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ON THE TERMINATION OF SPECIES
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Ecologists' warnings of an
ongoing mass extinction are being challenged by skeptics and largely
ignored by politicians. In part that is because it is surprisingly hard to
know the dimensions of the die-off, why it matters and how it can best be
stopped
Among the scientists gathered
here in August at the annual meeting of the Society for Conservation
Biology, the despair was almost palpable. "I'm just glad I'm retiring
soon and won't be around to see everything disappear," said P. Dee
Boersma, former president of the society, during the opening night's
dinner. Other veteran field biologists around the table murmured in sullen
agreement.
At the next morning's
keynote address, Robert M. May, a University of Oxford zoologist who
presides over the Royal Society and until last year served as chief
scientific adviser to the British government, did his best to disabuse any
remaining optimists of their rosy outlook. According to his latest rough
estimate, the extinction rate--the pace at which species vanish-accelerated
during the past 100 years to roughly 1,000 times what it was before humans
showed up. Various lines of argument, he explained, "suggest a
speeding up by a further factor of 10 over the next century or so .... And
that puts us squarely on the breaking edge of the sixth great wave of
extinction in the history of life on Earth."
From there, May's lecture
grew more depressing. Biologists and conservationists alike, he complained,
are afflicted with a "total vertebrate chauvinism." Their bias
toward mammals, birds and fish--when most of the diversity of life lies
elsewhere--undermines scientists' ability to predict reliably the scope and
consequences of biodiversity loss. It also raises troubling questions about
the high-priority "hotspots" that environmental groups are scrambling
to identify and preserve.
"Ultimately we have
to ask ourselves why we care" about the planet's portfolio of species
and its diminishment, May said. "This central question is a political
and social question of values, one in which the voice of conservation
scientists has no particular standing." Unfortunately, he concluded,
of "the three kinds of argument we use to try to persuade politicians
that all this is important... none is totally compelling."
Although May paints a
truly dreadful picture, his is a common view for a field in which
best-sellers carry titles such as Requiem for Nature. But is despair
justified? The Skeptical Environmentalist, the new English translation of a
recent book by Danish statistician Bjørn Lomborg, charges that reports of
the death of biodiversity have been greatly exaggerated. In the face of
such external skepticism, internal uncertainty and public apathy, some
scientists are questioning the conservation movement's overriding emphasis
on preserving rare species and the threatened hotspots in which they are
concentrated. Perhaps, they suggest, we should focus instead on saving
something equally at risk but even more valuable: evolution itself.
May's claim that humans
appear to be causing a cataclysm of extinctions more severe than any since
the one that erased the dinosaurs 65 million years ago may shock those who
haven't followed the biodiversity issue. But it prompted no gasps from the
conservation biologists. They have heard variations of this dire forecast
since at least 1979, when Norman Myers guessed in The Sinking Ark that
40,000 species lose their last member each year and that one million would
be extinct by 2000. In the 1980s Thomas Lovejoy similarly predicted that 15
to 20 percent would die off by 2000; Paul Ehrlich figured half would be
gone by now. "I'm reasonably certain that [the elimination of one
fifth of species] didn't happen," says Kirk O. Winemiller, a fish
biologist at Texas A&M University who just finished a review of the
scientific literature on extinction rates.
More recent projections
factor in a slightly slower demise because some doomed species have hung on
longer than anticipated. Indeed, a few have even returned from the grave,
"It was discovered only this summer that the Bavarian vole,
continental Eurasia's one and only presumed extinct mammal [since 1500], is
in fact still with us," says Ross D. E. MacPhee, curator of mammalogy
at the American Museum of Natural History (AMNH) in New York City.
Still, in the 1999 edition
of his often-quoted book The Diversity of Life, Harvard University
biologist E. O. Wilson cites current estimates that between 1 and 10
percent of species are extinguished every decade, at least 27,000 a year.
Michael J. Novacek, AMNH's provost of science, wrote in a review article
this spring that "figures approaching 30 percent extermination of all
species by the mid-21st century are not unrealistic.' And in a 1998 survey
of biologists, 70 percent said they believed that a mass extinction is in
progress; a third of them expected to lose 20 to 50 percent of the world's
species within 30 years.
