For most marine organisms, species richness peaks in the Central Indo-Pacific region and declines longitudinally, a striking pattern that remains poorly understood. Here, we used phylogenetic approaches to address the causes of richness patterns among global marine regions, comparing the relative importance of colonization time, number of colonization events, and diversification rates (speciation minus extinction). We estimated regional richness using distributional data for almost all percomorph fishes (17,435 species total, including ~72% of all marine fishes and ~33% of all freshwater fishes). The high diversity of the Central Indo-Pacific was explained by its colonization by many lineages 5.3–34 million years ago. These relatively old colonizations allowed more time for richness to build up through in-situ diversification compared to other warm-marine regions. Surprisingly, diversification rates were decoupled from marine richness patterns, with clades in low-richness cold-marine habitats having the highest rates. Unlike marine richness, freshwater diversity was largely derived from a few ancient colonizations, coupled with high diversification rates. Our results are congruent with the geological history of the marine tropics, and thus may apply to many other organisms. Beyond marine biogeography, we add to the growing number of cases where colonization and time-for-speciation explain large-scale richness patterns instead of diversification rates.

Data and scripts from Miller et al.: Explaining the ocean’s dominant species richness gradient and global patterns of fish diversityData and R scripts from: Explaining the ocean’s dominant species richness gradient and global patterns of fish diversity Authors: Elizabeth Christina Miller, Kenji T. Hayashi, Dongyuan Song, and John J. Wiens Corresponding author: EC Miller (ecmiller 'at' email.arizona.edu or lizmiller2633@gmail.com) Please contact with questions or requests for additional material. R scripts are ordered following the Material and Methods section. Input files are included.Miller et al. Dryad September 11 2018.zip