The purpose of this experiment was to examine the effect of group size on division of labor in social groups. The ability of social groups to delegate tasks among specialists must depend in part on redundancy, or the number of individuals relative to the number of necessary tasks. Thus, we hypothesized that task specialization should increase with group size. To test this, we placed groups of two, four, or six foundresses of the ant species Messor pergandei into soil-filled chambers, and observed their performance of a single task, excavation. We additionally placed groups of two or six foundresses in observation nests, and monitored variation in performance of: surface excavation, tunnel excavation and brood care. We found that task specialization indeed increases with group size. The foundresses observed in pairs showed little specialization, while foundresses in groups of four and six both demonstrated significant specialization. In other ant species specialization is a significant survival cost; excavators often die. However, in this species there was no significant correlation between which foundress became the excavator and foundress survival. Our data suggest that this species has evolved a system to distribute work effort more equitably among individual foundresses, offsetting negative costs of task specialization.
Species 1: Hymenoptera Formicidae Messor pergandei (seed harvester ant)
Keywords: division of labor, social organization
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