Sarah E. Wittman1, Nicholas J. Gotelli1, Nathan J. Sanders2, and Aaron E. Ellison3. (1) Biology, University of Vermont, Burlington, VT 05405, (2) Ecology and Evolutionary Biology, University of Tennessee, Knoxville, TN 37996, (3) Harvard Forest, Harvard University, Petersham, MA 01366
Many studies suggest competitive interactions strongly structure ant communities, although few studies have experimentally examined its role. We evaluated competitive structuring of ant communities of the Siskiyou-Klamath Ecoregion with null models, Markov models derived from behavioral interaction data, and experimental removals of putative competitors. Ant species foraging on a 64m2 grid of 50 tuna and honey baits were sampled 9 times throughout the day at 16 sites in during the summer of 2003 and 2004. We used a null model to determine if species co-occur randomly or non-randomly at different times of the day. We established pairwise behavioral arena contests between the seven most common species to determine the probability of persistence (proportion non-retreats) vs. expulsion (proportion retreats) of each species pair encounter. We used these data to construct a Markov model to predict the relative abundance of each species, assuming agonistic behavior determines foraging abundance. Finally, we removed an aggressive species (Formica moki) from half of our bait stations throughout the 2005 summer. In the null model analyses, we found that species co-occur less often than chance in three sites (19%) in the morning, zero sites in the afternoon, and five (31%) sites in the evening. Markov models based on pairwise species interactions did not accurately predict relative abundance at the local scale. Finally, species removal had a significant effect on the foraging behavior of Temnothorax nevadensis, whereas recruitment and bait monopolization by other species were unaffected. Our results suggests that other factors, such as temperature and microhabitat heterogeneity, may play a larger role than competitive interactions in structuring Siskiyou-Klamath ant communities.
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