INTERFERENCE COMPETITION IN CENTRAL PLACE FORAGERS - THE EFFECT OF IMPOSED WAITING ON PATCH-USE DECISIONS OF EASTERN CHIPMUNKS, TAMIAS-STRIATUS

When central place foragers compete aggressively for patchy resources, subordinates may be prevented from collecting food until a dominant h as departed with its load. Extensions of central place foraging models predict that animals forced to wait at a patch should increase their load sizes and patch times as well as their tendency to search for and switch to alternative patches. We tested these predictions using east ern chipmunks, Tamias striatus, hoarding sunflower seeds collected fro m seed/vermiculite mixtures in trays placed 5-8 m from their burrows. By using her hand to prevent access to the patch, the experimenter sub jected animals to progressively increasing waiting times at two seed d ensities; another series of trials at the same seed densities monitore d a similar number of trips without imposed waiting. As predicted, pat ch times and load sizes were higher in sessions with imposed waiting t han in control sessions. Load sizes increased with trial number in exp erimental sessions but decreased or remained the same in control sessi ons. Chipmunks spent more of their time searching for alternative patc hes during trials with imposed waiting than during controls. They also started searching for alternative patches at lower levels of imposed waiting when using poor than when using rich patches. These results in dicate that the effects of interference on foraging decisions and on s patial overlap between individuals can be predicted by simple economic models. Furthermore, the results suggest how resource-defense tactics can be predicted by the economic effects of interference on the forag ing efficiency of the opponent. Key words: central place foraging, chi pmunk, competition, environmental tracking, hoarding, interference, lo ad size, optimal foraging, patch choice, resource defense, Sciuridae, Tamias striatus.