ANN. MISSOURI BOT. GARD. 89: 190–198. 2002.
THE DODO WENT EXTINCT
(AND OTHER ECOLOGICAL
MYTHS)
Stuart L. Pimm1
ABSTRACT
The scientific consensus is that human impacts are driving species to extinction hundreds to thousands of times
faster than expected from the natural background rate. Critics challenge this. Perhaps giving them more credit than
they deserve, I examine four concerns. First, that the extinction crisis is not real. It is and high rates of extinction are
the rule, not the exception, within well-known taxa. The second criticism dismisses the problem as one restricted just
to islands. It is not. Island species have special vulnerabilities, but they are far more locally abundant within their
ranges than are continental species with the same range size. There are large numbers of locally rare, continental
species with small geographic ranges that are threatened by human impacts. A third criticism notes the few species
that became extinct following the clearing of forests from eastern North America in the 19th century, casting doubt
upon the relationship between habitat loss and species loss. Analysis of this case history shows that exactly as many
species of birds were lost as expected, for the region had very few species to lose. Extensions to species-rich areas
such as Southeast Asia and the Atlantic coast of Brazil confirm the expected calibrations with an interesting caveat.
Forest losses predict the number of threatened species—those on the verge of extinction—not the number of extinctions.
This leads to the final criticism: that there have been too few recent extinctions. The reply is that in these regions the
deforestation is more recent and species do not go extinct immediately. Some doomed species can linger for decades—
as did the now-extinct species in eastern North America.
Key words: deforestation, extinction, species-area curves.
Among scientists there is a broad consensus that
species are going extinct in unusual numbers. I will
not assemble the evidence for this directly because
there are recent reviews (May et al., 1995; Pimm,
2001; Pimm et al., 1995). Rather, I wish to tackle
the critics who dispute this consensus. Whatever
one thinks of them and those who finance some of
them, however one scorns their willingness to ignore
volumes of inconvenient facts, the critics persist.
They will likely continue to do so while individuals
gain financially from short-term
environmental destruction. Over the last decade, I
have listened to these critics and, perhaps giving
them more credit than they deserve, assembled the
science to rebut them directly. The synthesis I present
here is one based largely on my own work on
birds. This is not because it is unique—far from it;
there is an abundance of evidence to counter these
critics. Rather, it is an attempt to lay out cohesive,
linked arguments into a recipe that readers can
readily apply to other taxa.
There are four criticisms.
1. The extinction crisis is not real. Rather, it is
a ‘‘doomsday myth’’ (Budiansky, 1993). It is the
‘‘facts, not the species’’ that are endangered (Simon
& Wildavsky, 1993: A23), the estimates of extinction
rates are ‘‘strident, inconsistent, and data-free’’
1
Center for Environmental Research and Conservation, MC 5556, Columbia University, 1200 Amsterdam Ave., New
York, New York 100027, U.S.A. StuartPimm@aol.com
(Mann & Plummer, 1995). Since the humid tropical
forests of the Amazon, Congo and New Guinea, and
elsewhere hold the majority of species, their fate is
closely tied to the fate of species. Stott (1999) had
this to say about them: ‘‘‘Tropical rain forest’ does
not exist and never has existed.’’
2. Those who accept that unusual numbers of
extinctions have occurred can still proceed to dismiss
their significance. ‘‘The dodo went extinct’’
proclaims the Oxford English Dictionary. Most recent
extinctions, like the dodo, have been on islands.
The implication is that island species are
wimpy, naı¨ve, and unsophisticated. Perhaps island
species had it coming to them and the urbane, sophisticated
species that populate continents may
not share their fate.
3. Habitat destruction does not cause extinctions—look
at eastern North America, Budiansky
(1993) urged. Projections of future high extinction
rates such as those by Wilson (1988) and Raven
(1988) combine well-documented rates of tropical
forest destruction and a model to predict species
loss from habitat loss. How good are those predictions?
