Motion dazzle and camouflage as distinct anti-predator defenses
ABSTRACT Camouflage patterns that hinder detection and/or recognition by antagonists are widely studied in both human and animal contexts. Patterns of contrasting stripes that purportedly degrade an observer's ability to judge the speed and direction of moving prey ('motion dazzle') are, however, rarely investigated. This is despite motion dazzle having been fundamental to the appearance of warships in both world wars and often postulated as the selective agent leading to repeated patterns on many animals (such as zebra and many fish, snake, and invertebrate species). Such patterns often appear conspicuous, suggesting that protection while moving by motion dazzle might impair camouflage when stationary. However, the relationship between motion dazzle and camouflage is unclear because disruptive camouflage relies on high-contrast markings. In this study, we used a computer game with human subjects detecting and capturing either moving or stationary targets with different patterns, in order to provide the first empirical exploration of the interaction of these two protective coloration mechanisms.
Moving targets with stripes were caught significantly less often and missed more often than targets with camouflage patterns. However, when stationary, targets with camouflage markings were captured less often and caused more false detections than those with striped patterns, which were readily detected.
Our study provides the clearest evidence to date that some patterns inhibit the capture of moving targets, but that camouflage and motion dazzle are not complementary strategies. Therefore, the specific coloration that evolves in animals will depend on how the life history and ontogeny of each species influence the trade-off between the costs and benefits of motion dazzle and camouflage.
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ABSTRACT: Background Stripes and other high contrast patterns found on animals have been hypothesised to cause ¿motion dazzle¿, a type of defensive coloration that operates when in motion, causing predators to misjudge the speed and direction of object movement. Several recent studies have found some support for this idea, but little is currently understood about the mechanisms underlying this effect. Using humans as model `predators¿ in a touch screen experiment we investigated further the effectiveness of striped targets in preventing capture, and considered how stripes compare to other types of patterning in order to understand what aspects of target patterning are important in making a target difficult to capture.ResultsWe find that striped targets are among the most difficult to capture, but that other patterning types are also highly effective at preventing capture in this task. Several target types, including background sampled targets and targets with a `spot¿ on were significantly easier to capture than striped targets. We also show differences in capture attempt rates between different target types, but we find no differences in learning rates between target types.Conclusions We conclude that striped targets are effective in preventing capture, but are not uniquely difficult to catch, with luminance matched grey targets also showing a similar capture rate. We show that key factors in making capture easier are a lack of average background luminance matching and having trackable `features¿ on the target body. We also find that striped patterns are attempted relatively quickly, despite being difficult to catch. We discuss these findings in relation to the motion dazzle hypothesis and how capture rates may be affected more generally by pattern type.BMC Evolutionary Biology 09/2014; 14(1):201. DOI:10.1186/s12862-014-0201-4 · 3.41 Impact Factor
Article: The function of zebra stripes.[Show abstract] [Hide abstract]
ABSTRACT: Despite over a century of interest, the function of zebra stripes has never been examined systematically. Here we match variation in striping of equid species and subspecies to geographic range overlap of environmental variables in multifactor models controlling for phylogeny to simultaneously test the five major explanations for this infamous colouration. For subspecies, there are significant associations between our proxy for tabanid biting fly annoyance and most striping measures (facial and neck stripe number, flank and rump striping, leg stripe intensity and shadow striping), and between belly stripe number and tsetse fly distribution, several of which are replicated at the species level. Conversely, there is no consistent support for camouflage, predator avoidance, heat management or social interaction hypotheses. Susceptibility to ectoparasite attack is discussed in relation to short coat hair, disease transmission and blood loss. A solution to the riddle of zebra stripes, discussed by Wallace and Darwin, is at hand.Nature Communications 02/2014; 5:3535. DOI:10.1038/ncomms4535 · 10.74 Impact Factor
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ABSTRACT: In 1909, Abbott Thayer suggested that the study of animal coloration lies in the domain of artists because it deals with optical illusions. He proposed, for example, that prey color patterns may obliterate the animal's outline to make the wearer appear invisible to its preda-tors. Despite a long history of research on the neuropsychology of visual illusions in humans, the question of whether they can occur in other animals has remained largely neglected. In this review, we first examine whether the visual effects generated by an animal's shape, coloration, movement, social environment, or direct manipulation of the environment might distort the receiver's perspective to form an illusion. We also consider how illusions fit into the wider conceptual framework of sensory perception and receiver psychol-ogy, in order to understand the potential significance of these (and other) visual effects in animal communication. Secondly, we con-sider traits that manipulate visual processing tasks to intimidate or mislead the viewer. In the third part of the review, we consider the more extreme cases of sensory manipulation, in which individuals or their traits disrupt, overstimulate, or inactivate receivers' sensory systems. Although illusions present just one form of sensory manipulation, we suggest that they are likely to be more common than previously suspected. Furthermore, we expect that research in this area of sensory processing will provide significant insights into the cognitive psychology of animal communication.Behavioral Ecology 01/2014; 25(3):450-463. DOI:10.1093/beheco/art118 · 3.16 Impact Factor