Testing Multiple Mechanisms of Species Coexistence in a Guild of African Acacia-ants

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0089706. Maureen Stanton. Understanding the mechanisms, which facilitate the coexistence of species, is a focal area of contemporary ecology. The proposed project addresses such issues by examining the factors that allow four species of ants, which are obligately associated with swollen thorn acacias in Kenya, to co-exist on a single species of acacia, Acacia drepanolobium. A series of alternative hypotheses will be examined using observational, manipulative, and modeling approaches. The first hypothesis is that the likelihood of coexistence is enhanced to the extent that a trade off exists between colonization and competitive ability. Preliminary data suggest that the two competitively dominant species of ants are limited colonizers that principally extend into new areas via colony expansion, whereas colonization by the two competitively inferior species is accomplished by foundress queens. Proposed research will elucidate the differential role of colonization and local competition in determining coexistence. The second hypothesis is that coexistence is enhanced if subordinate ant species have an advantage conferred by temporal priority. Planned experiments will determine the benefit derived from persistence, which is associated with host tree modification by subordinate ant species. The third hypothesis is that coexistence is facilitated because competitively dominant species are at greater risk from natural enemies than are less abundant subordinate species. Preliminary data suggest that this is less likely because rates of parasitism and predation are generally low for all four species of ant. The fourth hypothesis is that differential exploitation of patchy resources in a heterogeneous environment increases the likelihood of coexistence. Preliminary data suggest that dominant species replace subordinant species in high quality patches, whereas subordinant species are more common in low quality patches. Planned experiments will assess whether the outcome of competitive interactions is dependent on patch quality. Results from these experiments will be integrated into a matrix projection model, which will assess the stability of ant communities and the role of spatio-temporal variation in long-term community dynamics.