Plants and the animals that eat them make up 50% of the organisms on earth and the interactions among them have profound implications for the diversity and dynamics of natural forests. Plants have evolved an astounding array of chemical defenses to deter herbivores, and herbivores have countered with detoxification mechanisms. This reciprocal selection is believed to be responsible for the great species diversity of tropical forests. However, we know little of the mechanisms shaping the strength of selection for effective plant defenses. This study will examine differences in the defensive chemistry of a widespread Neotropical genus, Inga, by comparing sites in Panama and Ecuador. We predict that herbivore abundance, and hence the selection for plants to defend themselves will be greater in the more diverse and non-seasonal forest in Ecuador. At each site we will quantify herbivore pressure, diversity and abundance of Inga, investments in non-protein amino acids and flavonoids (the main classes of chemical defenses in Inga), toxicity of defenses to herbivores in laboratory trials, and rates of damage to leaves in nature. Despite the presumed importance of reciprocal selection by herbivores and plants on the evolution of chemical defenses, very few studies have addressed this in complex natural communities.
