Integrating abundance and functional traits reveals new global hotspots of fish diversity

Species richness has dominated our view of global biodiversity patterns for centuries1,2. The dominance of this paradigm is reflected in the focus by ecologists and conservation managers on richness and associated occurrence-based measures for understanding drivers of broad-scale diversity patterns and as a biological basis for management3,4. However, this is changing rapidly, as it is now recognized that not only the number of species but the species present, their phenotypes and the number of individuals of each species are critical in determining the nature and strength of the relationships between species diversity and a range of ecological functions (such as biomass production and nutrient cycling)5. Integrating these measures should provide a more relevant representation of global biodiversity patterns in terms of ecological functions than that provided by simple species counts. Here we provide comparisons of a traditional global biodiversity distribution measure based on richness with metrics that incorporate species abundances and functional traits. We use data from standardized quantitative surveys of 2,473 marine reef fish species at 1,844 sites, spanning 133 degrees of latitude from all ocean basins, to identify new diversity hotspots in some temperate regions and the tropical eastern Pacific Ocean. These relate to high diversity of functional traits amongst individuals in the community (calculated using Rao’s Q6), and differ from previously reported patterns in functional diversity and richness for terrestrial animals, which emphasize species-rich tropical regions only7,8. There is a global trend for greater evenness in the number of individuals of each species, across the reef fish species observed at sites (‘community evenness’), at higher latitudes. This contributes to the distribution of functional diversity hotspots and contrasts with well-known latitudinal gradients in richness2,4. Our findings suggest that the contribution of species diversity to a range of ecosystem functions varies over large scales, and imply that in tropical regions, which have higher numbers of species, each species contributes proportionally less to community-level ecological processes on average than species in temperate regions. Metrics of ecological function usefully complement metrics of species diversity in conservation management, including when identifying planning priorities and when tracking changes to biodiversity values.

We thank the many Reef Life Survey (RLS) divers who participated in data collection and provide ongoing expertize and commitment to the program, University of Tasmania staff including T. Cooper, M. Davey, N. Barrett, J. Berkhout and E. Oh, and T. Bird for assistance running models and checking code. Development of the RLS data set was supported by the former Commonwealth Environment Research Facilities Program, and analyses were supported by the Australian Research Council, Institute for Marine and Antarctic Studies, and the Marine Biodiversity Hub, a collaborative partnership supported through the Australian Government’s National Environmental Research Program. Additional funding and support for field surveys was provided by grants from the National Geographic Society, Conservation International, Wildlife Conservation Society Indonesia, The Winston Churchill Memorial Trust, and ASSEMBLE Marine.