The structure of foraging activity in colonies of the harvester ant, Pogonomyrmex occidentalis

The timing of activity by desert dwelling poikilotherms can be critical to survival. In the western harvester ant, colonies that have higher levels of genetic diversity forage for longer time periods in the morning than colonies with less diversity. We determined whether the advantage of early foraging colonies was consistent by examining foraging behavior at other times of day and year. We used a combination of activity monitoring and temperature measurement at the nest entrance to quantify foraging activity during the morning and evening summer foraging periods in both June and August. The duration of morning and evening foraging was significantly positively correlated both within and across seasons—some colonies have a consistent advantage in foraging. The temperature range over which colonies foraged was also consistent across time, suggesting that intercolony differences are a consequence of variation in the thermal ranges/preferences of the colony's workers. The duration of foraging during this study was correlated with the duration of foraging measured 6 years earlier, suggesting that it is an aspect of colony phenotype.