Differences in Aggressive Behaviors between Two Ant Species Determine the Ecological Consequences of a Facultative Food-for-Protection Mutualism

Abstract

Ant-hemipteran mutualisms are widespread interactions in terrestrial food webs with far-reaching consequences for arthropod communities. Several hypotheses address the behavioral mechanisms driving the impacts of this mutualism, but relatively few studies have considered multiple ant species simultaneously as well as interspecific and intraspecific variation in ant behavior. In a series of field experiments that manipulated ant diet, this work examines the role of induced behaviors of forest ant species actively engaged in mutualism with Hemiptera. Based on other work in ant mutualisms, we predicted a higher frequency of aggressive behaviors towards prey and competitors by ants in the presence of honeydew-producing Hemiptera. We specifically compared Camponotus chromaoides and Formica neogagates (Formicidae), two abundant species in temperate forests of the northeastern U.S.A. After manipulating ant diet and interactions with sap-feeders experimentally, we observed 494 one-on-one interactions between ants and competitors, ladybird beetles and caterpillar prey. We found that C. chromaoides, exhibited behavioral dominance over F. neogagates, and C. chromaoides was more likely to attack ladybird beetles, competing ants, and caterpillar prey. However, contrary to other work in ant-Hemipteran mutualisms, we observed no evidence that food rewards provided by sap-feeders induced changes in ant behavior for either ant species examined. These results reveal the importance of considering interspecific differences in behavior as a mechanism underlying the ecological impacts of ant-Hemipteran protection mutualisms.