Mammalian Insectivores Exert Top-Down Effects on Azteca Ants

Abstract

Insectivorous mammals are hypothesized to reduce the abundance of their insect prey. Using a 14-yr mammal exclusion experiment, we demonstrate for the first time that a widespread and abundant Neotropical mammalian insectivore (Tamandua: Tamandua mexicana) reduced Azteca ant abundance. Azteca ant nests inside mammal exclosures were significantly larger than nests in control plots, where tamanduas were more abundant. These top-down effects were caused not only by direct consumption, but also through non-trophic direct effects, specifically nest damage. In contrast, tamanduas appeared to exert no significant top-down effect on termite prey, which have strong chemical defenses. Our results are consistent with theory that strong defenses against predation can mitigate the top-down effects of predators on some prey species. We argue that predicting the degree of top-down effects caused by predators requires both a quantitative knowledge of prey choice and an understanding of the anti-predator defenses of prey.