Insect Herbivory in Tropical Forests

In z.n address to inaugurate the invertebrate exhibit at the National Zoo, Washington, DC on Mav 7, 1987, E.O. Wilson called insects "the little things that run the world" (Wilson 1987a). In terris of their diversity, distribution, and abundance, insects are unrivaled as a global ecolo,gical and evolutionary force. "It needs to be repeatedly stressed that invertebrates as a whole are even more important in the maintenance of ecosystems than are vertebrates" (Wilson 1987a). In a single tree in the Peruvian Amazon, Wilson found -13 species of ants (Wilson 1987b). Erwin (1982) discovered more than 1,000 kinds of beetles on 19 individual trees of a single species, Luehea seemannii, in a seasonal lowland forest in Panama. From this discovery, Erwin extrapolated an estimate of 30 million species of organisms on the planet (Erwin 1982, 1983j.l In terms of biomass, insects in tropical forests constitute several tons per hectare conlpared to a few kilograms per hectare for birds and mammals (reviewed in Dajoz 2000). Eight million ants and one million termites per hectare make up more than one-third the animal biomass in Amazonian t e r ra jma rainforest (Holldobler and Wilson 1990). If we limit this discussion only to their bulk in the treetops, these humble hymenopterans and associates still represent a significant portion of the total animal biomass for tropical forests. For nearly a quarter-century, we have known that canopy arthropods are key regulators of ecosystem processes (Reynolds et al. 2000). Insects then are the little things that run our forests-indeed most terrestrial ecosystems-from top to bottom.