COS 70-4 - Foraging strategy, community structure, and symmetry breaking in desert ants

Wednesday, August 10, 2011: 2:30 PM
4, Austin Convention Center
Michele C. Lanan , Entomology, University of Arizona, Tucson, AZ
Anna Dornhaus , Department of Ecology & Evolutionary Biology, University of Arizona, Tucson, AZ
Ginny M. Fitzpatrick , Ecology and Evolutionary Biology, University of Arizona, Tucson, AZ
Judith L. Bronstein , Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, AZ
Background/Question/Methods

We investigated the ecological and evolutionary significance of symmetry breaking, an emergent property of collective behavior in ant colonies. Symmetry breaking occurs when colonies presented with identical food sources allocate foragers among them asymmetrically, due to initial stochastic variation and positive feedback in pheromone recruitment. However, it is unclear whether symmetry breaking is simply an unavoidable epiphenomenon of pheromone recruitment, or whether it serves an adaptive function and can vary among pheromone recruiting species. In this study, we sought to compare symmetry breaking across species with different foraging strategies in an ant community. We hypothesized that in a community structured by a clear dominance hierarchy and trade-off between numerical dominance and discovery ability, the most dominant species rely heavily on recruitment and would therefore exhibit the most asymmetrical foraging.

Results/Conclusions

In the community we studied, competitive dominance was strongly correlated with how asymmetrically colonies foraged, with the highest-ranking species exhibiting the most asymmetry. The least dominant species, in contrast, exhibited low or no symmetry breaking despite their use of pheromone recruitment. In a community structured by a trade-off between numerical dominance and discovery ability, symmetry breaking may enable dominant species to recruit large numbers of workers to resources. Species lower in the hierarchy may need to avoid symmetry breaking in order to rapidly explore their environment and discover new food sources. We conclude that symmetry breaking is not simply an epiphenomenon of recruitment, and the degree to which it occurred in our system was related to the foraging ecology of the species tested.

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