Faster diversification on land than sea helps explain global biodiversity patterns among habitats and animal phyla

Abstract

Terrestrial environments occupy ~ 30% of the Earth's surface yet contain ~ 80% of all species. The causes of this dramatic biodiversity gradient have remained relatively unstudied. Here, I test the fundamental prediction that predominantly non-marine clades have more rapid rates of diversification than marine clades, using a time-calibrated phylogeny of animal phyla. The results strongly support this hypothesis. This pattern helps explain the higher richness of terrestrial environments and the dramatic variation in species richness among animal phyla. The results show the importance of ecology in explaining large-scale patterns of clade richness and of diversification rates in explaining Earth's largest biodiversity patterns. The results also demonstrate remarkable niche conservatism in habitats, in some cases lasting > 800 million years. Finally, the results highlight the surprisingly high species richness of freshwater habitats, which are nearly equal to marine environments despite their much smaller area (~ 2% of Earth's surface vs. 70% for marine habitats).

Keywords: Animal phyla, diversification; freshwater; marine; niche conservatism; phylogeny, species richness; terrestrial.