Background choice as an anti-predator strategy: the roles of background matching and visual complexity in the habitat choice of the least killifish

Abstract

Because background matching improves concealment, prey animals have traditionally been expected to prefer parts of the habitat that match their visual appearance. However, empirical support for this is scarce. Moreover, this idea has recently been challenged by an alternative hypothesis: visual complexity of the background impedes prey detection, and hence prey could instead prefer complex parts of the habitat. We used the least killifish to test, with and without predation threat, for the importance of the visual similarity between the fish and the background, and the level of visual complexity of the background. We observed their choice between backgrounds patterned with elements based on the longitudinal black stripe of the fish. Predation risk was important under some circumstances, and induced a preference for a background of matching horizontal stripes compared with mismatching vertical stripes. Interestingly, females under predation threat showed a preference for a complex background of randomly oriented and overlapping stripes compared with matching stripes, whereas males did not discriminate between these two. Additionally, males showed a preference for matching stripes compared with complex shapes, whereas females did not discriminate between these backgrounds. We conclude that matching is important in the choice for safe habitat, but some aspects of visual complexity may override or act together with background matching.

Camouflage and Perceptual Organization in the Animal Kingdom

“…As a result, a camouflaged animal may be better concealed in more complex habitats independent of its match to the background (Merilaita et al 2001;Merilaita 2003;Dimitrova & Merilaita 2010). In line with this, there is recent evidence for animals choosing backgrounds that are not merely a good match to their own patterns, but are more visually complex (Kjernsmo & Merilaita 2012).…”

Background complexity and the detectability of camouflaged targets by birds and humans

“…While previous studies on nonhumans (e.g. [20][21][22]) show that search time increases when searching against a complex background, or animals (killifish Heterandria formosa) [23] have a preference for hiding in visually heterogeneous habitats, these studies lack any quantification of 'complexity'; analysis of what the features of any of the presumed distractors are that make search difficult, or whether the visual system codes different feature dimensions independently. In this experiment, we have shown that the application of metrics, particularly feature congestion, from machine vision, can provide insights to this question.…”

“…The latter has been investigated in laboratory experiments using artificially patterned prey and backgrounds, with birds [14,21,22] and fish [23]. There is value in replicating experiments on the effects of background complexity under more natural conditions; natural textures differ from the types of artificial textures used in these experiments in many ways, such as the contrast range and how deterministic or periodic the pattern is [24].…”

The Role of Life-History and Ecology in the Evolution of Color Patterns in Australian Chrysomeline Beetles

“…Nevertheless, background matching is especially important for individuals that are exposed while feeding (Pellissier et al, 2011;Kjernsmo and Merilaita, 2012), since the risk of predation can increase by up to a 100-fold (Bernays, 1997). One solution is for animals to have patches on the body surface with a mixture of contrasting colors or luminance that match different patches in the immediate adjacent surroundings (Pellissier et al, 2011;Wilts et al, 2012;Espinosa and Cuthill, 2014).…”