UC Berkeley

A central goal of ecology is to understand the mechanisms behind variation in the abundance of species. Food web theory predicts higher biomass for animals at lower trophic levels. However, some high trophic level species may reach great abundance via highly efficient foraging behaviors. We evaluated ecological and behavioral traits of the giant tropical ant Dinoponera australis related to these mechanisms. We determined its distribution and abundance, documented its foraging behavior, and measured its trophic position in a population at P.N. Iguazú, Argentina. We report that D. australis colonies are overdispersed, and the species reaches a wet biomass of more than 2.5 kg/ha at this site. Dinoponera australis foraging behavior is characterized by route fidelity of individual workers, with different individuals specializing on different areas around the nest. Finally, stable isotopic evidence and direct observation suggest these ants are among the top predators in this terrestrial invertebrate community. We interpret our findings in the context of how the behavior of an abundant top predator creates an exception to the usual trade-off between biomass and trophic level. Together these data provide insight into the biology of one of the world's largest ants and why they may be able to attain such high densities where they occur. © 2014 The Association for Tropical Biology and Conservation.