A new research suggests that zebra stripes are very unlikely to have evolved in an effort to help the animals evade predators. But what other explanation could there be?
Over the years, there have been various hypotheses about the purpose of zebra stripes – which have long been a mystery. Some of these include: protection against predators and disease-carrying insects, social cohesion, and control of body temperature.
The new research – published Friday (Jan. 22) in the journal PLOS ONE – states that zebra stripes could not have evolved to provide camouflage. That is because at the distance where the stripes can be spotted by predators, they have probably already smelled, heard or seen their prey.
Tim Caro, co-author of the study and a professor of wildlife biology at University of California Davis (UC Davis), said that the end-results do not provide any support for the idea the zebra stripes have an anti-predator camouflage effect.
For the research, scientists passed digital images taken in Tanzania through colour and spatial filters. With this technique they stimulated how hyenas, lions, and zebras themselves, would see the stripes. The scientists also measured the contrast and width of the stripes, which helped them figure out how far a lion, hyena, or zebra would have to be to still be able to detect the stripes under daylight, twilight, or on a moonless night.
Amanda Melin, lead author of the study and an assistant professor of biological anthropology at the University of Calgary, Canada, stated that until now the camouflage hypothesis has always been framed through human eyes.
The final results showed that the stripes are difficult for large carnivores to see when they are situated beyond about 164 feet (fifty metres) from the zebras in daylight and about 98 feet (thirty metres) at twilight. The distance decreases to approximately 29 feet (nine metres) during moonless nights, the scientists found.
Moreover, the scientists also concluded that lions were able to see the outlines of zebras on open plains just as easily as those of other smaller prey.
Brenda Larison, an Assistant Researcher at the UCLA Center for Tropical Research and Department of Ecology and Evolutionary Biology, said that one possible hypothesis as to why zebras have stripes would be temperature – which can predict the amount of stripe pattern variations. However, this research was unable to determine the exact correlation between stripes and temperature.
Another explanation could be that stripes help zebras protect themselves against flies, according to Dr. Daniel Rubenstein of Princeton University.
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