"Although these
assertions of massive extinctions of species have been repeated everywhere
you look, they do not equate with the available evidence," Lomborg
argues in The Skeptical Environmentalist. A professor of statistics and
political science at the University of Århus, he alleges that
environmentalists have ignored recent evidence that tropical deforestation
is not taking the toll that was feared. "No well-investigated group of
animals shows a pattern of loss that is consistent with greatly heightened
extinction rates," MacPhee concurs. The best models, Lomborg suggests,
project an extinction rate of 0.15 percent of species per decade, "not
a catastrophe but a problem-one of many that mankind still needs to solve.'
"It's a tough
question to put numbers on," Wilson allows. May agrees but says
"that isn't an argument for not asking the question" of whether a
mass extinction event is upon us.
To answer that question,
we need to know three things: the natural (or "background")
extinction rate, the current rate and whether the pace of extinction is
steady or changing. The first step, Wilson explains, is to work out the
mean life span of a species from the fossil record. "The background
extinction rate is then the inverse of that. If species are born at random
and all live exactly one million years--and it varies, but it's on that
order--then that means one species in a million naturally goes extinct each
year," he says.
In a 1995 article that is
still cited in almost every scientific paper on this subject (even in
Lomborg's book), May used a similar method to compute the background rate.
He relied on estimates that put the mean species life span at five million
to 10 million years, however; he thus came up with a rate that is five to
10 times lower than Wilson's. But according to paleontologist David M. Raup
(then at the University of Chicago), who published some of the figures May
and Wilson relied on, their calculations are seriously flawed by three
false assumptions.
One is that species of
plants, mammals, insects, marine invertebrates and other groups all exist
for about the same time. In fact, the typical survival time appears to vary
among groups by a factor of 10 or more, with mammal species among the least
durable. Second, they assume that all organisms have an equal chance of
making it into the fossil record. But paleontologists estimate that fewer
than 4 percent of all species that ever lived are preserved as fossils.
"And the species we do see are the widespread, very successful
ones," Raup says. "The weak species confined to some hilltop or
island all went extinct before they could be fossilized," adds John Alroy
of the University of California at Santa Barbara.
The third problem is that
May and Wilson use an average life span when they should use a median.
Because "the vast majority of species are short-lived," Raup
says, "the average is distorted by the very few that have very long
life spans." All three oversimplifications underestimate the
background rate--and make the current picture scarier in comparison.
Earlier this year U.C.S.B.
biomathematician Helen M. Regan and several of her colleagues published the
first attempt ever to correct for the strong biases, and uncertainties in
the data. They looked exclusively at mammals, the best-studied group. They
estimated how many of the mammals now living, and how many of those
recently extinguished, would show up as fossils. They also factored in the
uncertainty for each number rather than relying on best guesses. In the end
they concluded that "the current rate of mammalian extinction lies
between 17 and 377 times the background extinction rate." The best
estimate, they wrote, is a 36- to 78-fold increase.
Regan's method is still
imperfect. Comparing the past 400 years with the previous 65 million
unavoidably assumes, she says, "that the current extinction rate will
be sustained over millions of years." Alroy recently came up with a
way to measure the speed of extinctions that doesn't suffer from such
assumptions. Over the past 200 years, he figures, the rate of loss among
mammal species has been some 120 times higher than natural.
Attempts to figure out the
current extinction rate are fraught with even more uncertainties. The
international conservation organization IUCN keeps "Red Lists" of
organisms suspected to be extinct in the wild. But MacPhee complains that
"the IUCN methodology for recognizing extinction is not sufficiently
rigorous to be reliable." He and other extinction experts have formed
the Committee on Recently Extinct Organisms, which combed the Red Lists to
identify those species that were clearly unique and that had not been found
despite a reasonable search. They certified 60 of the 87 mammals listed by
IUCN as extinct but claim that only 33 of the 92 freshwater fish presumed
extinct by IUCN are definitely gone forever.
For every species falsely
presumed absent, however, there may be hundreds or thousands that vanish
unknown to science. "We are uncertain to a factor of 10 about how many
species we share the planet with," May points out. "My guess
would be roughly seven million, but credible guesses range from five to 15
million," excluding microorganisms.
Taxonomists have named
approximately 1.8 million species, but biologists know almost nothing about
most of them, especially the insects, nematodes and crustaceans that
dominate the animal kingdom. Some 40 percent of the 400,000 known beetle
species have each been recorded at just one location--and with no idea of
individual species' range, scientists have no way to confirm its
extinction. Even invertebrates known to be extinct often go unrecorded: when
the passenger pigeon was eliminated in 1914, it took two species of
parasitic lice with it. They still do not appear on IUCN's list.
