THE INTENSITY OF INTERFERENCE VARIES WITH RESOURCE DENSITY - EVIDENCEFROM A FIELD-STUDY WITH SNOW BUNTINGS, PLECTROPHENAX-NIVALIS

Intake rates of snow buntings feeding on artificial seed patches were measured at different bird densities, for each of two different seed d ensities. Interference occurred in the low seed-density treatment, wit h intake rates declining at high bird densities. However, interference was not found in the high seed-density treatment. The finding that th e strength of interference may depend on resource density contradicts the hypothesis that the functional response is ratio-dependent (Arditi and Akcakaya 1990). The formulation for interference from Hassell and Varley (1969), and the models of Beddington (1975), Ruxton et al. (19 92) and Holmgren (1995), also assume that the strength of interference is independent of resource density. The development of behaviour-base d models that consider the relation between the intensity of interfere nce, resource density and individual state may provide a more accurate description of the process of interference.