The proportion of low abundance species is a key predictor of plant β‐diversity across the latitudinal gradient

Abstract The diversity of life displays very strong patterns of disparity across the Earth. Beta (β)‐diversity (species compositional differences among sites) of woody plants, for instance, has usually been documented to decline with increasing latitude. Understanding these patterns, however, remains a grand challenge in ecology and evolution. We develop a mathematical model to explain patterns of β‐diversity across multiple landscapes. The model effectively predicts β‐diversity in simulated and natural communities, regardless of the types of species abundance distributions. Our model provides the novel insight that the proportion of species in the lowest abundance category ( P L ), which represents the share of relatively rare species in the regional species pool, is the key predictor of plant β‐diversity. By applying the model to global forest inventories sampled from 40.7° S to 60.7° N, we find that P L explains nearly 85% of the variation in plant β‐diversity along the global latitudinal gradient. Through a series of numerical simulations, we further show that the predictive power of P L on plant β‐diversity on a global scale is largely determined by the variation of intraspecific aggregation among different communities. Synthesis : We develop a new sampling model to predict patterns of β‐diversity and find that the P L explains the majority of the variation in plant β‐diversity along the latitudinal gradient. Our work provides a new tool in analysing β‐diversity and advances the theoretical understanding of large‐scale β‐diversity patterns across environmental gradients.