This investigation compares the energy budgets of three species of Pogonomyrmex harvester ants along an altitudinal transect in southern California. All three demonstrate similar seasonal patterns, with high foraging activity and high respiratory costs in mid-summer and little or no activity during winter. Respiration, predominantely metabolism of the workers, was estimated to account for 84–92% of the energy assimilated by the nests. The remaining 8–16% of the energy was invested in the production of new individuals. However, total production was not correlated with food input. It is suggested that worker care of the brood may be the most important determinant of brood production, and thus food may not be a direct limiting resource in harvester ants.
A higher percentage of production is invested in workers than in reproductives in all three species. The species usually partition similar proportions of energy between the production of males and females, but since females are larger, more males are produced. Although the species are in different habitats and have very different numbers of workers per nest, the numbers of sexuals produced per nest are similar. The sex-ratio appears to be ecologically determined. Nests that were provided with additional food invested more energy in the production of males. Control nests, nests which had food removed and older nests invested more in the production of females or invested equally in the production of the two sexes.