- The mystery of why lemmings suddenly disappear en masse
has finally been solved by scientists who have categorically ruled out
a suicidal leap over a cliff.
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- Naturalists have long been fascinated by the regular
cycle of boom and bust in the lemming population, which has given rise
to the myth that they rush headlong into the sea.
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- A study in the Arctic tundra of eastern Greenland - where
there is not a cliff in sight - has revealed the true story.
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- Scientists from Helsinki University in Finland who have
been studying the local lemming population for 15 years have found that
the regular four-year cycle of lemming numbers is entirely due to the rodent's
four predators.
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- Although ecologists have always known that predators
control lemming numbers, nobody until now has been able to show precisely
how predators cause the regular four-year cycle of boom and bust.
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- Olivier Gilg, an ecologist, said that the mystery of
why the population of lemmings and their rodent cousins, small voles, increased
by 100 or even 1,000 times and then crashed had been studied for almost
a century. "Different schools have argued about this. It has been
a very, very hot issue," said Dr Gilg, whose study with colleagues
Ilkka Hanski and Benoit Sittler is published in the journal Science.
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- The researchers monitored lemmings and their four predators
- stoats, owls, foxes and a bird called the long-tailed skua. They found
that stoats only feed on lemmings, whereas the other three predators feed
on them only when they become sufficiently numerous. But stoats reproduce
more slowly than lemmings, so stoat population growth fails to keep pace
with that of the rodents.
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- The researchers found that the foxes, owls and skuas
kept the lemming population in check until stoat numbers caught up, when
the lemming population was quickly driven into decline. At the low point
in the cycle, the three generalists went off to find other food while the
stoat population had to follow the lemmings down.
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- A computer model of the relationship explained the scientific
observations, which made this one of the rare instances when nature appeared
to obey textbook theory, the scientists said.
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- © 2003 Independent Digital (UK) Ltd
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- http://news.independent.co.uk/world/environment/story.jsp?story=458974
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