Magazine article Natural History

Cooling Stripes

Magazine article Natural History

Cooling Stripes

Article excerpt

Why zebras have stripes has long perplexed naturalists and continues to challenge scientists. Among the proposed explanations are that stripes promote social cohesion, regulate temperature, or confuse predators and biting flies. The matter, however, is far from settled.

Ecologist Brenda Larison of the University of California, Los Angeles, and six colleagues decided to have a fresh look at three hypotheses: predator evasion, thermoregulation, and biting fly avoidance. Plains zebras, Equus quagga, show a marked geographic variation in their stripes, which range from heavy black-and-white patterns covering the entire body to thinner, lighter stripes restricted to particular areas. For example, a now extinct subspecies from South Africa, E. q. quagga, had stripes on its neck, head, and torso but not on its belly or legs. The difference from region to region prompted the team to search for associations between environmental factors and striping patterns.

The researchers chose sixteen populations of plains zebras and photographed a minimum of eight animals per site. Using image-processing software, The noted then number of stripes and their length, thickness, and color saturation on the legs, torso and belly. They also gathered data on twenty-nine environmental variables, including temperature, precipitation, soil moisture, leaf water content, and tree canopy cover. In addition, they used the Food and Agricultural Organization's published distribution of tsetse flies and modeled the historic geographic distribution of lions and tsetse flies. …

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