Eastern North America was cleared of its
deciduous forests from 1750 to 1900, yet suffered
few known extinctions. Critics argue that we simply
do not know how to predict the numbers of
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191Pimm
Species Extinction
species that will be lost as tropical forests disap-
pear.
4. In what is mostly a rehashing of earlier myths,
Lomborg (2001) seemed to be asking where are the
bodies to prove an extinction crisis? Some early
efforts did indeed suggest that there should be lots
of extinct species by now. For example, ‘‘one seventh
to one fifth of all species’’ extinct within what
would now have been the last two decades (Barney,
1980: 328). There are not nearly enough, though to
continue the metaphor, there are the requisite number
of seriously wounded ones. So are these species
really dying off at the expected rate—or are our
concerns about them misplaced?
I consider each of these myths in turn.
1. THE EXTINCTION CRISIS IS NOT REAL
Has humanity increased extinction rates beyond
the background rates expected without our impacts?
Those who argue that we have not are claiming
that far too few species have gone extinct in the
recent past. Where should we look for the extinct
species that would reject this assertion?
Pacific islands are the obvious place to start, for
they were the planet’s last habitable areas to be
colonized. Polynesians reached them only within
the last 1000 to 4000 years. The evidence of human
impact is freshest here. (The evidence of humancaused
mass extinctions in Australia, Madagascar,
and the Americas grows more compelling each
year, however (Flannery, 1999)). Pacific island
birds provide unambiguous evidence of massive extinction
(Pimm et al., 1994; Steadman, 1995). The
bones of many bird species persist into, but not
through, archaeological zones showing human pres-
ence.
I will consider the Hawaiian islands in detail.
We know 43 bird species only from their bones. Yet
bird bones are fragile and easily destroyed. We may
never find bones of all the now-extinct species, so
how many are missing? The bone record would be
complete only if all the recent species—those collected
or seen in the last two centuries—were also
found as bones. The proportion of recent species
also found as bones estimates how complete the
sample of species found only as bones is. The proportion
is about a half: across the Hawaiian islands,
we estimate there are about 40 species missing
from the record (Pimm et al., 1994). Add this number
to the 43 known species extinctions and the
body count rises to 83.
James Cook found the Hawaiian islands in 1778.
International trade and colonization followed within
a generation. These new people cleared forests and
introduced cattle and goats. These destroyed native
plants as unprepared for large mammalian herbivores
as the birds were for the rats and pigs the
Polynesians brought with them on their earlier colonization.
Today, our only records of 18 species of
birds are the specimens collected by 19th century
naturalists. The body count rises to 101.
What remains in the Hawaiian islands today?
Pimm et al. (1994) recorded that a dozen species
are so rare that there is little hope of saving them.
If we cannot find these species, then they probably
cannot find each other. A further dozen we can find,
but in numbers so small that their future survival
is uncertain. Of an estimated 136 species, only 11
survive in numbers that suggest a confident future.
Similar extinctions followed across the Pacific.
Over the roughly 1000 years, as the Polynesians
colonized the Pacific from New Zealand, north to
Hawai‘i, and east to Easter Island, they exterminated
ϳ1000 species of birds or ϳ10% of the
world total (Pimm et al., 1994; Curnutt & Pimm,
2001). On some islands, they exterminated all the
bird species they encountered.
They extensively cleared lowland forests, especially
the drier ones (and used only Stone-Age
technology to do so). Birds were not the only victims
of these colonizations, incidentally. Of 980 native
Hawaiian plants, 84 are extinct and 133 have
wild populations of fewer than 100 individuals
(Sohmer, 1994). These plant extinctions were the
consequence of recent human colonizations. Quite
how many plant species the Polynesians exterminated
we may never know.
Few species groups leave traces; land snails are
one and their losses illustrate the bizarre but extensive
devastation that human actions can effect.
