BETWEEN INEFFICIENCY AND INTERFERENCE: INDIVIDUAL AND COLLECTIVE EFFECTIVENESS OF PROBLEM RESOLUTIONS IN LEAF-CUTTING ANTS
Andrea Marina Alma, Alejandro Gustavo Farji-Brener , Luciana Elizalde
Laboratorio Ecotono INIBIOMA-UNComahue; Laboratorio Ecotono INIBIOMA-UNComahue ; Laboratorio Ecotono INIBIOMA-UNComahue
One advantage of social organisms is their option to individually or collectively resolve situations that alter the normal progress of an activity (hereafter, problems). Using the trail cleaning behavior of leaf-cutting ants, we evaluated a conceptual model according to which cleaning strategies depend on obstacle size and shape, foragers flux and trail irregularities because efficacy and efficiency of each strategy vary differently with the characteristics mentioned before. We placed obstacles of different sizes and shapes, in different ant flux conditions and in smooth or irregular trails in 10 field nests of Atta cephalotes, and compared the proportion of successful removals and the removal time, as estimators of efficacy and efficiency, respectively, of removals made by one or two-three workers. We found that very large obstacles could only be removed collectively which might be a consequence of individual limitations for transporting big objects. Regardless of the obstacles shape, collective removals had higher efficacy but lower efficiency than individual removals. This might be a consequence of the need of coordination among individuals participating in the collective removals. Furthermore, whatever the ant flux, ants were less efficient collectively than individually, but as the ant flux increased, the efficacy increased for collective removals and decreased for individual removals. One explanation for this pattern is the strength required to remove an obstacle through a high density flux. Finally, trail irregularities similarly affected the efficacy and efficiency of individual and collective removals. This work highlights one of the advantages of social organisms, the option of resolving collectively those problems that exceed the individual abilities, and its associated costs: the need of coordination among society members to make a joint action.