lacustrine zones), considering the different habitats, and to evaluate the environmental factors (habitat structure and urbanization) and biotic factors (richness of native and non-native species) influencing the beta diversity components of fish assemblages in the shoreline areas of the reservoir. In summary, our results suggest that the taxonomic and functional alpha and beta diversity of fish assemblages are related to the longitudinal gradient. However, the differences were not remarkable, which may be attributed to the homogenization of the fish fauna in our study area, considering both habitats evaluated. Moreover, the taxonomic and functional beta diversity of fish in the reservoir shorelines are influenced by environmental factors, such as habitat structure and urbanization, which create an environmental gradient, and by biotic factors, such as the richness of native and non-native species. In conclusion, comprehending the spatial organization of fish communities in reservoirs, across different habitats and under the influence of different biotic and environmental factors, improves knowledge on the effects of reservoirs on aquatic organisms, considering their multiple uses.