"It is extremely
difficult to observe an extinction; it's like seeing an airplane
crash," Wilson says. Not that scientists aren't trying. Articles on
the "biotic holocaust," as Myers calls it, usually figure that
the vast majority of extinctions have been in the tropical Americas.
Freshwater fishes are especially vulnerable, with more than a quarter
listed as threatened. "I work in Venezuela, which has substantially
more freshwater fishes than all of North America. After 30 years of work,
we've done a reasonable job of cataloguing fish diversity there,"
observes Winemiller of Texas A&M, "yet we can't point to one
documented case of extinction."
A similar pattern emerges
for other groups of organisms, he claims. "If you are looking for hard
evidence of tens or hundreds or thousands of species disappearing each
year, you aren't going to find it. That could be because the database is
woefully inadequate," he acknowledges. "But one shouldn't dismiss
the possibility that it's not going to be the disaster everyone
fears."
The disaster scenarios are
based on several independent lines of evidence that seem to point to fast
and rising extinction rates. The most widely accepted is the species-area
relation. "Generally speaking, as the area of habitat falls, the
number of species living in it drops proportionally by the third root to the
sixth root," explains Wilson, who first deduced this equation more
than 30 years ago. "A middle value is the fourth root, which means
that when you eliminate 90 percent of the habitat, the number of species
falls by half."
"From that rough
first estimate and the rate of the destruction of the tropical forest,
which is about 1 percent a year," Wilson continues, "we can
predict that about one quarter of 1 percent of species either become
extinct immediately or are doomed to much earlier extinction." From a
pool of roughly 10 million species, we should thus expect about 25,000 to
evaporate annually.
Lomborg challenges that
view on three grounds, however. Species-area relations were worked out by
comparing the number of species on islands and do not necessarily apply to
fragmented habitats on the mainland. "More than half of Costa Rica's
native bird species occur in largely deforested countryside habitats,
together with similar fractions of mammals and butterflies," Stanford
University biologist Gretchen Daily noted recently in Nature. Although they
may not thrive, a large fraction of forest species may survive on farmland
and in woodlots--for how long, no one yet knows.
That would help explain
Lomborg's second observation, which is that in both the eastern U.S. and
Puerto Rico, clearance of more than 98 percent of the primary forests did
not wipe out half of the bird species in them, Four centuries of logging
"resulted in the extinction of only one forest bird" out of 200
in the U.S. and seven out of 60 native Species in Puerto Rico, he asserts.
Such criticisms
misunderstand the species-area theory, according to Stuart L. Pimm of
Columbia University. "Habitat destruction acts like a cookie cutter
stamping out poorly mixed dough," he wrote last year in Nature.
"Species found only within the stamped-out area are themselves stamped
out. Those found more widely are not."
Of the 200 bird types in
the forests of the eastern U.S., Pimm states, all but 28 also lived
elsewhere. Moreover, the forest was cleared gradually, and gradually it
regrew as farmland was abandoned, So even at the low point, around 1872,
woodland covered half the extent of the original forest. The species-area
theory predicts that a 50 percent reduction should knock out 16 percent of
the endemic species: in this case, four birds. And four species did go
extinct. Lomborg discounts one of those four that may have been a
subspecies and two others that perhaps succumbed to unrelated insults.
But even if the
species-area equation holds, Lomborg responds, official statistics suggest
that deforestation has been slowing and is now well below 1 percent a year.
The U.N. Food and Agriculture Organization recently estimatedthat from 1990
to 2000 the world's forest cover dropped at an average annual rate of 0.2
percent (11.5 million hectares felled, minus 2.5 million hectares of new
growth).
Annual forest loss was
around half a percent in most of the tropics, however, and that is where
the great majority of rare and threatened species live. So although
"forecasters may get these figures wrong now and then, perhaps colored
by a desire to sound the alarm, this is just a matter of timescale,"
replies Carlos A. Peres, a Brazilian ecologist at the University of East
Anglia in England.
