An Analysis of Colony Movement and The Effects of Movement on Fitness in the Western Harvester Ant, Pogonomyrmex Occidentalis



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Colony movement in ants (Hymenoptera: Formicidae), is well documented and several studies have explored the fitness costs and causes of colony movement in different species. Attempts to describe the purpose or patterns of colony movement have been made on many species within Pogonomyrmex spp. However, research into these aspects of colony movement has yet to be described in P. occidentalis, The Western Harvester ant. This thesis examines the fitness costs, potential causes, and behavioral syndrome associated with colony movement in P. occidentalis. I analyzed Dr. Cole & Dr. Wiernasz's data from 1993-2023 on colony movement, age, size, distances traveled, and survivorship for 6,066 colonies. Moved colonies were found to have a smaller colony size, shorter colony lifespan, and lower rates of survivorship when compared to unmoved colonies using t-tests and a Kaplan-Meier survivorship analysis. Moreover, moved colonies were compared against 1-year-old colonies, and were found to have a larger colony size. Colonies were also found to have a greater tendency to move later in age, and 16.6% of colonies had moved at least once. These results suggest that colonies that move incur fitness costs, as colony size and lifespan are proxies for fitness, and that colony movement is more costly for younger or smaller colonies. Furthermore, because P. occidentalis is notably long-lived, shows high nest fidelity, and their movements are associated with a loss in fitness, they likely exhibit an adventitious nest relocation syndrome. Through this thesis, we can better contextualize P. occidentalis in the greater scheme of animal architects and the decisions they make.



Colony movement, Nest relocation, Animal architect, Western harvester ant, Fitness costs