Mass Species Extinctions Predicted - Unless...
Mass Species Extinctions Predicted - Unless..
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It doesn’t take a close encounter with a comet to wipe out 40 percent of the
species on earth. Chainsaws and bulldozers can do the job just as well.
Humanity’s destruction of tropical habitat for agriculture, logging and
other development has inflated earth’s normal background extinction rate by
as much as 1,000 times, said Stuart Pimm, a senior research scientist at the
Center for Environmental Research and Conservation.
"This constitutes by far and away our greatest impact on the planet, both
today and for millions of years to come," Pimm said. "Species extinction is
irreversible. Jurassic Park is just a movie."
In an article published in the 24 February issue of Nature entitled
"Extinction by numbers," Pimm and co-author Peter Raven of the Missouri
Botanical Garden examine the potential extinction scenarios for the 21st
Century. The outlook they present is sobering.
Of an estimated 7 million plant and animal species on earth, about 85
percent live on land with about two-thirds of them in the tropics, mostly
the rainforests. Prior to modern human influence, these forests covered
approximately 16 million square kilometers. Today about 8 million remain.
The current rate of forest loss is about 1 million square kilometers every 5
to 10 years and accelerating, with several times that area being damaged by
fires and selective logging.
At this pace, the tropical forests will be gone well before the end of the
century, along with over half of all earth’s species. And on closer
inspection, the picture only gets worse.
It turns out that 30 to 50 percent of all plant, amphibian, reptile, bird
and mammal species are found in just 25 biodiversity "hotspots" that
comprise less than 2 percent of earth’s ice-free land surface. Seventeen of
these hotspots are tropical forest areas where only 12 percent of the
original habitat remains.
Pimm’s analysis indicates that about one-fifth of the species in these 17
areas are either already gone, or on the verge of extinction. Barring
immediate action, within 10 years only those areas already protected from
development will remain, with about 40 percent of the species lost forever.
Luckily the numbers also reveal a ray of hope, if only we heed the warning,
Pimm said.
The relationship between habitat loss and extinction is nonlinear. Initial
destruction of a habitat squeezes most tenant species into shrinking
remnants of their original territory, driving to extinction only those whose
highly restricted ranges are entirely consumed.
Eventually, though, as the remaining habitat shrinks to a small fraction of
its former size, the rate of extinction accelerates rapidly and peaks before
dwindling off as the final surviving species succumb.
While that sounds grim, it also means that the actual extinction impact of
tropical habitat loss thus far has been relatively minor. Although the
rainforests are already half gone, about 85 percent of their species remain.
Thus, strong conservation steps taken now could greatly reduce the tropical
forest extinction rate, which otherwise will peak at nearly 50,000 species
per one million by mid-century, Pimm said.
Moreover, by focusing our immediate conservation efforts on the hotspot
areas at greatest risk, we can achieve an enormous improvement in the
extinction outlook very quickly, even though broad scale conservation will
still be necessary to preserve long-term biodiversity, Pimm said.
The last great global extinction happened about 65 million years ago when
about 40 percent of all the species on earth, including the dinosaurs, were
wiped out. A widely held theory attributes that event to a catastrophic
comet impact, which clogged the atmosphere with dust that blotted out the
sun.
It took about 10 million years for the planet to recover from that loss of
biodiversity, although the assemblage of species, of course, ended up very
different, Pimm said.
"Our actions today, for better or worse, will continue to impact the earth
for millions of years to come," Pimm said. "Unless we take immediate and
efficient steps to curb the rate of tropical habitat loss, particularly in
the hotspot areas, scientists 10 million years hence will view the 21st
Century as we do the end of the Cretaceous -- as a major extinction
catastrophe." - By Kurt Sternlof
Related website
Columbia Earth Institute    http://www.earthinstitute.columbia.edu/

[Contact: Kurt Sternlof]         mailto:[log in to unmask]


28-Feb-2000