A predatory snail, Euglandina rosea, introduced to
many Pacific islands to control another introduced
snail, Achatina fulica, ate to extinction hundreds of
taxa of native Achatinella and Partula land snails
(Hadfield, 1986; WCMC, 1992). (I use the term
‘‘taxa’’ to include recognized geographically distinct
populations. Taxonomic uncertainties often raise
and sink their specific status. For those that are
now extinct we may never resolve the issue.)
Nor are Pacific islands unusual in their species
losses. As European explorers moved from their
coastal waters from the early 1500s, Mauritius, Rodrigues,
and Re´union in the Indian Ocean lost 33
species of birds, including the dodo, 30 species of
land snails, and 11 reptiles. St. Helena and Madeira
in the Atlantic Ocean have lost 36 species of
land snails (WCMC, 1992).
These examples raises two obvious questions.
The first is whether their numbers are unusual or,
192 Annals of the
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alternatively, how many species should we expect
to go extinct each year? The background, that is,
pre-human rates of extinctions fluctuate considerably
over time and surely vary from one species
group to the next. However, a convenient (and likely
conservative) background rate of extinction is
about ‘‘one in a million’’ (May et al., 1995; Pimm
et al., 1995). Only about one in a million species
should terminate their existence naturally within a
year. The bird extinction rate is closer to one bird
species per year from a sample pool of only 10,000
bird species. This means that bird extinctions are
running 100 times the expected rate.
The second obvious question: Do we find evidence
of massive extinctions only on islands?
2. THE DODO WENT EXTINCT (TOO BAD!)
If island species were the only ones at risk, then
we consider their loss to be unfortunate, but relax
in the confidence that they were especially vulnerable.
This argument fails at two levels. The first
failure is that high rates of extinctions occur in
places other than islands. Here are three examples:
(1) A distinct and unusual flora defines the Cape
Floristic Region, which occupies a small area of the
southern tip of Africa. It comprises several vegetational
types of which the fynbos is dominant in
area and contributes the most species. Of the Region’s
9030 species (Goldblatt & Manning, 2002
this issue), 36 species have become extinct in the
last century, and some 618 species are threatened
(Cowling, 1992). (I will always use ‘‘threatened’’ in
a specific, technical sense to mean those species
thought likely to become extinct within at most a
few decades. Quite how long threatened species are
likely to last is a topic I discuss later.)
(2) In North America’s rivers, Williams et al.
(1992) described the mussels and clams in the Mississippi
and St. Lawrence river basins. Of the 297
North American taxa of the two families Unionidae
and Margeritifidae, an estimated 21 have likely
gone extinct since the end of the last century. Another
120 taxa are threatened. Miller et al. (1989)
found that of ϳ950 taxa of freshwater fish in the
United States, Canada, and Mexico, 40 have become
extinct in the last 100 years. Northern lakes,
southern streams, wetlands, and desert springs are
very different habitats, yet all have lost species.
(3) Of the 60 species of recent mammal extinctions
worldwide, 19 are from Caribbean islands
(WCMC, 1992). This repeats the pattern of high
extinction rates of islands, and I will not consider
them further. Interestingly, 18 more were in Australia
(WCMC, 1992), representing ϳ6% of its nonmarine
mammal species. The extinctions have been
equally divided between the southern arid zone—
a sparsely inhabited area of mostly spinifex desert
and extensive pastoralism—and the wheat belt of
the southern tip of Western Australia—where 95%
of the natural woodland has been cleared (Short &
Smith, 1994). Another 43 Australian mammal species
have been lost from more than half of their
former ranges or survive on protected offshore islands
(Burbidge & McKenzie, 1989).
These examples refute the criticism that extinctions
are restricted to islands. In reviewing these
and other examples I am struck by the diversity of
taxa and ecosystems they encompass. Across these
examples, indeed for all well-known taxa, recent
extinction rates are 100 to 1000 times the expected
rate (Pimm et al., 1995; Lawton & May, 1995).
