Interference and the ideal free distribution: Models and tests

We review the assumptions and predictions of five competitive distribution models that predict how optimal foragers will be distributed across resource patches when gains are reduced by interference. This review revealed a number of previously ignored predictions and assumptions: in particular, there should be no change in relative patch use as competitor density changes. A new model is proposed in which interference results from the costs of encounters with other foragers and where the gains on a patch are independent of the costs of interference. This model predicts that as density increases, there will be increased proportional use of lower-quality patches. Past empirical studies of interference distributions are reanalyzed; none of the studies provides strong support for any of the existing ideal free-distribution models. We suggest that previous results are more consistent with the predictions of our new model.