A comparison of the energy budgets of three species of Pogonomyrmex harvester ants (Hymenoptera: Formicidae)

Abstract

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.

How colony growth affects forager intrusion between neighboring harvester ant colonies

“…Brian 1973;Porter and Tschinkel 1985). Much of the energy assimilated by adult ants in Pogonomyrmex colonies is spent by workers engaging in activities related to brood care [about 60% in P. rugosus; about 30% goes directly to feed larvae (MacKay 1985)]. A colony's demand for food may depend on the number of immature ants to be raised, relative to the numbers of adult workers available to care for brood, collect and process food, and feed it to larvae (Schneirla 1971 ;Topoff and Mirenda 1980).…”

“…); large, presumably older colonies have been observed to produce large numbers of reproductives (H611dobler 1976). MacKay's (1985) physiological studies show that much more energy is devoted to the production of workers than of reproductives in several Pogonomyrmex species. Further work is needed to investigate how a colony's territorial behavior depends on the relation between the number of workers and alates being produced, and the numbers of workers available to feed and care for them.…”

Harvester ant nests, soil biota and soil chemistry

“…Workers mill seeds within the nest, and deposit considerable amounts of cha on the surface in midden piles located within about 1 m of the nest entrance. A related species with similar dietary habits, P. rugosus, discards over 60% of the total energy collected by foragers onto the midden (MacKay 1985). Clipped vegetation and dead ants are sometimes also deposited on the midden, but ant carcasses are usually removed by other arthropod scavengers.…”

Provisioning behavior and the estimation of investment ratios in a solitary bee, Calliopsis (Hypomacrotera) persimilis (Cockerell) (Hymenoptera: Andrenidae)

“…This is probably because male offspring gain less weight per unit of provisions than female offspring. Studies of metabolic rate in ants have shown that males have higher metabolic rates than females (Peakin 1972;Boomsma and Isaaks 1985;MacKay 1985).…”