DESPOTIC BEHAVIOR AND THE EVOLUTION OF MIGRATION PATTERNS IN BIRDS

The despotic distribution described by Fretwell and Lucas (1970) and the ideal free distribution of individuals differing in competitive ability (Parker and Sutherland 1986) were applied to the evolution of migration patterns. In both theories, dominant individuals monopolize the best resources but dominance is mediated by prior occupancy in the former and by body size in the latter. Additional parameters used were latitudinal suitability gradients for both breeding and wintering, and costs of migration between sites. When migration costs are high, leap-frog migration is the most likely pattern to develop, Chain migration develops when either of two intricate conditions are fulfilled: (1) Both the breeding and the wintering suitability gradients increase towards the north and dominance is due to body size. (2) Breeding suitability increases towards the north and wintering suitability towards the south and dominance is due to prior occupancy. Under special circumstances, no stable pattern is likely to develop.