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  3. An annual census of wolves at Yellowstone National Park has found a sharp drop in the population. But park biologists, who suspe

An annual census of wolves at Yellowstone National Park has found a sharp drop in the population. But park biologists, who suspe

admin2010-06-17  100
问题     An annual census of wolves at Yellowstone National Park has found a sharp drop in the population. But park biologists, who suspect a deadly disease, canine parvovirus, say they will let nature take its course. "Parvo can be vaccinated for and can be treated, but we wouldn’t do it because we couldn’t catch every animal", Daniel Stahler, a park waif biologist, said, "And this allows them to build up a natural resistance".
    The census found 22 pups, compared with 69 last year. The total count of wolves dropped m 118 from 171, the lowest since 2000. "It was somewhat devastating to have such poor pup survival", Mr. Stahler said. "But research shows that young pups can bounce back from it quite successfully". That pups have suffered the decline seems to suggest the culprit is parvo, said Ed Bangs, waif recovery coordinator for the United States Fish and Wildlife Service here. Nursing pups receive immunity from their mother’s milk. but the immunity drops when nursing stops.
    The large number of wolves in the park might also be a factor. "When you have a big litter and adults are having trouble killing enough to feed all these pups, and the animals are stressed, parvo flares up", Mr. Bangs said. "If you have 15 brothers and sisters instead of 3, you don’t get enough to eat; parvo kills you".
    Canine parvovirus was discovered in the United States in 1978. Extremely hardy, the disease spread rapidly to domestic dogs and then into wild animal populations. Biologists suspect that it was introduced to Yellowstone by a tourist’s infected dog or a coyote. Because parvo is so hardy, it persists in the soil for months. A wolf could catch it from simply sniffing infectious soil. the biologists said. The disease has hit wolves on the northern range, the elk-filled meadows of the northern half of the park, especially hard. Out of 49 pups born there, 8 survived.
    Some scientists, including Mr. Bangs, theorize that the park may have overshot its capacity for wolves and that the numbers are naturally adjusting downward, with disease being one of the agents. The long-term carrying capacity of the park, he said, is probably 110 to 150 wolves.
    Wolves have been killed in other ways, too. Frequent encounters among competing wolf packs are the biggest cause of death among adults. In the first five years of their reintroduction to the park, one or two animals a year were killed by other wolves. That number has risen to four or five a year.
    Vehicles also take a toll, Fourteen wolves have been killed by vehicles in the last 10 years, eight of them near Mile Marker 30 on Route 191, a straight stretch on the western side of the park where motorists tend to speed and wolves are plentiful.
选项 A、they will vaccinate the wolves
B、they have no method to deal with the disease
C、they will build up a natural resistance
D、they will not take any measure
答案D
解析 推理判断题。原句是"But park biologists, who suspect a deadly disease, canine parvovirus, say they will let nature take its course."根据下文，治疗这种疾病有疫苗，但是公园不会给狼注射，这样做一是因为不可能抓住每只狼，二是这样有利于狼建立起自然抵抗力。"let nature take its course"字面意义是"让自然按其常规运行"，根据前后文，这里就是说不采取任何措施，让自然来决定狼的生存。因此，D是正确答案。
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