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次の文章を読み、解答欄の枠内で要旨を述べなさい。（解答欄は100字分のます目）
It seemed obvious. Becasue wolves prey on elk, and elk feed on plants, the wolves' reintroduction to Yellowstone National Park in 1885 should have led to a decline in elk numbers. That would then explain why some plants elk eat are suddenly thriving.
But when Robert Beschta and William Ripple of Oregon State University began to study plant recovery in the park, they found a different twist. "What we're actually seeing is that the size ofthe elk population hasn't changed significantly," Beschta says, "and isn't the biggest factor" in the revival of certain plants -- plants that impact the health of the entire ecosystem from bugs to birds to mammals.
Instead, it seems that fear of predation, not elk numbers, is driving floral recovery -- by changing the ungulates' behavior. Is some areas where wolves now prowl, "elk no longer hang out at the streamside, browsing," Beschta says. "They're more cautious and spend less time where there's a high risk of predation. In those areas, river-loving woody plants like young cottonwoods and willows, once overbrowsed by elk, are taller than they've been in decades. Some are going gangbusters."
This suggests, Beschta says, that the extermination of wolves from the park nearly a century ago -- creating an Eden for wild ungulates -- may have led to the long-term decline of certain plant species. And while wolf reintroduction wasn't done to improve forest health, putting wolves back in the ecosystem may prove key to the survival of riverside plant communities, which in turn strengthen stream banks and provide shade and wildlife habitat.
"How often do you get to connect wolves with warblers?" asked National Park Service biologist Doug Smith, who has headed up the wolf reintroductions. "Here you can: Wolves are, indirectly, helping to bring back nesting habitat for songbirds. As the willows recover, beavers create new aquatic habitats around which life just skyrockets." To regulate the ecosystem and maintain biodiversity, Smith says Yellowstone needs its top dog to keep the elk on their toes.
Beschta agrees. "It's one thing for us to put wolves back into Yellowstone because we took them out," he says. "It's another to put them back becasue the ecosystem requires it." Without wolves in the park today to scare the elk off overbrowsing, "the closk would be running out on remaining cottonwoods," he warns. "They'd eventually disappear. Bringing the wolves back has been an incredible plus."
Further research should tell whether climate and fire history are also affecting floral revival, but some scientists believe they've already found the key -- and not just to the Yellowstone ecosystem. "Wolves seem to have an excessive impact here, and I'm sure the same is true o top predators that have been lost elsewhere," says Beschta. "Perhaps now we can start to appreciate just how important a role these kinds of carnivores play."
</b>Notes</b>
elk: 鹿の一種 predation: cf. predator: an animals that kills and eats other animals ungulate: ひづめのある動物 browse: to eat plants cottonwood: ハコヤナギ aquatic<acqua=water carnivore: an animal that eats flesh
――横浜市立大学 前期日程/医学部 （２月25日実施）――2005年
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- 06/7/3(月) -
