Evidence for Apostatic Selection by Wild Passerines

Abstract

IT has been suggested that predators concentrate on common varieties of prey, and tend to overlook rarer forms even if they are obvious^1,2. Within a prey species this apostatic selection could act to maintain a balanced polymorphism^2,3. The selection would then be dependent on frequency in the sense that the selective value of each phenotype would vary inversely with its frequency^4,5. Direct evidence of such selection has been obtained from experimental studies of predation by fish², and there is indirect evidence of similar selection by birds^1,2,6. Ground-feeding passerines are important predators of many polymorphic insects and molluscs, and we report here some preliminary experiments designed to investigate their behaviour when presented with artificial dimorphic prey⁷.