Natural levels of colour polymorphism reduce performance of visual predators searching for camouflaged prey

Abstract

Polymorphism, the coexistence of two or more variants within a population, has served as a classic model system to address questions about the evolution and maintenance of intraspecific variation. It has been hypothesized that a natural level of colour polymorphism may impair the search efficiency of visually orientated predators. To test this polymorphism protects hypothesis, we asked human participants to search for images of natural black, striped or grey Tetrix subulata grasshopper colour morphs presented against photographs of their natural habitat on computer screens. Fewer grasshoppers were detected when morphs were presented in mixed than in uniform sequences. All three morphs benefited to comparable degrees, in terms of reduced detection, from being presented in polymorphic sequences. Our findings demonstrate that natural levels of polymorphic variation can impede the efficiency of visually orientated predators and increase survival of prey. This protective effect supports the limited attention hypothesis, explains why predators develop 'search images', may account for the spread and establishment of novel colour variants, and contributes to maintenance of polymorphisms.

Both novelty and conspicuousness influence selection by mammalian predators on the colour pattern ofPlethodon cinereus(Urodela: Plethodontidae)

“…Previous research suggests that bird predators select P. cinereus coloration such that erythristic individuals evolve coloration that is similar to N. viridescens (Brodie & Brodie, 1980;Tilley et al, 1982;Kraemer & Adams, 2014). Research on other taxa has likewise found support for frequency-dependent selection (Pfennig et al, 2007;Karpestam, Merilaita & Forsman, 2014), though under different mechanisms (i.e. This complex selective regime may have contributed to the initial evolution of the erythristic colour morph, with mammal predators avoiding such a novel morph, while birds avoided the erythristic morph because of its similarity to N. viridescens.…”

Improved camouflage through ontogenetic colour change confers reduced detection risk in shore crabs

“…Our results also showed that the crabs developed more uniform patterning (see also Figure S2). It is not well known what maintains the high colour variation in juvenile crabs, but it may be related to the need to match variable background habitats at spatial scales (Nokelainen, Hubbard et al, ) that are relevant when individuals are small, and/or breaking predator search image formation (Bond & Kamil, ; Duarte et al, ; Karpestam et al, ; Punzalan et al, ). It is plausible that juvenile crabs may also rely on other types of camouflage, such as disruptive coloration (Todd et al, ), and this may be habitat‐specific, with crabs from rock pools favouring disruption and crabs from mudflats tending towards background matching.…”

Camouflage

“…A learnt conjunction of features in an otherwise cryptic prey, resulting in a short‐term perceptual filter through selective attention, is what biologists describe as a ‘search image’ (Allen, ; Langley, ). The fact that search image formation improves detection of frequently encountered prey at the expense of reduced detection of infrequent prey (Pietrewicz & Kamil, ; Reid & Shettleworth, ; Plaisted & Mackintosh, ) does indeed favour polymorphism in prey appearance (Bond & Kamil, ; Karpestam, Merilaita & Forsman, ). That said, because some types of camouflage pattern seem to be easier to learn than others (Troscianko et al ., ; Troscianko, Skelhorn & Stevens, ), the polymorphism may be constrained in ways that are as yet not fully understood.…”