Colour polymorphism and selective predation experiments

Abstract

The significance of searching-image behaviour by predators in relation to visually polymorphic prey is outlined in relation to its possible role in maintaining these polymorphisms by frequency-dependent selection. A simple experimental design is described whereby innate preferences, selection for crypsis, and searching-image behaviour can be distinguished. Four experimental situations are described ranging from an artificial predator-prey relationship (humans as predators—dyed toothpicks as prey) to a semi-natural one (wild song thrushes as predators—artificial populations of live polymorphic snails as prey). The results suggest that “naive” predators may regularly form searching-images for a frequent prey type.