Spatial scale and dispersal influence metacommunity dynamics of benthic invertebrates in a large river

Taxon-specific dispersal ability can affect community composition, but little is known about how it influences metacommunity dynamics, particularly for taxa with large ontogenetic changes in dispersal mode and ability. The spatial scale of a study also can affect perceived or sampled community composition, but our understanding of the artifacts resulting from the spatial extent sampled is limited, and artifacts are difficult to differentiate from real metacommunity processes. We assessed community composition of benthic macroinvertebrates at nested spatial scales in a large river and used differences in dispersal as immature aquatic life stages and winged terrestrial adults to explain patterns in community structure. Spatial distribution of patches alone (space), followed by synergistic effects of space and environmental factors, and then environmental factors alone were the best predictors of community structure. As predicted by metacommunity theory, the local environment was a better predictor than was space for distributions of taxa with actively dispersing larvae and strong-flying winged adults than for distributions of taxa with passively dispersing larvae and weak-flying adults, particularly with increasing spatial scale. These results indicate that as dispersal ability increases, the processes affecting metacommunity structure change. The importance of spatial structure decreases whereas the importance of environmental factors increases with dispersal ability for both aquatic life stages and winged adults. In addition, increasing spatial grain and extent increase the ability of spatial structure to predict community composition. These results in conjunction with results of similar studies on small streams or interconnected ponds indicate that the ability of spatial structure and environmental factors to predict metacommunity structure may increase with increasing community connectedness.