Contrary to popular belief, stripes may not provide zebras or other animals that typically live in groups with any kind of protection from predators, researchers from the University of Cambridge reported Wednesday in the open-access scientific journal Frontiers in Zoology.
As part of their study, Anna Hughes, a Ph. D. student at Cambridge’s Department of Physiology, Development, and Neuroscience, and her colleagues recruited 60 different people to play a video game to test whether or not striped influenced their perception of moving targets.
The participants were asked to perform a task using a touch screen in which they tried to catch moving targets. One game had just one target on the screen, and another had multiple targets visible at the same time. When single targets were present, horizontal stripes targets were easier to capture those with vertical stripes, diagonal ones, or those uniform in color.
However, when there were several targets on screen at the same time, all of the striped targets, regardless of the direction of those stripes, were found to be more easily captured than uniform grey-colored targets. The findings appear to contradict the long-held assumption that stripes had evolved as a way to make it harder to capture group animals, the authors explained.
Findings call into question the effectiveness of ‘motion dazzle’
Hughes said that it was “surprising” that the striped targets “were easier to capture than a comparison grey target when the number of targets present was increased, as previous work has suggested that single striped targets are similarly difficult to catch to grey targets.”
“It’s not yet clear why this might be the case,” she told redOrbit via email. “One difference between our single target and multiple target games was that the single target game was time limited, whereas the subjects had as much time as they liked to catch all the targets in the multiple target game. So it could be that it’s only a very ‘split second’ effect. However, we’d obviously need to do more experiments to be able to say anything for certain.”
One might think that stripes and other high-contrast animals are more visible to predators, and in the past, researchers wondered if a concept known as “motion dazzle” could be used to explain why these markings evolved. Motion dazzle emphasizes the importance of movement, claiming that patterns cause predators to misread the speed and direction of a creature in motion, and that this phenomenon was strongest when creatures like zebra travelled in groups.
“The findings suggest that ‘motion dazzle’ effects may not be stronger and may even be weaker when multiple targets are present, which is surprising, as it is easy to imagine that stripes might be especially confusing and difficult to track in a large group,” Hughes explained. “Of course, this study is preliminary in many ways. Human eyes are different to those of the real predators of zebras, and therefore the effects of stripes on visual perception may also be different.”
“Similarly,” she added, “our model of group movement was very basic, with all the targets moving independently from each other: it may be the case that more complex designs, where the targets try to ‘stick together’ in the manner of a real herd would give a different result. Finally, the evidence for motion dazzle effects of stripes needs to be pieced together with the evidence for the other functions of the zebra’s distinctive pattern, as it is possible that the stripes have evolved for multiple purposes.”
(Image credit: Thinkstock)
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