Behavioral Flexibility and the Foraging Ecology of Seed-Eating Ants

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Abstract
Seed-eating ants are part of a guild of granivorous desert species that compete for food. This study examines the factors that influence the intensity, location, or temporal pattern of foraging in the red harvester ant, Pogonomyrmex barbatus. I consider behavioral flexibility on three time scales: year to year, day to day, and hour to hour. On a yearly time scale, there does not appear to be any simple relation between high intensities of foraging and survival rate. Colony-specific differences in foraging activity persist from one year to the next, but survivorship is not higher in colonies more likely to forage. Distributions of nests change from one year to the next and are usually underdispersed or clumped. Colonies live for 15-20 yr. Colony behavior is more stable, and more likely to avoid intraspecific conflict, in older colonies (> 5 yr old) than in younger ones (2 yr old). Mortality rates of 2-yr-old colonies are similar to those of older ones. Other results suggest that a colony's competitive status is determined by its behavioral flexibility in changing conditions, on daily and hourly time scales. Each day that a colony forages, it chooses a few foraging routes out of a larger set of available ones. This decision is made early each day by the patrollers, a distinct group of workers, before the foragers emerge from the nest. The choice of foraging trails is influenced by interactions with neighboring colonies. The extent to which neighboring colonies forage on trails that intersect, and engage in long-term conflict, depends on colony age and food availability. When there is a food incentive, pairs of neighboring younger colonies are more likely than older pairs to continue using foraging trails that overlap. On an hourly time scale, the intensity of foraging depends on the rate of food intake and on the activities of workers, such as patrollers, engaged in other tasks besides foraging.