Resources and global avian assemblage structure in forests

Explaining spatial variation in a number of bird species, particularly from temperate to tropical regions, has been a longstanding challenge. We test at a global scale whether species-rich forest assemblages are associated with division of a larger resource pool, a finer division of that pool, or some combination of the two. Species richness increases with increasing assemblage abundance, biomass and energy use. As assemblage abundance, biomass and energy use increase with increasing energy availability, and as per species numbers of individuals, biomass and energy use do not decrease with increasing energy availability, we provide direct evidence that the avian species-energy relationship in forests is associated foremost with an increase in the size of the resource pool and not with a finer level of its subdivision.