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Why do zebras have stripes?

Release date:2016-01-27

 

A new study suggests that it is highly unlikely that the Zebras' stripes have evolved in an effort to provide camouflage【伪装】, Christian Science Monitor reports.


"The results from this new study provide no support at all for the idea that the zebra's stripes provide some type of anti-predator【反捕食者】 camouflaging effect," said co-author Tim Caro, UC Davis wildlife biology professor.


"Instead, we reject this long-standing hypothesis that was debated by Charles Darwin and Alfred Russell Wallace."


Various hypothesis have been put forward to explain the purpose of zebras' stripes, including "confusing predators, protecting against disease-carrying insects, controlling body temperature and social cohesion【社会凝聚力】".


For the study, the researchers took digital images from a field in Tanzania and simulated how zebras' main predators, lions and hyenas【土狼】, as well as zebras themselves, would perceive the stripes.


They also measured the stripes' width and contrast, and drew conclusions based on the knowledge of various animals' visual capabilities.


"The most longstanding hypothesis for zebra striping is crypsis【保护色】, or camouflaging, but until now the question has always been framed through human" said lead author Amanda Melin, assistant professor of biological anthropology at the University of Calgary, Canada.


"We, instead, carried out a series of calculations through which we were able to estimate the distances at which lions and spotted hyenas, as well as zebras, can see zebra stripes under daylight, twilight, or during a moonless night."


Results from the study suggested that the stripes are difficult for large carnivores【食肉动物】 to distinguish beyond 50 meters (about 164 feet) in daylight or 30 meters (about 98 feet) at twilight, and a mere 9 meters (about 29 feet) on moonless nights.


Also, in open fields, lions could see the outline of zebras just as easily as that of similar-sized prey with fairly solid shading patterns.


One hypothesis, published in January 2015, suggests that "temperature successfully predictsa substantial amount of the stripe pattern variation observed in plains zebra".


There is also research in support of zebras' stripes helping to deter【制止】 biting flies.


 "And lastly, moving zebras are thought to dazzle and confuse attacking predators in part by creating optical illusions", says Rubenstein. "So far support for this hypothesis is mixed and has come mostly from computer studies in which human subjects attempt to hit striped and unstriped moving objects."  


"Clearly, more study is needed to evaluate the relative importance of each of these alternatives."



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