Linked indirect effects in ant-phorid interactions: impacts on ant assemblage structure

Interaction modifications arise when the presence of one species alters the behavior of a second thereby altering that species' interactions with a third. Species-specific phorid parasitoids that attack ants at food resources can modify the competitive interactions between their host and competing ant species. This study examines whether interaction modifications created during interactions between the phorid fly parasitoid, Apocephalus sp. 8, its host, Pheidole diversipilosa, and ant species with which P. diversipilosa competes determine P. diversipilosa's foraging success. We also explore how varying resource size affects the ability of P. diversipilosa to capture resources and if this factor changes the nature or magnitude of the interaction modifications. We find that conflict between the host ant and competitor species at resources greatly improves the ability of the parasitoid to locate its host. In addition, the presence of a parasitoid at a food resource strongly reduces the ability of the host ant to capture that food resource when competing with other ant species. A wide variety of competitor species benefit from these linked interaction modifications and do so in accordance with their abundance in the assemblage. Finally, the size of the food resource in dispute affects the ability of the host ant to capture the resource, but parasitism and resource size affect resource turnover independently. These results are relevant to understanding the importance of interaction modifications in determining structure of ant assemblages.