Dispersal costs affect taxonomic and functional beta diversity of riverine fish assemblages

Abstract The dispersal of fish along river segments is dependent on resistance factors such as channel slope, dam attributes, and the watercourse distance between locations. We examined how such dispersal costs shape the taxonomic and functional beta diversity of fishes in four basins in the Eastern United States of America. We clustered the fish species into functional groups defined using swimming and reproductive traits. We found that dispersal costs explained a greater percentage of functional beta diversity based on swimming traits than using reproductive traits, although large variation was evident across basins. Watercourse distance explained the highest percentages of beta diversity compared to other costs. However, we still found evidence for the effect of dams, particularly when using dam height and dam age as explanatory attributes. The functional group of small body sizes was more associated with dispersal costs than other functional groups based on swimming traits. Within the functional reproductive groups, intermediate and equilibrium species were more associated with dispersal cost variables. Our study indicates that dispersal costs affect within-basin fish dispersal and influence the distribution of functional groups, although basin contingencies greatly affect our ability to understand species and trait composition of fish assemblages.