Ecologists have tried
other means to project future extinction rates. May and his co-workers
watched how vertebrate species moved through the threat categories in
IUCN's database over a four-year period (two years for plants), projected
those very small numbers far into the future and concluded that extinction
rates will rise 12- to 55-fold over the next 300 years. Georgina M. Mace,
director of science at the Zoological Society of London, came to a similar
conclusion by combining models that plot survival odds for a few very well
known species. Entomologist Nigel E. Stork of the Natural History Museum in
London noted that a British bird is 10 times more likely than a British bug
to be endangered. He then extrapolated such ratios to the rest of the world
to predict 100,000 to 500,000 insect extinctions by 2300. Lomborg favors
this latter model, from which he concludes that "the rate for all
animals will remain below 0.208 percent per decade and probably be below 0.7
percent per 50 years."
It takes a heroic act of
courage for any scientist to erect such long and broad projections on such
a thin and lopsided base of data. Especially when, according to May, the
data on endangered species "may tell us more about the vagaries of
sampling efforts, of taxonomists' interests and of data entry than about
the real changes in species' status."
Biologists have some good
theoretical reasons to fear that even if mass extinction hasn't begun yet,
collapse is imminent. At the conference in Hilo, Kevin Higgins of the
University of Oregon presented a computer model that tracks artificial
organisms in a population, simulating their genetic mutation rates,
reproductive behavior and ecological interactions. He found that "in
small populations, mutations tend to be mild enough that natural selection
doesn't filter them out. That dramatically shortens the time to
extinction." So as habitats shrink and populations are wiped out--at a
rate of perhaps 16 million a year, Daily has estimated--"this could be
a time bomb, an extinction event occurring under the surface," Higgins
warns. But proving that that bomb is ticking in the wild will not be easy.
And what will happen to
fig trees, the most widespread plant genus in the tropics, if it loses the
single parasitic wasp variety that pollinates every one of its 900 species?
Or to the 79 percent of canopy-level trees in the Samoan rain forests if
hunters kill off the flying foxes on which they depend? Part of the reason
so many conservationists are so fearful is that they expect the arches of
entire ecosystems to fall once a few "keystone" species are
removed.
Others distrust that
metaphor. Several recent studies seem to show that there is some redundancy
in ecosystems," says Melodie A. McGeoch of the University of Pretoria
in South Africa, although she cautions that what is redundant today may not
be redundant tomorrow. "It really doesn't make sense to think the
majority of species would go down with marginally higher pressures than if
humans weren't on the scene," MacPhee adds. "Evolution should
make them resilient."
If natural selection
doesn't do so, artificial selection might, according to work by Werner
Greuter of the Free University of Berlin, Thomas M. Brooks of Conservation
International and others. Greuter compared the rate of recent plant
extinctions in four ecologically similar regions and discovered that the
longest-settled, most disturbed area--the Mediterranean--had the lowest
rate. Plant extinction rates were higher in California and South Africa,
and they were highest in Western Australia. The solution to this apparent
paradox, they propose, is that species that cannot coexist with human land
use tend to die out soon after agriculture begins. Those that are left are
better equipped to dodge the darts we throw at them. Human-induced
extinctions may thus fall over time.
If true, that has several
implications. Millennia ago our ancestors may have killed off many more
species than we care to think about in Europe, Asia and other long-settled
regions. On the other hand, we may have more time than we fear to prevent
future catastrophes in areas where humans have been part of the ecosystem
for a while--and less time than we hope to avoid them in what little
wilderness remains pristine.
"The question is how
to deal with uncertainty, because there really is no way to make that
uncertainty go away," Winemiller argues. "We think the situation
is extremely serious; we just don't think the species extinction issue is
the peg the conservation movement should hang its hat on. Otherwise, if it
turns out to be wrong, where does that leave us?"
It could leave
conservationists with less of a sense of urgency and with a handful of weak
political and economic arguments. It might also force them to realize that
"many of the species in trouble today are in fact already members of
the doomed, living dead," as David S. Woodruff wrote in the
Proceedings of the National Academy of Sciences this past May. "Triage"
is a dirty word to many environmentalists. "Unless we say no species
loss is acceptable, then we have no line in the sand to defend, and we will
be pushed back and back as losses build," Brooks argued at the Hilo
meeting. But losses are inevitable, Wilson says, until the human population
stops growing.
"I call that the
bottleneck," Wilson elaborates, "because we have to pass through
that scramble for remaining resources in order to get to an era, perhaps
sometime in the 22nd century, of declining population. Our goal is to carry
as much of the biodiversity through as possible." Biologists are
divided, however, on whether the few charismatic species now recognized as
endangered should determine what gets pulled through the bottleneck.
