Spatial and environmental processes show temporal variation in the structuring of waterbird metacommunities

Metacommunity theory provides a framework for assessing the role of spatial and environmental processes in structuring ecological communities and places emphasis on the role of dispersal. Four metacommunity perspectives have been proposed: species-sorting, patch dynamics, mass effects, and a neutral model. Metacommunity analysis decomposes the variance in communities into regional and local dynamics and ascribes it to one of these perspectives, although they are not always mutually exclusive. Although birds are a well-studied taxon, consensus around processes structuring freshwater avian metacommunities is lacking and few studies have repeated samples through time. We used variance partitioning to analyze waterbird community data collected over seven sampling periods at 60 wetland sites in KwaZulu-Natal, South Africa, to distinguish the processes driving beta-diversity and identify which metacommunity perspective(s) best explained these patterns. We addressed two focal questions: (1) how do environmental, spatial, and spatially structured environmental components contribute to variance in the waterbird community; and (2) given a significant contribution, which environmental variables were most important in explaining metacommunity structure? We also investigated the role of temporal variation in community processes by comparing results across sampling periods. The underlying landscape was characterized by four groups of environmental variables: vegetation structure, water quality, rainfall, and land cover. Moran's eigenvector maps were used to generate a set of multiscale spatial predictor variables. Our results showed that the spatially structured environmental component was dominant through the sampling periods. Purely spatial and environmental components contributed a significant proportion of variance, but their magnitudes showed considerable temporal variation. Environmental processes were more pronounced in winter periods while purely spatial processes were augmented in the summer months. Our results suggest that species-sorting is the primary structuring forces in waterbird communities. The presence of spatial effects, especially in summer, does however suggest that species-sorting does not operate in isolation. Future efforts also need to address the causes and consequences of temporal variation in metacommunity processes