PARENT SESSION
Oral Session # 10: Predator-Prey Ecology I: Terrestrial I: Theory and Cues.
Presiding: A Liebold
Monday, August 4. 8:00 AM to 11:30 AM, SITCC Meeting Room 202.

Mechanisms underlying variation in the impact of a keystone predator: Effects of an ant-homopteran mutualism on the numerical response and per-capita effects of ants.

Kaplan, Ian^*,1, Eubanks, Micky¹, ¹ Auburn University, Auburn, AL

ABSTRACT- Dominant species, such as keystone predators, can exert tremendous influence on the distribution and abundance of other organisms. However, the behavior and ensuing impact of these keystone species can be strongly affected by the presence of key interactors, such as mutualists. Our previous research documented that red imported fire ants, a keystone predator in many ecosystems of the Southern U.S., have a greater impact on arthropod food webs in the presence of honeydew-producing homopterans. These ants are attracted to honeydew, a sugary solution which homopterans excrete, and thus shift microhabitats from primarily soil-dwelling insects to foraging on plant foliage. It is still unclear, however, why ants have stronger community-wide effects when co-occurring with homopterans. The results of this study indicated that fire ants exhibit a strong numerical response to aphids; cotton plants with aphids attracted 11X as many ants as plants without aphids. Behavioral observations suggested that ants also behave more aggressively in the presence of aphids. Fire ants were more likely to attack and kill caterpillars while tending aphids than on aphid-free plants. These experiments imply that both enhanced ant recruitment (i.e., numerical response to aphids) and increased ant aggression (i.e., variation in the per-capita effect of individual ants) contribute to the keystone impact of fire ants on insect communities associated with cotton plants.

Key words: keystone predation, red imported fire ant, ant-homopteran mutualism, food web interactions