Effects of dams decrease zooplankton functional -diversity in river-associated lakes

In river-floodplain systems, the construction of dams causes environmental changes in the natural dynamics of rivers and the associated wetlands, which can affect both the taxonomic and functional composition of communities, and, consequently, ecosystem functioning. We evaluated zooplankton taxonomic and functional -diversity in sets of lakes associated with a preserved and a dammed river in a Neotropical floodplain. We expected that both -diversity measures would be lower in lakes associated with a dammed river than in lakes associated with a preserved river. -Diversity was partitioned into turnover and nestedness components, through multiple-site dissimilarity measures, and compared with expected null models. We expected that nestedness would be more important for both the -diversity measures in lakes associated with the dammed river, whereas species and trait turnover would be more important in lakes associated with the preserved river. Functional -diversity was higher among lakes of the preserved river than of the dammed river, while taxonomic -diversity was not different between the rivers. Contributions of turnover and nestedness components were similar in the preserved river, whereas that of nestedness was higher in the dammed river, revealing the loss of extreme trait combinations from the functional space. Comparisons between observed and expected -diversity revealed a higher trait turnover than would be expected by species turnover in the preserved river, and no differences from the null models were observed in lakes associated with the dammed river. Our results suggest that dissimilarity in trait composition is influenced more by environmental changes associated with river damming than by dissimilarity in species composition such that a functional homogenisation occurs without a change in taxonomic -diversity. We propose the maintenance of preserved tributaries in floodplains, which sustain environmental heterogeneity, primarily if the nearby environments are already dammed. Furthermore, we reinforce the necessity of a pluralistic approach, considering both taxonomic and functional aspects of biodiversity in ecosystem management.