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

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 (PL), 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 PL 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 PL 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
proportion of species in the lowest abundance category explains the
majority of the variation in plant β-diversity along the latitudinal
gradient. Our work provides a new tool in analyzing β-diversity and
advances the theoretical understanding of large-scale β-diversity patterns
across environmental gradients.