Do Mammals and Insects Control Tropical Forest Diversity? A Community-level Experimental Test

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This proposal challenges the prevalent view about tropical forests that gap phase dynamics is the most important part of the regeneration cycle for determining species composition of tropical forests. This research is the first to experimentally test the hypothesis that mammals and insects in the understory of mature tropical forest control tree species diversity. This hypothesis has important ramifications for tropical forest dynamics, diversity, conservation, and management. Recent observations suggest that when forests lose their mammalian herbivores and seed predators they develop low plant species diversity. Forests with intact mammalian fauna have high species diversity. Poaching and over-hunting in many tropical forest reserves are threatening mammalian herbivore populations. If mammalian herbivores are important, than forests that lose their fauna are likely to lose tree species diversity at an accelerated rate. The forest on Barro Colorado Island (BCI), Panama, will be studied in this research. Our findings indicate that gaps do not affect species diversity in these forests; therefore, the abundance of tree species must be determined in the understory where seeds, seedlings, and saplings are exposed to intensive herbivory. We propose to test the hypothesis that herbivory and seed dispersal control the establishment, composition, and diversity of tree species in species-rich tropical forests. %%% For the past ten years, research in tropical forests has focused on the role of gap-phase dynamics as the primary determinant of tree species diversity. Although studies of seed predation are common, this project represents the first attempt to conduct a community-level experimental test of the effects of mammalian and insect herbivores on tropical forest diversity. The results have important implications for the conservation and management of biodiversity in tropical regions.