Species abundances surpass richness effects in the biodiversity-ecosystem function relationship across marine fishes

High biological diversity (or biodiversity) is thought to bolster communities against disturbances, leading to higher levels of ecosystem functioning. While the biodiversity-ecosystem function (BEF) relationship is evident in studies equating diversity to species richness, it is still unclear which ecological mechanisms can produce different observational BEF effects. Here, we combine 7686 individual growth curves across 1480 species with 2957 local community surveys to generate a process-based estimate of biomass production to assess the BEF relationship across marine reef fishes. We find that the effects of Hill diversity emphasising abundances outpace those of species richness and community evenness on biomass productivity. In high-latitude temperate regions, species abundances and richness have parallel effects on reef fish productivity. However, in the tropics, species abundances surpass species richness in their effects on functioning. These latitudinal disparities can be explained by trade-offs in the relationship between abundance and per-capita productivity. As whole-community productivity remains relatively stable across most of the diversity gradient, these trade-offs are presumably driven by metabolic constraints on growth and body size imposed by warmer temperatures. It appears that biodiversity can only support ecosystem functioning to a limited extent and environmental stressors likely limit the biomass production of marine fishes globally.