Urbanization increases biotic homogenization of zooplankton communities in tropical reservoirs

Under rapid urbanization, many reservoirs built in rural areas are being embraced into by nearby expanding cities. Anthropogenic activities in urban areas can strongly affect aquatic biodiversity by modifying aquatic landscape and reduce habitat heterogeneity. As one of the key components in reservoir ecosystems, zooplankton is sensitive to such habitat changes. Within the metacommunity framework, we predict that in an urbanized landscape: (1) species sorting becomes the most important process in determining the variation of zooplankton communities; (2) urbanization will result in low beta-diversity and biotic homogenization of zooplankton communities and such homogenization will not significantly vary across time. To test these predictions, we investigated twenty five permanent reservoirs over three hydrological seasons in a well-developed and rapidly expanding city in tropical China. The reservoirs were grouped into two location classes and three storage size classes. Our results suggested that the structure of zooplankton communities were strongly homogenized in the studied urban reservoirs as being reflected in the low beta-diversity between the two location classes. However, high beta-diversity was found within each storage size class, mainly derived from species turnover (beta(sim)). The high beta-diversity indicated that the variation of zooplankton community is a consequence of environmental heterogeneity within each storage size class. Variation partitioning revealed a weak spatial structure for zooplankton communities at the large scale, while only Chla as an indicator of food supply significantly explained high community variation among reservoirs in the dry season, but not in wet and transition seasons despite apparent species seasonal succession.