Synthesis reveals approximately balanced biotic differentiation and homogenization

This work was supported by the German Research Foundation (FZT 118, to S.A.B., T.E., A.S., R.v.K., W.-B.X., and J.M.C.) and ERC GA 101044975 and the Leverhulme Centre for Anthropocene Biodiversity (to M.D.). This work was also supported by the German Research Foundation (DFG) project “Establishment of the National Research Data Infrastructure (NFDI)” in the consortium NFDI4Biodiversity (project number 442032008) (to T.E.), European Union Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement no. 894644 (to I.S.M.), USDA Hatch grant MAFES #1011538 and NSF EPSCOR Track II grant #2019470 (to B.M.), and NSF Track II grant #2019470 (to N.J.G.).It is commonly thought that the biodiversity crisis includes widespread declines in the spatial variation of species composition, called biotic homogenization. Using a typology relating homogenization and differentiation to local and regional diversity changes, we synthesize patterns across 461 metacommunities surveyed for 10 to 91 years, and 64 species checklists (13 to 500+ years). Across all datasets, we found that no change was the most common outcome, but with many instances of homogenization and differentiation. A weak homogenizing trend of a 0.3% increase in species shared among communities/year on average was driven by increased numbers of widespread (high occupancy) species and strongly associated with checklist data that have longer durations and large spatial scales. At smaller spatial and temporal scales, we show that homogenization and differentiation can be driven by changes in the number and spatial distributions of both rare and common species. The multiscale perspective introduced here can help identify scale-dependent drivers underpinning biotic differentiation and homogenization.Peer reviewe

Coral settlement and recruitment are negatively related to reef fish trait diversity

The process of coral recruitment is crucial to the functioning of coral reef ecosystems and recovery of coral assemblages following disturbances. Fishes can be key mediators of this process by removing benthic competitors like algae, but their foraging impacts are capable of being facilitative or harmful to coral recruits depending on species traits. Reef fish assemblages are highly diverse in foraging strategies, and the relationship between this diversity with coral settlement and recruitment success remains poorly understood. Here, we investigate how foraging trait diversity of reef fish assemblages covaries with coral settlement and recruitment success across multiple sites at Lizard Island, Great Barrier Reef. Using a multi-model inference approach incorporating six metrics of fish assemblage foraging diversity (foraging rates, trait richness, trait evenness, trait divergence, herbivore abundance, and sessile invertivore abundance), we found that herbivore abundance was positively related to both coral settlement and recruitment success. However, the correlation with herbivore abundance was not as strong in comparison with foraging trait diversity metrics. Coral settlement and recruitment exhibited a negative relationship with foraging trait diversity, especially with trait divergence and richness in settlement. Our findings provide further evidence that fish play a role in making benthic habitats more conducive for coral settlement and recruitment. Because of their ability to shape the reef benthos, the variation of fish biodiversity is likely to contribute to spatially uneven patterns of coral recruitment and reef recovery