PARENT SESSION
Oral Session 67: Mutualism - Parasitism III: Ants.
Presiding: K Mooney
Wednesday, August 4, 8:00 AM to 11:30 AM, Meeting Room D 135.

Attack by phorid flies enforces the dominance-discovery trade-off in an assemblage of woodland ants.

LeBrun, Edward^*,1, Feener, Donald², ¹ University of California San Diego, La Jolla, CA² University of Utah, Sale Lake City, UT

ABSTRACT- Trade-offs between interference and exploitative competitive ability provide a mechanism for explaining species coexistence within guilds that exploit highly overlapping resources. Omnivorous, leaf litter ants exploit a shared food base and occur in species rich assemblages. In these assemblages, species that excel at usurping food items from other species are poor at finding food items first. The balance of terror model derives this assemblage-level trade-off curve from the interacting forces of resource competition and attack by specialist parasitoids. This study tests the predictions of the balance of terror model in an assemblage of ants where phorid fly parasitoids attack two of the behaviorally dominant members as they attempt to harvest food resources. The major findings are that unparasitized species in the assemblage follow a dominance-discovery trade-off curve. When not subject to attack by phorid flies, host species violate that trade-off by finding resources too quickly for their level of behavioral dominance. In contrast, when attacked by their phorid parasitoids, the host species dominance drops such that they fall into the assemblage trade-off. The behavior of the host species matches the predictions of the balance of terror model for an inducible defense. However, the balance of terror does not provide an explanation for the dominance-discovery trade-off among the unparasitized species.

Key words: interference-expoitation trade-off, Phoridae, community ecology, ants