Scaling of recruitment with seed distribution and colony size in Pogonomyrmex

Ant colonies possess a “societal metabolism,” acquiring, transforming, and allocating resources through a network of foragers (Moses, 2005). Ant foraging- trail networks channel foragers to known food resources and away from competing colonies (Jun et al., 2003). Computer models suggest the spread of information occurs faster in larger colonies of harvester ants, genus Pogonomyrmex (Adler and Gordon, 1992), providing a possible mechanism of differentiation. Does the ability to utilize and share information scale super-linearly with a colony’s size? Within colonies, do foragers recruit more to denser sources of food, using information transfer to increase forager efficiency and harvest seed caches before competing colonies find them? To address these questions, we studied three sympatric species of Pogonomyrmex in central New Mexico that differ in average colony size: P. rugosus, P. maricopa, and P. desertorum. We hypothesized a) that across colonies recruitment to dense food resources scales positively with colony size, and b) that within colonies recruitment scales positively with seed density. We observed baited colonies for 1 hr, tracking the capture of dyed seeds arranged in piles of different densities and of native seeds. We generated a model of idealized effects of recruitment on foraging patterns and compared the output to our observations. We did not find support for hypothesis a, that recruitment scales positively with colony size, but did find support for hypothesis b, that recruitment does scale positively with increasing seed density. These findings highlight a key intersection between the metabolism of energy and of information.