Spatial pattern analysis of tree species distribution in a tropical rain forest of Cameroon: assessing the role of limited dispersal and niche differentiation

Tree species distribution has been investigated along 45 km of line transects in the tropical rain forest of the Dja Fauna Reserve in Cameroon. The spatial patterns were expressed by the probabilities that two trees are conspecific according to the distance separating them, providing information on the degree of species clumping as well as on alpha- and beta-diversity. Our objective was to assess the relative importance of habitat heterogeneity and limited dispersal in determining these patterns by: (1) comparing the patterns observed within and across major habitats; (2) comparing the patterns with the ones expected under a neutral hypothesis where limited dispersal is the sole factor. Although, habitat heterogeneity affected the distribution of many species, our results suggest that limited dispersal was the major factor affecting the degree of species clumping. The pattern observed was similar to the one found in Amazonia by Condit et al. [Science 295 (2002) 666]. We discuss the relevance of neutral models of tree communities to study the dispersal abilities of tree species.