A system in which available energy per se controls alpha diversity: marine pelagic birds.

An attractive explanation for large-scale gradients of species richness is that trophic energy flux defines living systems. It has yet to be shown that available energy may matter per se, that is, directly and independent of other potential determinants that are usually inescapably correlated (e.g., area, glacial history, or habitat complexity). By using a comprehensive conceptual framework addressing the variation of species richness, we report that in communities of birds regularly foraging in marine pelagic waters during the breeding season, species richness is above all directly linked to the appropriation of metabolic energy. Auxiliary energy supplied by wind and waves is likely to mitigate energetic constraints and thereby codetermine the expansion of niche space, along with an array of other subordinate factors. We emphasize that this system is markedly different from studied communities of terrestrial endotherms or marine exotherms in which habitat complexity and mutagenic solar radiation/temperature, respectively, may be more decisive than the appropriation of trophic energy flux shares as such. While the seabird system suggests that species-energy curves may sometimes directly translate into species-energy relationships, this situation may be rare rather than typical.