Quantifying and comparing the impacts of plant resources and consumers on ecological communities has been difficult for terrestrial ecologists, but it is an important component of understanding how natural and managed ecosystems are structured and how they respond to perturbations. The ant-plant, Piper cenocladum, and its associated arthropods have been a useful system for examining the effects of top-down and bottom-up manipulations in a tropical rain forest. The proposed experiments will directly compare the importance of plant secondary metabolites (amides) in regulating herbivory versus the role of ants. The experiments will also address specific questions about how these secondary metabolites mediate interactions between the four trophic levels. Field and shade house experiments will be conducted to test several hypotheses. Predators and resources will also be manipulated and changes in plant chemistry, plant biomass, herbivore numbers, and biomass of upper trophic levels will be examined. Herbivore feeding experiments will be conducted to further examine the effects of amides on herbivores. This research is an important step towards gaining an clear understanding of the trophic cascades observed in this model system. It will test the "green desert" model, which suggests that plant secondary compounds are important in shaping communities, because most plants are not usable resources for herbivores. It will also shed light on the roles of resource availability and plant chemistry in modifying trophic cascades. The larger questions addressed by this research are relevant to current theories about resource availability and chemical defense, controversies about the relative importance of factors that regulate herbivore populations, and advances in studies of ant-plant mutualisms. The results will allow an improved assessment of current theory and better inform practical decisions in the areas of conservation biology and biological control.
