DESPOTIC BEHAVIOR AND THE EVOLUTION OF MIGRATION PATTERNS IN BIRDS

The despotic distribution described by Fretwell and Lucas (1970) and t he ideal free distribution of individuals differing in competitive abi lity (Parker and Sutherland 1986) were applied to the evolution of mig ration patterns. In both theories, dominant individuals monopolize the best resources but dominance is mediated by prior occupancy in the fo rmer and by body size in the latter. Additional parameters used were l atitudinal 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) Bo th the breeding and the wintering suitability gradients increase towar ds the north and dominance is due to body size. (2) Breeding suitabili ty increases towards the north and wintering suitability towards the s outh and dominance is due to prior occupancy. Under special circumstan ces, no stable pattern is likely to develop.