A spatially explicit neutral model of b-diversity in tropical forests

To represent species turnover in tropical rain forest, we use a neutral model where a tree’s fate is not affected by what species it belongs to, seeds disperse a limited distance from their parents, and speciation is in equilibrium with random extinction. We calculate the similarity function, the probability F (r) that two trees separated by a distance r belong to the same species, assuming that the dispersal kernel P (r), the distribution of seeds about their parents and the prospects of mortality and reproduction, are the same for all trees regardless of their species. If P (r) is radially symmetric Gaussian with mean-square dispersal distance r; F ðrÞ can be expressed in closed form. If P (r) is a radially symmetric Cauchy distribution, then, in two-dimensional space, F (r) is proportional to 1=r for large r: Analytical results are compared with individual-based simulations, and the relevance to field observations is discussed. & 2002 Elsevier Science (USA) Key Words: data diversity; long-distance dispersal; neutral model; tropical forest 1