Global patterns and determinants of multiple facets of freshwater fishes beta diversity

Global patterns of freshwater fish species diversity and their natural and
anthropogenic determinants are relatively well documented. Yet,
determinants of fish dissimilarity (beta diversity) across river basins
remain poorly understood. Here, we quantify taxonomic, functional, and
phylogenetic beta diversity of freshwater fish across global river basins
and identify the key environmental and historical drivers shaping these
patterns. We used a global database of freshwater fishes, a trait database
based on morphological descriptions and phylogenetic information
calculated by phylogenetic distances. We assessed multiple facets of fish
beta diversity and partitioned beta diversity into turnover and nestedness
components to assess their contributions. Spearman correlation analysis
was conducted to assess the relationships between them and their
components. We then applied a boosted regression tree (BRT) model to
assess their relationship with key environmental, spatial, and historical
variables. We reported strong links between three facets of beta
diversity, but species turnover contributed more strongly than nestedness
to overall beta diversity, while functional and phylogenetic beta
diversity exhibited contrasting patterns. We further found that
geographic, climatic, and historical factors all played significant roles
in shaping beta diversity, with river basin area emerging as the most
influential predictor. Although the global patterns of the three facets of
beta diversity are consistent, the contributions of turnover and
nestedness are different. Our results suggest that distinguishing between
turnover and nestedness dimensions of the taxonomic, functional, and
phylogenetic facets of biodiversity provides a comprehensive and
insightful understanding of the mechanisms underlying global freshwater
fish beta diversity.