Group Size and Task Specialization in Ant Foundress Associations

Patricia Eck et al.

            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 and six foundresses of the ant species Messor pergandei into soil filled chambers and observed their performance of a single task, excavation.  We also placed groups of two and 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 the larger groups demonstrated significant specialization.  How I explain this best is by using the example of two people living in an apartment.  The carpet needs to be vacuumed, the dishes have to be done, the beds need to be changed and the rooms need to be dusted.  All tasks take energy, so the roommates share them all.  Then they decide to have two friends move in.  Now two of them can trade off vacuuming, one can do the dishes and one can change the sheets and dust.  They then decide to have two more friends move in.  Now two can still be trading off on the vacuuming, two can do the dishes, since now there are more dishes to be done, one can change the sheets on the beds and one can dust.  In other ant species specialization comes with a  significant survival cost; excavators often die.  However, in this species there was no significant correlation between the fourndress who excavated and foundress survival.  This suggests this species has evolved a system to distribute work effort more equitable among individual foundresses, offsetting negative costs of task specialization.