Species-area curves, spatial aggregation, and habitat specialization in tropical forests

The relationship between species diversity and sampled area is fundamental to ecology. Traditionally, theories of the species-area relationship have b een dominated by random-placement models. Such models were used to formulat e the canonical theory of species-area curves and species abundances. In th is paper, however, armed with a detailed data set from a moist tropical for est, we investigate the validity of random placement and suggest improved m odels based upon spatial aggregation. By accounting for intraspecific, smal l-scale aggregation, we develop a cluster model which reproduces empirical species-area curves with high fidelity. We find that inter-specific aggrega tion patterns, on the other hand, do not affect the species-area curves sig nificantly. We demonstrate that the tendency for a tree species to aggregat e, as well as its average clump size, is not significantly correlated with the species' abundance. In addition, we investigate hierarchical clumping a nd the extent to which aggregation is driven by topography. We conclude tha t small-scale phenomena such as dispersal and gap recruitment determine ind ividual tree placement more than adaptation to larger-scale topography. (C) 2000 Academic Press.