http://www.independent.co.uk/story.jsp?story=2975
05 November 2002 08:21
BDT
Nature 'will take more than 10 million
years' to recover from mankind
By Steve Connor, Science
Editor
09 March 2000
Life on earth will
take at least 10 million years to recover
from the mass extinction of animals and plants brought about
by human activities, say scientists. An investigation of the
ease with which life rebounds after a mass extinction has found
that it takes far longer than previously realised.
Even if man survives
for 2 million years - the average span
for a typical mammal species - the Earth will still be suffering
from his influence millions of years after he has become extinct.
Although there are
now more living species on the planet than
at any other single period in history, they are dying out at
a faster rate than in any of the previous five mass extinctions
over the past 600 million years, the most recent bringing an end
to the dinosaurs 65 million years ago.
Scientists believe
that human activity, ranging from the
destruction of the rainforests to environmental pollution,
is causing a wave of extinctions that is running 10,000 times
faster than would occur naturally.
Two ecologists, James
Kirchner of the University of California,
Berkeley, and Anne Weil of Duke University in North Carolina,
have discovered in their analysis of the five previous mass
extinctions that recovery of species diversity took far longer
than supposed.
"Our results suggest
that there are intrinsic 'speed limits'
that regulate recovery from small extinctions as well as large
ones," they write in the journal Nature.
"Thus, today's
anthropogenic extinctions are likely to have
long-lasting effects, whether or not they are comparable in
scope to the major mass extinctions," they said.
"Even if Homo
sapiens survives several million more years,
it is unlikely that any of our species will see biodiversity
recover from today's extinctions."
Although "background"
extinctions occur all the time, mass
extinctions - where tens of thousands of species are lost
over a relatively short period - are believed to be related
to cataclysmic environmental changes, such as massive volcanic
eruptions or meteor strikes.
The researchers found
that in the immediate aftermath of a
mass extinction there is a serious depletion of the available
ecological niches in which specialist animals and plants can
live. This results in the so-called generalist species - such
as cockroaches and rats - filling the gaps.
Douglas Erwin, a palaeobiologist
at the National Museum of
Natural History in Washington DC, said that during smaller
extinctions niches can be refilled by species closely related
to the ones lost. "But larger extinctions seemingly cause
a
disappearance of the ecological fabric, which can only slowly
be rebuilt," he said.
Only a tiny fraction
of the species that have died out over
the past 500 years - such as the great auk and red macaw -
have actually been recorded as extinct. Meanwhile, thousands
of other animals, ranging from the white rhino and Sumatran
tiger, to the giant tortoise and the golden lion tamarin,
are on the endangered list.
