Taxonomic and functional homogenisation of zooplankton after river damming in Central Brazil

Abstract

1. Dams on large rivers alter hydrodynamics, reduce seasonal variability and environmental heterogeneity, and have significant effects on river ecology. They produce less diverse environments and alter the community composition. Knowledge about the effects of dams on functional aspects of zooplankton communities is scarce. Thus, our main goal was to investigate how the zooplankton community of the Tocantins River in central Brazil changed after the implementation of the Estreito hydroelectric power plant dam. We explored the relationships of taxonomic and functional beta diversity in the zooplankton community, with the seasonality, flooding river phases and limnological variables. 2. To answer our goals, we collected water samples 1 year before plant construction and 5 months after dam enclosure. To investigate how the environment changed after river damming, we conducted a principal component analysis. We calculated taxonomic and functional beta diversity using the Jaccard pairwise dissimilarity index for presence–absence data. To identify which functional traits were associated with each river phase and season, we firstly calculated the community weighted mean (CWM) for each trait. Secondly, we partitioned beta diversity into turnover and nestedness components. To investigate patterns of taxonomic and functional beta diversity and its turnover and nestedness components, we additionally used a series of six linear mixed models. 3. Our results indicated that the limnological characteristics of the river changed after damming. Taxonomic and functional turnover was higher during the pre-inundation phase, and this phase also showed greater limnological heterogeneity in comparison to the post-inundation phase. We observed a strong seasonal dynamic in taxonomic turnover, with high turnover during the dry season. However, these seasonal dynamics disappeared after river damming. We demonstrated that the patterns of taxonomic and functional beta diversities were influenced by limnological variables and seasonal dynamics, which resulted in reduced variability in both species composition and functional characteristics after the implementation of the reservoir. 4. This study emphasises the importance of variations in annual flow regimes in lotic ecosystems. We also showed an association between environmental heterogeneity patterns the high taxonomic and functional diversity of zooplankton communities.

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