Supporting the “roof of the world” (Image: XI ZHINONG/naturepl.com)
By Fred Pearce, New Scientist.Com
The plateau pika doesn’t have many friends. This small burrowing relative of the rabbit, weighing only around 140 grams, is the most abundant mammal on the vast grasslands of the Tibetan plateau, but it is widely condemned as a cause of soil erosion and an ecosystem wrecker. There is a government-funded campaign to exterminate them by poisoning their burrows all across the flatlands, also known as the “roof of the world”.
But the tide could be turning. Recent studies have found that the pika is not a pest after all, but a “keystone species”. It is being recast as protector of the 2.5 million square kilometres of grasslands across Tibet. It could be essential for supporting birds of prey and the Tibetan fox, as well as being a vital ecological engineer, affecting the flow of water to some of the planet’s largest rivers.
Pika poisoning is government policy in China. Each winter, teams of workers soak grain in Clostridium botulinum, a bacterium that produces the neurotoxin botulinum, and stuff it down pika burrows. In many areas, this assault is now eliminating the animal, says Andrew Smith of Arizona State University in Tempe. “You can drive for hundreds of kilometres across the plateau and fail to see a single pika,” he says.
This pogrom is damaging the many species that prey on the plateau pika. According toRichard Harris of the University of Montana animals such as buzzards are suffering, as well as the Tibetan fox, which has an almost identical territory to the pika and is found nowhere else. His detailed study of fox scat revealed for the first time that the fox is almost entirely dependent on the pika for food. It turns out that no pika will mean no foxes, too.
Pika pogrom
And there is more to these rabbit relatives than just being food to larger species. The Tibetan plateau has been called Asia’s water tower, and it is where giant rivers such as the Yangtze, Mekong, Indus and Yellow River originate. Smith found that soils in areas where pika are still at large hold more water. This is down to their burrowing behaviour, which mixes the wetter top layer with dryer soil deeper down. By holding more water, the soil reduces surface run-off that can cause floods.
Exterminating the pika means the poisoners are making the rivers downstream more flood-prone in the wet season, and more likely to dry up at other times, Smith argues.
Chinese researchers, led by Lü Zhi, director of the Center for Nature and Society at Peking University, lobbied state officials in December to end the extermination campaign, arguing that the pika is not a pest but a vital element of a fragile ecosystem. Smith is hopeful that the new evidence and campaign to save the pika will deliver.
“Maybe change is in the air,” says Smith.
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