The dynamics of the daily round of the harvester ant colony ( Pogonomyrmex barbatus )

Colonies of the red harvester ant, Pogonomyrmex barbatus, do various tasks outside the nest. There is a daily temporal pattern in the numbers of ants engaged in each of five activities: foraging, nest maintenance, patrolling, midden work and convening. Perturbations were carried out in the field to investigate how the daily round changes in response to environmental events and colony needs. Interfering with nest maintenance, foraging or both caused changes in the temporal patterns in all five of the observed activities. Removing nest maintenance workers, foragers or both caused the numbers involved in all five activities to decrease, and there were temporal patterns in the effects of removals. The results of both interference and removal experiments show that the extent to which a worker group does one activity affects the behaviour of other groups. When nest maintenance or foraging is impeded experimentally, these two activities are of reciprocal priority. When both are impeded, foraging is of higher priority than nest maintenance. Harvester ants forage, patrol, maintain the nest area and foraging trails, collect and arrange pebbles on the nest, and gather in small groups, inspecting and grooming each other. The behaviour of the colony outside the nest at any moment can be described by citing the number of ants engaged in each of the five activities. The numbers change throughout the day in a predictable manner. There is a daily temporal pattern in the numbers of ants engaged in each activity. Describing the pattern in all activities is describing the daily round of the colony. Daily rounds are colony-specific (Gordon 1983a) and species-specific (Gordon 1984a), and response to experimental manipulations may depend on the stage in the daily round when experiments are done (e.g. Gordon 1983b). Thus, the daily round of a harvester ant colony provides a baseline from which to investigate colony behaviour. Certain aspects of chemical communication, response to new food sources and territorial behaviour can be explained in the context of the daily round (Gordon 1983b,c, 1984b). It would be a mistake, however, to think of the daily round as a rigid programme. Temporal patterns in the numbers of ants engaged in each activity can change. On some days, for example, foraging predominates; on others, colonies do mainly nest maintenance work (personal observation). The concept of the daily round is, loosely speaking, that of an equilibrium state, but the dynamics of colony organization are not yet understood. …