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http://story.news.yahoo.com/news?tmpl=story&cid=514&e=7&u=/ap/20040318/ap_on_sc/wildlife_gone

Study: Many Species at Risk of Extinction
By PAUL RECER, AP Science Writer

WASHINGTON – A steep decline in birds, butterflies and native plants
in Britain supports the theory that humans are pushing the natural
world into the Earth’s sixth big extinction event and the future may
see more and more animal species disappearing.

In an effort that sent more than 20,000 volunteers into every corner
of England, Scotland and Wales to survey wildlife and plants,
researchers found that many native populations are in big trouble and
some are gone altogether.

“This is the first time, for instance, that we can answer the
question, ‘Have butterflies declined as badly as birds?'” said Jeremy
A. Thomas, an ecologist with the National Environment Research
Council in Dorchester, England, and the first author of a study
appearing in the journal Science.

A survey of 58 butterfly species found that some had experienced a 71
percent population swoon since similar surveys taken from 1970
through 1982. Some 201 bird species were tracked between 1968 and
1971, and then again from 1988 to 1991, with a population decline of
about 54 percent.

Two surveys of 1,254 native plant species showed a decrease of about
28 percent over 40 years.

Thomas said that other scientists, noting losses of mammals and other
animals, have speculated about the loss of insects, but the British
butterfly study is the first to actually document over decades such a
steep decline.

“Population extinctions were recorded in all the main ecosystems of
Britain,” Thomas and his co-authors wrote. This supports the theory,
they said, that “the biological world is approaching the sixth major
extinction event in its history.”

Thomas said that some past extinctions have killed off more than 90
percent of all life forms and “nobody is suggesting we are at that
point.”

But, he said, “if this goes on for the foreseeable future then within
a short period in geological time we will be getting toward the level
of a major extinction.”

Scott Miller, a biologist with the Smithsonian’s National Museum of
Natural History, said the British study was impressive in its
thoroughness. He said, “They may not be representative of the world
as a whole, but they have the best data.”

The data support the idea that the rise of humans over tens of
thousands of years — along with climate changes — is reshaping the
natural world in ways that aren’t thoroughly understood.

Scientists have identified five extinction events in Earth’s history,
with some so severe that more than 90 percent of all life forms died.
The last and most famous extinction was the Cretaceous-Tertiary event
some 63 million years ago that killed the dinosaurs and allowed the
rise of mammals. It is thought to have been caused by an asteroid
hitting Earth.

“We are in the middle of a sixth extinction event that began about
50,000 years ago” with the expanding role in the world of human
beings, said Paul S. Martin, a zoologist and geochemist at the
University of Arizona in Tucson. “It’s happening, but it’s slower and
it is not clear it will be as severe as some of the others.”

Stuart Pimm, an ecologist at Duke University, said in Science that
the British study results “show that we have likely underestimated
the magnitude of the pending extinctions.”

Miller and Martin both point to the hundreds of species, mostly large
animals and birds, that already are gone, some wiped out directly
through human action.

Martin said the fossil records show that the disappearance of many
animals in Australia, Madagascar and North America started about the
time that humans arrived. Gone from the natural North American
environment, for instance, are mammoths, camels, giant sloths and
saber-toothed tigers.

The causes of the other extinctions are not well understood. The
largest ended the Permian Period some 250 million years ago. All but
about 4 percent of all species disappeared then. There were three
other lesser-known events in the Ordovician (435 million years ago),
the Devonian (357 million years ago) and the Triassic (198 million
years ago) periods.

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