Apostatic selection by blue jays produces balanced polymorphism in virtual prey

Abstract

Apostatic selection, in which predators overlook rare prey types while consuming an excess of abundant ones, has been assumed to contribute to the maintenance of prey polymorphisms1,2,3. Such an effect requires predators to respond to changes in the relative abundance of prey, switching to alternatives when a focal prey type becomes less common4,5. Apostatic selection has often been investigated using fixed relative proportions of prey1,6, but its effects on predator–prey dynamics have been difficult to demonstrate7. Here we report results from a new technique that incorporates computer-generated displays8,9 into an established experimental system, that of blue jays (Cyanocitta cristata) hunting for cryptic Catocala moths10. Digital prey images from a virtual population are presented to predators. The relative numbers that escape detection determine the subsequent abundance of each prey type. If apostatic selection does promote stability, the system should converge on an eqlibrium in which each prey type appears at a characteristic abundance. Our results show that the detection of cryptic prey does involve apostatic selection, and that such selection can function to maintain prey polymorphism.