The second failure of the ‘‘it’s just islands’’ criticism
is more surprising. Certainly, greater numbers
and greater fractions of recent species extinctions
have been on islands than on continents. For instance,
since 1600, 97 of the total 108 bird extinctions
have been on islands (Collar et al., 1994).
Island biotas are uniquely vulnerable to the human
introduction of previously absent herbivores, predators,
diseases, and other natural enemies (Pimm,
1991). Species on continents are not so ecologically
naı¨ve.
There is another major factor that determines
threat. Most threatened species have small geographic
ranges (Stattersfield et al., 1998) and island
species’ ranges are inevitably smaller than continental
ones. For a given range size, how do the
island and continental fractions of threatened species
compare?
Manne et al. (1999) calculated the ranges of all
the passerine birds in the Americas and their associated
islands. (They comprise roughly a quarter
of all bird species.) To separate the effects of range
size, and island versus continental distribution, we
calculated the breeding range—henceforth, just
‘‘range.’’ Some of the continental species inhabit
montane habitat ‘‘islands’’ isolated by a ‘‘sea’’ of
lowland habitats. We ask whether these montane
species suffer different levels of threat and so separate
them from lowland species.
Manne et al. showed that for the 14 lowland, 8
montane, and 27 island species with ranges smaller
than 1000 km2
the proportions of threatened species
are high, but uncertain because of the small
sample sizes. Despite these uncertainties, for these
small ranges there is no evidence that island species
are more vulnerable than those on continents.
Perhaps one should expect this. Tiny ranges should
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Species Extinction
make species vulnerable to habitat loss, hunting,
and other threats wherever the species live.
Their most surprising conclusion emerges for
range sizes between 1000 km2
and 100,000 km2
.
Much smaller fractions of montane and island species
are threatened than of lowland species. At
ranges larger than 100,000 km2
the proportions are
uniformly small in all three groups.
This unexpected result at intermediate ranges
has several possible explanations, but we consider
that local abundance is the most likely (Manne &
Pimm, 2001). We find that island species with a
range of (say) 10,000 km2
are often locally abundant
on their island. Montane species with small
ranges are also locally numerous within their ranges.
These examples of numerous species with small
ranges have no match in continental lowlands.
There, species with such small ranges are almost
always very rare within those ranges (Brown, 1984;
Gaston et al., 1997). A reasonable explanation for
the abundance of island species is competitive release
(MacArthur et al., 1972). With fewer competitors,
island species are able to attain higher
densities and are thus less likely to be threatened.
In sum, corrected for range size, continental species
are more—not less—likely to be threatened.
This unexpected vulnerability of continental species
offsets their putative ecological sophistication
and experience of predators and other threats.
There seems to be no reason why continental species
will be spared the high rates of extinction humanity
first vested on insular species.
3. TRASH THE RAINFORESTS JUST AS AMERICANS
DID THEIR FORESTS: NOTHING WILL HAPPEN
Extensive reductions in the forests of eastern
North America occurred during the 19th century.
Surprisingly, only four bird species went extinct:
passenger pigeon, Carolina parakeet, ivory-billed
woodpecker, and Bachman’s warbler from reasons
wholly or mostly from habitat loss. Birds are wellknown,
so we cannot plead ignorance of their extinctions.
Critics use this apparent discrepancy to
claim that fears about massive global extinctions
based on habitat losses are ‘‘simply wrong’’ (Budiansky,
1994). Just how many species should have
gone extinct as a consequence of the loss of forests?
The answer comes from an extension of one of
the most well calibrated ecological relationships
(Rosenzweig, 1995). The function, S ϭ cAz
, frequently
provides a good description of the relationship
between the size of an area, A, and the number
of species, S, that it contains; c and z are constants.
For real islands surrounded by sea, z is usually
about ¼ (Rosenzweig, 1995).
