9318543 Letourneau Understanding the forces that structure biotic communities is of fundamental importance in ecology, conservation, biology, and biological control (agriculture). Yet there is currently no consensus about whether predators usually control community structure (top-down control), or whether plant productivity usually controls community structure (bottom-up control). This research will use an experimental system of one plant species (Piper cenocladum), several insect herbivore species, one predatory ant species, and two ant predator species, to test these alternatives for the first time in a tropical terrestrial ecosystem. The project uses common-garden experiments to assess the effects of the fourth trophic level (ant predators) on the dynamics of secondary and primary consumers, and producers (top-down), and to quantify the effects of nutrient and light enhancement on the plants and on higher trophic levels (bottom-up). %%% Results from this research will provide important insights into the relative strengths of top-down and bottom-up controls in tropical terrestrial ecosystems. The results will advance our understanding of how terrestrial ecosystems are structured and how ants, plants, and herbivores interact. The results of this research will also have potential applications in conservation biology and in the development of biological control systems for agriculture and forestry. ***