High seed dispersal rates in faunally intact tropical rain forest: theoretical and conservation implications

Dispersal limitation may promote high tree-species diversity in rain forest by slowing local competitive exclusion, but evidence is scarce. By comparing the species lists of tree plots with those of nested seedling plots in rain forest at Gunung Palung, we found that the proportion of local seedlings arising from active dispersal events (via wind or animals, but not simply dropped from parent trees) was high: 68% of species and 46% of the individual seedlings. Local seedling species richness was not limited by the local richness of adults. Using these data, a spatially explicit simulation model indicated that dispersal limitation may not contribute substantially to the maintenance of tree diversity in this forest. We predict that the loss of animal seed dispersers would reduce local species richness of seedlings by 60%. While this reduction could possibly increase the influence of dispersal limitation, it would interfere with other mechanisms maintaining diversity.