Fig. 1.

Present-day taxonomic and functional diversity patterns for marine bivalves along the continental shelf (water depths <200 m). Details of the recent marine bivalve dataset are provided in Recent Marine Bivalve Dataset. (A) Taxonomic richness of marine bivalve genera binned into 111-km² equal-area grid cells (∼1° of latitude at the equator). Global genus richness peaks in the Indo-West Pacific and is the location of the strongest latitudinal gradient across north–south coastlines. (B) Integrated occurrences of distinct genera across ° latitudinal bands reveal a broad richness peak within the tropics; species show a steeper gradient peaking at ∼10° N. (C) Functional richness, the number of distinct FGs, of marine bivalves per equal-area grid cell (binned as in A) peaks in the Indo-West Pacific, similar to genus richness in A. (D) Integrated occurrences of FGs across ° latitudinal bands show a global increase in FR from the tropics to the poles, with a fully saturated richness spanning nearly the entire tropics and warm-temperate zones. (E) Functional evenness of bivalve genera per equal-area grid cell measured as the inverse Simpson index and normalized by the number of FGs per cell (Materials and Methods; binned as in A). The lowest evenness occurs in the Indo-West Pacific, the region of highest taxonomic and functional diversity. While tropical regions of other coastlines are less even than the Indo-West Pacific, each coastline exhibits an increase in FE from the tropics to the poles. (F) FE increases globally from the tropics to the poles across ° latitudinal bands at both the genus and species levels.