Species packing and the latitudinal gradient in local beta-diversity

The decline in species richness at higher latitudes is among the most fundamental patterns in ecology. Whether changes in species composition across space (beta-diversity) contribute to this gradient of overall local species richness (gamma diversity) remains hotly debated. Previous studies that failed to resolve the issue suffered from a well-known tendency for small samples in areas with high gamma-diversity to have inflated measures of beta-diversity. We provide here a novel analytical test, using beta-diversity metrics that correct the gamma-diversity and sampling bias, to compare beta-diversity and species-packing across a latitudinal gradient in tree species richness of 21 large forest plots along a wide environmental gradient in East Asia. We demonstrate that after accounting for topography and correcting the gamma-diversity bias, tropical forests still have higher beta-diversity than temperate analogs. This suggests that local beta-diversity contributes to the latitudinal specie...