PARENT SESSION
Oral Session #6: Insect Population and Community Ecology: Interactions, foodwebs.
Presiding: M. Hunter
Monday, August 5. 8:00 AM to 11:30 AM. Apache Meeting Room, TCC.

Keystone mutualisms and the ecological consequences of manipulation: cascading effects of an ant-aphid interaction.

KAPLAN, IAN^*,1, EUBANKS, MICKY¹, ¹ Auburn University, Auburn, AL

ABSTRACT- Keystone predators are defined by their high trophic status and ability to alter the distribution and abundance of multiple species in complex food webs. We believe that red imported fire ants, Solenopsis invicta (Buren) (Hymenoptera: Formicidae), act accordingly and function as keystone predators. We have studied the impact of fire ants on the arthropod communities of southeastern agroecosystems and have documented pervasive effects of fire ants on arthropod predators and herbivores. Surprisingly, however, the density of fire ants did not accurately predict their impact on other arthropods. In this study, we investigated the role of a fire ant-cotton aphid mutualism on the community-wide effects of fire ants. We found that fire ants actively tend cotton aphids, Aphis gossypii. Fire ants collect and consume the sugar-rich honeydew produced by the aphids. In exchange for honeydew, we found that fire ants protect aphids from natural enemies such as lady beetles and green lacewings. Similarly, fire ants release aphids from competition. Fire ants were significantly more likely to attack herbivores on aphid-infested plants than on aphid-free plants. We also found that the effect of fire ants on other arthropods was positively correlated with aphid density in both greenhouse and field experiments. Consequently, the effect of fire ants as keystone predators may be a direct function of the density of a keystone mutualist.

KEY WORDS: red imported fire ant, cotton aphid, keystone predation, mutualism