"The argument that
when you protect birds and mammals, the other things come with them just
doesn't stand up to close examination," May says. A smarter goal is
"to try to conserve the greatest amount of evolutionary history."
Far more valuable than a panda or rhino, he suggests, are relic life-forms
such as the tuatara, a large iguana-like reptile that lives only on islets
off the coast of New Zealand. Just two species of tuatara remain from a
group that branched off from the main stem of the reptilian evolutionary
tree so long ago that this couple make up a genus, an order and almost a
subclass all by themselves.
But Woodruff, who is an
ecologist at the University of California at San Diego, invokes an even
broader principle. "Some of us advocate a shift from saving things,
the products of evolution, to saving the underlying process, evolution
itself," he writes. "This process will ultimately provide us with
the most cost-effective solution to the general problem of conserving
nature."
There are still a few
large areas where natural selection alone determines which species succeed
and which fail. "Why not save functioning ecosystems that haven't been
despoiled yet?" Winemiller asks. "Places like the Guyana shield
region of South America contain far more species than some of the so-called
hotspots." To do so would mean purchasing tracts large enough to
accommodate entire ecosystems as they roll north and south in response to
the shifting climate. It would also mean prohibiting all human uses of the
land. It may not be impossible: utterly undeveloped wilderness is
relatively cheap, and the population of potential buyers has recently
exploded.
"It turns out to be a
lot easier to persuade a corporate CEO or a billionaire of the importance
of the issue than it is to convince the American public," Wilson says.
"With a Ted Turner or a Gordon Moore or a Craig McCaw involved, you
can accomplish almost as much as a government of a developed country would
with a fairly generous appropriation."
"Maybe even
more," agrees Richard E. Rice, chief economist for Conservation
International. With money from Moore, McCaw, Turner and other donors, CI
has outcompeted logging companies for forested land in Suriname and Guyana.
In Bolivia, Rice reports, "we conserved an area the size of Rhode
Island for half the price of a house in my neighborhood," and the
Nature Conservancy was able to have a swath of rain forest as big as
Yellowstone National Park set aside for a mere $1.5 million. In late July,
Peru issued to an environmental group the country's first "conservation
concession"--essentially a renewable lease for the right to not
develop the land--for 130,000 hectares of forest. Peru has now opened some
60 million hectares of its public forests to such concessions, Rice says.
And efforts are under way to negotiate similar deals in Guatemala and
Cameroon.
"Even without massive
support in public opinion or really effective government policy in the
U.S., things are turning upward," Wilson says, with a look of cautious
optimism on his face. Perhaps it is a bit early to despair after all.
• Extinction
Rates. Edited by John H. Lawton
and Robert M. May. Oxford University Press, 1995.
• The Currency and
Tempo of Extinction. Helen M.
Regan et al. in the American Naturalist, Vol. 157, No. 1, pages 1-10;
January 2001.
• Encyclopedia of
Biodiversity. Edited by Simon
Asher Levin. Academic Press, 2001.
• The Skeptical
Environmentalist. Bjørn Lomborg.
Cambridge University Press, 2001.
• Eminent ecologists warn that humans are causing a mass
extinction event of a severity not seen since the age of dinosaurs came to
an end 65 million years ago. But paleontologists and statisticians have
called such comparisons into doubt.
• It is hard to know how fast species are disappearing.
Models based on the speed of tropical deforestation or on the growth of
endangered species lists predict rising extinction rates. But biologists'
bias towards plants and vertebrates, which represent a minority of life,
undermine these predictions. Because 90 percent of species do not yet have
names, let alone censuses, they are impossible to verify.
• In the face of uncertainty about the decline of
biodiversity and its economic value, scientists are debating whether rare
species should be the focus of conservation. Perhaps, some suggest, we
should first try to save relatively pristine-and inexpensive-land where
evolution can progress unaffected by human activity.
TIMELINE OF EXTINCTION
marks the five most widespread die-offs in the fossil history of life on
Earth.
With more than 1,100
species suspected to have disappeared in the past 500 years, ecologists
fear a sixth mass extinction event is imminent. The die-offs so far,
however, would probably not signal anything unusual to future
paleontologists looking back at our time.
