Seasonal worker demography shapes colony-level labor allocation in the Florida harvester ant (Pogonomyrmex badius)

The proportions of workers attending to tasks must change in order for an ant colony to function efficiently throughout its ontogeny and during each annual cycle. In species that exhibit temporal polyethism, it is possible for selection acting at the level of the colony to favor age-frequency distributions that optimize colony productivity. Annual patterns of forager allocation were measured over a three year period for 43 colonies of the Florida harvester ant (Pogonomyrmex badius). Colonies exhibited a consistent pattern of allocation across years, with the largest proportion of workers aging into the role of forager at the peak of sexual larvae production. The percent of each colony allocated to foraging was shown to increase in spring, due in part to a reduction in colony size resulting from forager death without larval replacement, as well as an increase in forager population size. The decrease in percent foraging which followed, resulted from an increase in colony size through new worker birth. To investigate the mechanisms P. badius colonies use to generate the observed allocation patterns, colony responses to an experimental increase in larval population size and a reduction in forager population size were measured. In experimental colonies, removed foragers were not replaced after one week’s time; indicating that worker age, not colony demand may be responsible for the annual patterns of labor allocation in P. badius.