Date of this Version
Southwestern Naturalist (November 23, 1988) 33(4).
Little is known about the life span of individual ant colonies (Keeler, 1981), even though the dynamics of some species, such as harvester ants, are crucial to the structure of plant and animal communities (e.g., Brown et al., 1979). This note reports the results of 10 years of observations on a population of harvester ants.
Fifty-six mounds of Pogonomyrmex occidentalis Cresson (Hymenoptera: Formicidae), western harvester ant, were permanently marked with aluminum tags in August 1977. The site, about 1 ha just south of the University of Nebraska's Cedar Point Biological Station, Keith Co., Nebraska, was within a pasture subject to moderate, half-summer grazing. The vegetation was typical shortgrass prairie, dominated by buffalo grass (Buchloe dactyloides) and hairy and smooth grama grasses (Bouteloua hirsuta and Bouteloua gracilis) interspersed with needle-and-thread grass (Stipa comata) and forbs such as Yucca glauca (Kaul et al., 1983). Each August from 1977 to 1987, the population was censused, deaths noted and new colonies marked.
Of 56 colonies marked in 1977, 45 were still alive in 1986, which is an average death rate of 0.02 colonies/year. If one assumes a stable population in which recruitment balances mortality, this survival of 80.3% over a decade implies a life expectancy, for an established colony, of 50.9 years.