END ORDOVICIAN DURATION: 10 million years (my) MARINE GENERA OBSERVED EXTINGUISHED: 60% CALCULATED MARINE SPECIES EXTINCT: 85% SUSPECTED CAUSE: Dramatic fluctuations in sea level LATE DEVONIAN DURATION: <3 my MARINE GENERA OBSERVED EXTINGUISHED: 57% CALCULATED MARINE SPECIES EXTINCT: 83% SUSPECTED CAUSES: Impact; global cooling; loss of oxygen in oceans END PERMIAN DURATION: Unknown MARINE GENERA OBSERVED EXTINGUISHED: 82% CALCULATED MARINE SPECIES EXTINCT: 95% SUSPECTED CAUSES: Dramatic fluctuations in climate or sea level; asteroid or comet impacts; severe volcanic activity END TRIASSIC DURATION: 3 to 4 my MARINE GENERA OBSERVED EXTINGUISHED: 53% CALCULATED MARINE SPECIES EXTINCT: 80% SUSPECTED CAUSES: Severe volcanism; global warming END CRETACEOUS DURATION: <1 my MARINE GENERA OBSERVED EXTINGUISHED: 47% CALCULATED MARINE SPECIES EXTINCT: 76% SUSPECTED CAUSES: Impact; severe volcanism SPECIES LAST SEEN, EXTINCTION (Scientific name) LOCATION CAUSES Deepwater ciscoe 1952, Lakes Huron Overfishing, (Coregonus johannae) and Michigan hybridization Pupfish 1988, Ojo de Agua La Loss of food (Cyprinodon ceciliae) Presa, Mexico supply Dobson's fruit bat 1970s, Cebu Islands, Forest destruc- (Dobsonia chapmani) Philippines tion, over- hunting Caribbean monk seal 1950s, Caribbean Sea Overhunting, (Monachus tropicalis) harassment Guam flycatcher 1983, Guam Predation by (Myiagra freycinetl) introduced brown tree snakes Kaua'I'O'o 1987, Island of Disease, rat (Moha braccatus) Kaua'I, Hawaii predation Xerces Blue Butterfly 1941, San Francisco Land (Glaucopsyche xerces) Peninsula conversion Tobias' Caddis Fly 1950s, Rhine River, Industrial and (Hydropsyche tobiasi) Germany urban pollution
• SOURCES: Committee on Recently Extinct Organisms;
Birdlife International; Xerces Society; World Wildlife Fund
SURVIVAL OF THE FITTEST
takes on a new meaning when humans develop a region. Among four
Mediterranean climate regions, those developed more recently have lost
larger fractions of their vascular plant species in modern times. Once the
species least compatible with agriculture are filtered out by
"artificial selection," extinction rates seem to fall.
REGION EXTINCT THREATENED (in order of (per 1,000) (percent) development) Mediterranean 1.3 14.7 South African Cape 3.0 15.2 California 4.0 10.2 Western Australia 6.6 17.5 SOURCE: "Extinctions in Mediterranean Areas." Werner Greuter in Extinction Rates. Edited by J.H. Lawton and R.H. May. Oxford University Press, 1995
DIAGRAM: Millions of years
ago
PHOTO (COLOR): END OF AN
ORANGUTAN fixes our attention and seems to confirm our worst fears about
the decline of biodiversity. But does our focus on charismatic animals blur
a view of the big picture? The ape in this photograph died of natural
causes. And a much greater part of the earth's evolutionary heritage rises
from the banks and sits in the water than lies on the log.
PHOTO (COLOR): Trilobite
PHOTO (COLOR): Placoderm
PHOTO (COLOR): Rugose
coral
PHOTO (COLOR): Phytosaur
teeth
PHOTO (COLOR): Mosasaur
PHOTO (COLOR): WEALTH OF
RAIN FORESTS, this one in Borneo, is largely unmeasured, both in biological
and economic terms.
~~~~~~~~
By W. Wayt Gibbs
W. Wayt Gibbs is senior
writer.
How severe is the extinction crisis? That
depends in large part on how many species there are altogether. The greater
the number, the more species will die out every year from natural causes
and the more new ones will naturally appear. But although the general outlines
of the tree of life are clear, scientists are unsure how many twigs lie at
the end of each branch. When it comes to bacteria, viruses, protists, and
archaea (a whole kingdom of single-celled life-forms discovered just a few
decades ago), microbiologists have only vague notions of how many branches
there are.
