Area and the latitudinal diversity gradient for terrestrial birds

We tested the hypothesis that area represents the primary explanation for t he latitudinal diversity gradient using breeding terrestrial birds of North America, the northern Palearctic, Australia and the Afrotropics as our foc al group. We tested two propositions inherent to the area hypothesis: (1) t ropical biomes are larger than extra-tropical biomes, and (2) there is a si gnificant species-area relationship for birds at the biome scale of resolut ion. Using a more realistic definition of biomes which incorporates the eff ects of both energy and water, we find no support for either proposition, l eading us to conclude that the area per se does not explain terrestrial lat itudinal diversity gradients.