The likely effects of river impoundment on beta-diversity of a floodplain zooplankton metacommunity

Using a long-term dataset, we tested whether beta diversity of the zooplankton community in the Upper Paraná River floodplain increases during periods of high environmental heterogeneity and productivity and decreases with increases in water level (when there is higher connectivity between sites). We detected temporal trends of increasing beta diversity. A temporal decrease in species occupancy was more frequent than a temporal increase. Our results do not support a generalized association between beta diversity and environmental heterogeneity or productivity. Water level variation was an important explanatory variable only for rotifers and in the opposite direction expected. Taken as whole, our results suggest that we are far from a comprehensive understanding of the processes underlying variation in beta diversity. We speculate that the large number of dams built upstream from the study area may account for the positive trend in beta diversity.