Now, suppose we extend this to forest ‘‘islands’’
that remain amid a ‘‘sea’’ of deforestation. We can
then predict the reduction in numbers of species
from Soriginal to Snow as the habitat’s area is reduced
from Aoriginal—the original extent of forest—to Anow—
the area that now remains as forest ‘‘islands.’’ The
proportion of species lost (Snow/Soriginal) should be
(Anow/Aoriginal)z
. Thus Snow equals Soriginal(Anow/Aoriginal)z
and the number of extinctions, Sextinct equals Soriginal
Ϫ Snow. Notice that we need an estimate of the value
of z, but not of c. Does this recipe work or are one
or more of its assumptions flawed?
In North America, some 48% of the area covered
by the eastern forest at the time of European settlement
(1620) was still wooded at the point of its
lowest forest cover (roughly 1872: Pimm & Askins,
1995). With A1872/A1620 ϭ 0.48 and z ϭ 0.25, we
predict that ϳ17% of the region’s 160 forest birds
(27 species) should have become extinct. It is this
prediction, some six times greater than the four
well-documented extinctions, that causes contro-
versy.
Does this discrepancy cast doubt on the predictions
of species losses from habitat reduction? It
does not. Those who point to the small number of
observed extinctions in the eastern forests mean
global extinctions—species that are lost everywhere.
The prediction of 27 extinctions is based on
the number of species lost only within the region.
Some of these 160 bird species would survive even
if all the eastern forests were cleared. Their distributions
across the boreal forests of Canada or into
Central America would afford them a refuge while
U.S. forests were cleared.
How many species could become globally extinct
if all the eastern forests were felled? Which species
are found only in these forests, that is, how many
species are endemic to them? The answer is only
28. Now 17% of 28 ഠ 4.76. This prediction is
roughly three-quarters of a species higher than the
number of extinctions observed. I will not push my
luck to argue that the endangered red-cockaded
woodpecker, Picoides borealis, is three-quarters of
its way to extinction. The observed and predicted
numbers are remarkably close. This case history is
not the counterexample critics claim it to be. North
America lost few species because it had relatively
few species to lose.
What happens in areas of the world that stand
to lose many species? My colleagues and I have
applied this recipe to two such areas. The first is
insular Southeast Asia (Brooks et al., 1997, 1999a).
The region comprises four archipelagos: the Phil-
194 Annals of the
Missouri Botanical Garden
ippines, the Greater Sundas (Java, Sumatra, and
Borneo), northern Wallacea (Sulawesi and the Moluccas),
and the Lesser Sundas. Their forests hold
585 endemic species of bird—roughly 20 times
that of America’s eastern forest, in half the area.
About 10% of the original area is cleared per decade.
Most of this deforestation has occurred recently
and ϳ60% of the original area is still forested.
Unlike the previous example, deforestation
has not yet caused any confirmed bird extinctions
in insular Southeast Asia. Extinctions take time following
habitat loss, a point to which I must return.
What does the species-area recipe predict about
the details of where extinctions will eventually occur?
Across the region, some areas still have most
of their forests: Borneo had ϳ67%, for example,
when we assembled the forest cover data. (Forests
are shrinking rapidly, however.) Other areas have
almost none: Cebu, in the Philippines has Ͻ 1%.
And some areas have more endemic species than
others. Using the recipe, we predicted the numbers
of threatened bird and mammal species in each of
these four archipelagos, island by island. With a
few, interesting exceptions, there is a statistically
striking correspondence between the numbers of
species we predict should go extinct and those that
are currently threatened. Borneo, for example, has
38 endemics of which only 3 are considered to be
threatened: the recipe predicts 4. Sulawesi and associated
islands also have about two-thirds of their
forest remaining, but there are 146 endemic species
strewn across these islands. The recipe predicts
14 should be threatened with extinction and
16 actually are. In contrast, in the Philippines, the
islands of Mindoro and the western and central Visayas
have 19 endemic species; all are threatened,
while the recipe only predicts that 10 should be.
Where the recipe fails it usually does so by underestimating
the number of threatened species: when
little forest remains, other factors—including hunting
and invasive species—add to the threats.
