Tinbergen hypothethized that the birds
needed a certain number of chance encounters with novel prey to be able to form a search image for them. Inherent in this idea was the concept that detection of prey represents a sensory ‘problem’, and hence the search image is typically considered only to facilitate prey detection when prey are cryptic (Tinbergen, 1960; Dawkins, 1971; Lawrence & Allen, 1983; Dukas, 2002). It has been demonstrated that the formation of a search image is a result of selective attention after a sequential exposure to a particular stimulus (Croze, 1970; Bond & Riley, 1991; Blough, 1992; Reid & Shettleworth, 1992; Langley, 1996; Bond & Kamil, 1999; Dukas & Kamil, 2001). A predator
forming a search image will focus on certain features of a frequently encountered prey type that enable it to detect the prey more efficiently, but this PD-0332991 supplier focus will interfere with the detection of other types of prey that lack the appropriate features (Kamil & Bond, 2006). When the more common prey type becomes rare, ‘perceptual switching’ is predicted to occur (Bond, 2007) as a new search image is formed after a series of consecutive detections of what is now the most abundant prey type. This change in search image is what produces the actual switch in predation levels on different prey types. Apostatic selection has primarily been studied in the context of PI3K inhibitor colour polymorphisms in invertebrates, where the main agent of selection has been assumed to be predation by birds. The fact that birds are easily trained to perform specific tasks in experimental conditions, and that they prey upon colour-polymorphic invertebrates with low mobility (e.g. snails), facilitates the study of patterns that are consistent MCE公司 with apostatic selection. In order to demonstrate that apostatic selection occurs, and is capable of maintaining balanced polymorphisms, it is
first necessary to establish that predators that feed on polymorphic prey show perceptual switching. This has been demonstrated in laboratory free-choice experiments such as the one carried out by Bond (1983), in which he presented different types of grain on two kinds of background where they were either cryptic or conspicuous to pigeons. The pigeons showed a preference for the more common grain on the cryptic background. The effect was lost when the grains were conspicuous. The response rate was reduced as the relative proportions of grain types became equal, which Bond explained could indicate a decrease in searching efficiency owing to repeated switching from one grain type to another. Other laboratory free-choice experiments have supported the occurrence of perceptual switching (Cooper, 1984; Tucker, 1991; Reid & Shettleworth, 1992; Cooper & Allen, 1994).