Taxonomic and phylogenetic β-diversity of freshwater fish assemblages in relationship to geographical and climatic determinants in North America

Aim: A full understanding of the origin and maintenance of beta-diversity patterns in a region requires understanding of: (1) the relationships of both taxonomic and phylogenetic beta-diversity (TBD and PBD, respectively) and their respective turnover and nestedness components with geographical and environmental distances; (2) the relative importance of the turnover and nestedness components of beta-diversity; and (3) the relationships between PBD measures representing different evolutionary depths. Here, we investigate all these aspects of beta-diversity simultaneously for freshwater fishes in North America. Location: North America north of Mexico (hereafter, North America). Taxon: Freshwater fishes. Methods: North America was divided into 360 watersheds. Using two sampling approaches (neighbourhood vs. pairwise), we quantified beta-diversity between fish assemblages using various metrics (representing total, turnover and nestedness components of TBD and PBD, and tip- vs. basal-weighted PBD) and related them to geographical and climatic factors using correlation and regression analyses. Results: Geographical patterns of total TBD and PBD and their components of turnover and nestedness for freshwater fish assemblages among neighbouring watersheds were highly congruent across North America. Geographical patterns of basal-weighted PBD were generally opposite to those of tip-weighted PBD. Metrics of beta-diversity were weakly associated with contemporary climatic variables. TBD and PBD were associated strongly to moderately with geographical distances and moderately with climatic distances. The relationships of metrics of beta-diversity to geographical distances were stronger than those to climatic distances in all cases. Main conclusions: Geographical and ecological patterns are highly congruent between taxonomic and tip-weighted PBD, but those between tip- and basal-weighted PBD are greatly different, suggesting that evolutionary histories have played an important role in shaping beta-diversity. Our study suggests that geographical distance between watersheds is more important than climate similarity in determining beta-diversity between freshwater fish assemblages.

Automated summary

This study examined various aspects of beta-diversity patterns in North American freshwater fishes, finding high congruence in geographical patterns of total TBD and PBD, turnover, and nestedness components among neighboring watersheds. The results also highlighted the opposite patterns of basal-weighted PBD compared to tip-weighted PBD, and the stronger influence of geographical distance over climate similarity in determining beta-diversity in freshwater fish assemblages.