The intensity of interference varies with food density: support for behaviour-based models of interference

Dolman (1995) measured the intake rates of snow buntings feeding on seed patches at difference bird densities, for each of two different seed densities. Interference occurred in the low food density treatment, with intake rate declining at high bird densities, but did not occur in the high food density treatment. Dolman states that existing models of the interference process assume that the intensity of interference is independent of food density. While this statement is true for the model of Hassell and Varley (1969), we show that behaviour-based models of interference do not assume that interference is independent of food density. We examine two simple analytic behaviour-based models of interference and show that, in agreement with Dolman's observations, intensity of interference is predicted to decrease with increasing food density. Dolman plotted log (intake rate) against log (bird density). Rather than obtaining a linear relationship predicted by the Hassell and Varley model, the results from the low seed density treatment indicated a curvilinear relationship consistent with those produced by our behaviour-based models. These results provide support for the use of behaviour-based models of interference over the model of Hassell and Varley.