Group choice: competition, travel, and the ideal free distribution

If a group of foragers distributes among resource patches according to the ideal free distribution, the relative number of foragers in each patch should match the relative amount of resource obtained there, unless deviations arise from factors such as incomplete information or interforager interference. In analogy to individual choice, such effects may produce undermatching—group distribution falling short of resource distribution—or overmatching—group distribution overshooting resource distribution. In the present experiments, a flock of about 30 pigeons distributed between two patches with continuous inputs of green peas. Competition was varied by changing the size or extent of the patches. When the patches were areas or troughs, some undermatching occurred. When the patches were small bowls, strong undermatching occurred. When travel was required to switch patches, undermatching decreased slightly. A visual barrier that prevented pigeons from seeing one patch from the other had no effect. Overall rate of food delivery, varied over a wide range, had no effect. It appeared that the mechanism of flock distribution depended on comparisons between patches that were successive rather than simultaneous. Although most pigeons participated in the experiments, and different pigeons participated to different extents, individual pigeons tended to be consistent in the extent of participation from session to session, suggesting the possibility that participation might reflect competitive ability. Examination of the preferences and switching of individual pigeons revealed no consistency within or across individuals. It appeared that the flock's distribution was a truly emergent phenomenon, in the sense that results at the level of the flock in no way paralleled behavior at the level of the individual.