Birds, fish, mammals and plants are the
exceptions. Sizing up the global workforce of about 5,000 professional
taxonomists, zoologist Robert M. May of the University of Oxford noted that
about equal numbers study vertebrates, plants and invertebrates. "You
may wish to think this record reflects some judicious appreciation of
what's important," he says. "My view of that is: absolute
garbage. Whether you are interested in how ecosystems evolved, their current
functioning or how they are likely to respond to climate change, you're
going to learn a lot more by looking at soil microorganisms than at
charismatic vertebrates."
For every group except birds, says Peter
Hammond of the National History Museum in London, new species are now being
discovered faster than ever before. thanks to several new international
projects. An All Taxa Biodiversity Inventory under way in Great Smoky
Mountains national park in North Carolina and Tennessee has discovered 115
species-80 percent of them insects or arachnids-in its first 18 months of
work. Last year 40 scientists formed the All Species Project, a society
devoted to the (probably quixotic) goal of cataloguing every living
species, microbes included, within 25 years.
Other projects, such as the Global
Biodiversity Information Facility and Species2000, are building Internet
databases that will codify species records that are now scattered among the
world's museums and universities. If biodiversity is defined in strictly
pragmatic terms as the variety of life-forms we know about, it is growing
prodigiously.
TO A FIRST APPROXIMATION, all multicellular species are insects.
Biologists know the least about the true diversity and ecological
importance of the very groups that are most common.
TOTAL SPECIES (BEST ESTIMATE): 8,750,000
NAMED SPECIES: 1,025,000
TOTAL SPECIES (BEST ESTIMATE): 1,500,000
NAMED SPECIES: 72,000
TOTAL SPECIES (BEST ESTIMATE): 1,000,000
NAMED SPECIES: 4,000
TOTAL SPECIES (BEST ESTIMATE): 400,000
NAMED SPECIES: 40,000
TOTAL SPECIES (BEST ESTIMATE): 400,000
NAMED SPECIES: 25,000
TOTAL SPECIES (BEST ESTIMATE): 400,000
NAMED SPECIES: 1,550
TOTAL SPECIES (BEST ESTIMATE): 320,000
NAMED SPECIES: 270,000
TOTAL SPECIES (BEST ESTIMATE): 250,000
NAMED SPECIES: 110,000
TOTAL SPECIES (BEST ESTIMATE): 200,000
NAMED SPECIES: 70,000
TOTAL SPECIES (BEST ESTIMATE): 200,000
NAMED SPECIES: 40,000
TOTAL SPECIES (BEST ESTIMATE): 150,000
NAMED SPECIES: 43,000
TOTAL SPECIES (BEST ESTIMATE): 35,000
NAMED SPECIES: 26,959
TOTAL SPECIES (BEST ESTIMATE): 9,881
NAMED SPECIES: 9,700
TOTAL SPECIES (BEST ESTIMATE): 7,828
NAMED SPECIES: 7,150
TOTAL SPECIES (BEST ESTIMATE): 4,809
NAMED SPECIES: 4,650
TOTAL SPECIES (BEST ESTIMATE): 4,780
NAMED SPECIES: 4,780
• SOURCES: Encyclopedia of Biodiversity,
edited by S.A. Levin; "Biodiversity Hotspots for Conservation
Priorities," by N. Myers et al. in Nature, Vol. 403, pages 853-858;
February 24, 2000; William Eschemeyer (fish species); Marc Van Regenmortel
(virus species); IUCN Red List 2000
PHOTO (COLOR): PYRAMID OF DIVERSITY
PHOTO (COLOR): INSECTS
PHOTO (COLOR): FUNGI
PHOTO (COLOR): BACTERIA AND ARCHAEA
PHOTO (COLOR): ALGAE
PHOTO (COLOR): NEMATODES AND WORMS
PHOTO (COLOR): VIRUSES
PHOTO (COLOR): PLANTS
PHOTO (COLOR): OTHER LIFE
PHOTO (COLOR): MOLLUSKS
PHOTO (COLOR): PROTOZOA
PHOTO (COLOR): CRUSTACEANS
PHOTO (COLOR): FISH
PHOTO (COLOR): BIRDS
PHOTO (COLOR): REPTILES
PHOTO (COLOR): MAMMALS
PHOTO (COLOR): AMPHIBIANS
PHOTO (COLOR)
FOZ DO IGUAÇU, BRAZIL-At the International
Congress of Entomologists last summer, Ebbe Nielsen, director of the
Australian National insect Collection in Canberra, reflected on the reasons
why, despite the 1992 Convention of Biological Diversity signed here in
Brazil by 178 countries, so little has happened since to secure the world's
threatened species. "You and I can say extinction rates are too high
and we have to stop it, but to convince the politicians we have to have
convincing reasons." he said. "In developing countries, the
economic pressures are so high, people use whatever they can find today to
survive until tomorrow. As long as that's the case, there will be no
support for biodiversity at all."
