Global patterns and drivers of beta diversity facets of reef fish faunas

Aim: Exploring the relationships between the different facets of beta diversity and both past and current environmental conditions can unveil the processes that have shaped spatial patterns of biodiversity. In the marine realm, large-scale patterns and processes of beta diversity have been less investigated. Our study aimed to investigate the patterns and drivers of multiple facets of beta diversity and its components, contrasting pairs of reef fish assemblages among marine realms. Location: Tropical reefs. Taxon: Reef fishes. Methods: Based on trait data and phylogenetic relationships for 5,182 tropical reef fish species, we calculated compositional differences between pairs of reef fish assemblages across the Atlantic, Tropical Eastern Pacific (TEP), and Indo-Pacific realms. We also applied a partitioning approach to distinguish between the turnover and nestedness components. We then evaluated the relative importance of several variables related to historical and contemporary environmental conditions in shaping spatial patterns of beta diversity using Constrained Analysis of Principal Coordinates (CAP) models. Results: Both the turnover and nestedness components contributed to total phylogenetic and taxonomic beta diversity in the TEP and Indo-Pacific realms, while the turnover component was found to be more important in the Atlantic realm. In contrast, total trait beta diversity displayed very low values and was primarily explained by the nestedness component. Taxonomic and phylogenetic differences in the composition of tropical reef fish assemblages were influenced by both historical and contemporary factors or solely by historical variables. Main conclusions: Our results suggest that past climate changes and historical contingency left an imprint in the present-day composition of tropical reef fish assemblages. The very low levels of trait beta diversity indicate that reef fish assemblages display similar trait composition even among geographically distant assemblages with contrasting evolutionary histories, which may result from environmental filtering or evolutionary convergence, or the combination of both processes