A new paper in PLoS Biology takes a combined spatial - evolutionary perspective on how more productive locations come to harbor a greater number of species. The study is by Alex Pigot, Joe Tobias and Walter Jetz, check it out here.
Summary: The increase in the number of species with the availability of energy in the environment is one of the most general but least understood patterns in global biodiversity. The finite amount of energy flowing through an ecosystem has long been suspected to place a fundamental constraint on the ability of species to subdivide ecological resources, with greater energy availability—and, thus, ecosystem productivity—in the tropics, potentially facilitating increased levels of coexistence. However, empirical support for this hypothesis has been lacking, raising the possibility that richness is higher in productive ecosystems for largely historical reasons, including the greater geological age and area of tropical biomes, which increases the period of time available for diversity to accumulate. By combining phylogenetic and geographic data from across the world’s bird species, we show that greater ecosystem productivity is associated with an increased probability of coexistence among closely related lineages and that this pattern contributes to the higher species richness in the tropics. Our results confirm that contemporary gradients in species richness are fundamentally shaped by energetic constraints on coexistence.