Not, that is, unless it can be made more
profitable to leave a forests standing or a wetland wet than it is to
convert the land to farm, pasture or parking lot. Unfortunately, time has
not been kind to the several arguments environmentalists have made to
assign economic value to each one of perhaps 10 million species.
"Narrowly utilitarian arguments say: The incredible genetic
diversity contained in the population and species diversity that we are
heirs to is ultimately the raw stuff of tomorrow's biotechnological
revolution," observes Robert May of Oxford. "It is the source of
new drugs." Or new foods, adds E.O. Wilson of Harvard, should
something happen to the 30 crops that supply 90 percent of the calories to
the human diet, or to the 14 animal species that make up 90 percent of our
livestock.
"Some people who say that may even believe it," May
continues. "I don't. Give us 20 or 30 years and we will design new
drugs from the molecule up, as we are already beginning to do."
Hopes were raised 10 years ago by reports that Merck had paid $1.14
million in InBio, a Costa Rican conservation group, for novel chemicals
extracted from rain-forest species. The contract would return royalties to
InBio if any of the leads became drugs. But none have, and Merck terminated
the agreement in 1999. Shaman Pharmaceuticals, founded in 1989 to
commercialize traditional medicinal plants, got as far as late-stage
clinical trials but then went bankrupt. And given, as Wilson himself notes
in The Diversity of Life, that more than 90 percent of the known varieties
of the basic food plants are on deposit in seed banks, national parks are
hardly the cheapest form of insurance against crop failures.
"Potentially the strongest argument," May says, "is a
broadly utilitarian one: ecological systems deliver services we're only
just beginning to think of trying to estimate. We do not understand how
much you can simplify these systems and yet still have them function. As
Aldo Leopold once said, the first rule of intelligent tinkering is to keep
all the pieces." The trouble with this argument, explains Columbia
University economist Geoffrey Heal, is that "it does not make sense to
ask about the value of replacing a life-support system." Economics can
only assign the value to things for which there are markets, he says. If
all oil were to vanish, for example, we could switch to alternative fuels
that cost $50 a barrel. But that does not determine the price of oil.
And although recent experiments suggest that removing a large
fraction of species from a small area lowers its biomass and ability to
soak up carbon dioxide, scientists cannot say yet whether the principle
applies to whole ecosystems. "It may be that a grievously simplified
world-the world of the cult movie Blade Runner-can be so run that we can
survive in it," May concedes.
Because science knows so little of the millions of species out
there, let alone what complex roles each one plays in the ecosystems it
inhabits, it may never be possible for economics to come to the aid of
endangered species. A moral argument may thus be the best last
hope-certainly it is appeals to leaders' sense of stewardship that have
accomplished the most so far. But is it hazardous for scientists to make
it?
They do, of course, in various forms. To Wilson, "a species is
a masterpiece of evolution, a million-year-old entity encoded by five
billion genetic letters, exquisitely adapted to the niche it
inhabits." For that reason, conservation biologist David Ehrenfeld
proposed in The Arrogance of Humanism, "long-standing existence in
Nature is deemed to carry with it the unimpeachable right to continued
existence."
Winning public recognition of such a right will take much education
and persuasion. According to a poll last year, fewer than one quarter of
Americans recognized the term "biological diversity." Three
quarters expressed concern about species and habitat loss, but that is down
from 87 percent in 1996. And May observes that the concept of biodiversity
stewardship "is a developed-world luxury. If we were in abject poverty
trying to put food in the mouth of the fifth child, the argument would have
less resonance."
But if scientists "proselytize on behalf of
biodiversity"-as Wilson, Lovejoy, Ehrlich and many others have
done-they should realize that "such work carries perils," advises
David Takacs of California State University at Monterey Bay. "advocacy
threatens to undermine the perception of value neutrality and objectivity
that leads laypersons to listen to scientists in the first place." And
yet if those who know rare species best and love them most cannot speak
openly on their behalf, who will?
PHOTO (COLOR)
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