Metacommunity structure of zooplankton in river networks: Roles of environmental and spatial factors

Abstract

Zooplankton in river systems have seldom been studied in the context of metacommunity ecology. Spatial factors (e.g., river connectivity, directionality, and man-made dams) may play a key role in influencing the metacommunity structure of rotifers because of their small body size and weak mobility. In contrast, local environmental factors (e.g., physicochemical habitat) may be more important to crustaceans due to their larger body size and stronger mobility. We sampled zooplankton and environmental factors during wet and dry seasons from 47 sites along the Ying River in China to assess the roles of the spatial and environmental factors in structuring zooplankton metacommunities. We used Moran’s eigenvector map and asymmetric eigenvector map to model the influences of river connectivity, directionality, and man-made dams on zooplankton metacommunity structure. We then used partial redundancy analysis to identify individual and interactive effects of spatial and environmental factors on both the entire zooplankton assemblages and two zooplankton groups of different body sizes and mobility. A total of 101 taxa were identified and taxa richness was higher in the wet season (72) than in the dry season (58). Zooplankton assemblages were primarily dominated by rotifers. For the dry season, environmental factors such as total nitrogen, water temperature, and pH explained a significant portion of variation in zooplankton community; river connectivity was more important than river directionality to zooplankton metacommunity structure. For the wet season, spatial factors were more influential than environmental factors such as dissolved oxygen and water transparency; river directionality played an important role in influencing the spatial structures of both environmental condition and zooplankton metacommunity. We also found significant effects of man-made dams on zooplankton metacommunity structure. Spatial factors are more influential in structuring small body size and weak mobility rotifer communities, while environmental factors are more important in determining the variation of crustaceans due to their larger body size and stronger mobility. We concluded that river connectivity and directionality should be considered as key factors for better understanding the spatial processes of planktonic passive dispersers in river networks. Our study provides new insight on understanding riverine zooplankton metacommunity ecology and contributes to the knowledge of river ecosystem health monitoring and management.