The second area is the Atlantic coast forest of
Brazil (Brooks & Balmford, 1996). It has 214 endemic
bird species. The area has four major subdivisions
and for each there is a close match between
the numbers of threatened species and those
we predict should become extinct solely on the basis
of habitat loss. (The lowland forests are particularly
hard hit, with only 2% of the forest remaining;
the recipe predicts that 7 of 11 endemic
species should be threatened; 9 are threatened.)
In sum, we have a well-calibrated ecological relationship
that predicts how many species should
become extinct following the loss of habitat across
three continents. Given enough time for the species
to die, as in North America, the predictions are
supported. Worldwide, for every extinct species of
bird there are 10 that are threatened. We predict
these much larger numbers, too, from the loss of
habitat in endemic-rich parts of South America and
tropical Asia. But we are still left with the criticism
that the species have not yet expired. There is a
lingering uncertainty that perhaps our worst fears
will not be realized. That leads to the final criti-
cism.
4. WHERE ARE THE BODIES?
If we are in the midst of an extinction crisis, why
are more species not going extinct? The reply is
that it takes time for (metaphorically) fatally
wounded species to expire. The point is made by
the extinctions of birds in eastern North America.
The low point of forest cover for these forests was
about 1870; the four fatally wounded birds lingered
for several decades, perhaps even a century, before
finally expiring.
This ‘‘many decades’’ matches many other sources
of information. It fits with the IUCN definition
of ‘‘threatened’’—a widely held expert opinion that
threatened species will likely go extinct within a
few decades. And it fits exactly with the few studies
that have explicitly examined forest fragments and
watched how fast species disappear from them
(Brooks et al., 1999b; Pimm & Brooks, 2000).
These studies suggest a species survivorship curve
with a half-life of roughly 50 years. That is, half
the species that will eventually expire do so within
the first 50 years, half of what remain expire in the
next 50 years, and so on. Given these results, over
what time period might the pending massive loss
of species from human actions unfold?
Pimm and Raven (2000) provided several answers.
The first comes from considering the large
fraction of species living within tropical forests and
how fast those forests are shrinking. A second answer
comes from looking at the hotspots—such
places as the Atlantic coast forests of Brazil and
Southeast Asia where endemic species are particularly
concentrated.
About two-thirds of all species occur in the tropics,
most of them in tropical humid forests (Raven,
1980). Such forests include both evergreen rainforests
and more seasonal ones. They originally covered
from 14 to 18 million km2
, depending on the
exact definition, and about half the original area
remains (Skole & Tucker, 1993). Much of the forest
reduction is recent, and clearing now eliminates
about 1 million km2
of tropical forest in 5–10 years.
Burning and selective logging severely damages
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195Pimm
Species Extinction
several times the area that is cleared (Nepstead et
al., 1999; Cochrane et al., 1999).
To convert habitat loss to species loss, one extends
the species-area relationship derived for islands
to predict how many species will not survive
in habitat fragment ‘‘islands’’ that remain amid a
‘‘sea’’ of converted land—as described above. Then
one updates the numbers each year as the total
forested area shrinks. Species that are classified as
threatened will expire in decades to come and they
will be joined by other species for which we are
only now destroying their habitats. The doomed
species do not all die at once, but are spread over
time as determined by the species survivorship
curve. Combining these results gives an extinction
curve that I view as no more than a first sketch that
captures a few salient features.
Because the species-area curve is non-linear, the
clearing to date of half the humid forests should
have fatally wounded 15% of their species. This is
the case. Some 12% of all plants are threatened
(Walter & Gillett, 1998). This estimate is likely to
be an underestimate since many rare species have
yet to be described. Of course, clearing the remaining
half of these forests would eliminate the
other 85% of their species. Thus, the numbers of
fatally wounded species should accelerate rapidly
to a peak by mid century. They will be joined by
ever-larger fractions of species jeopardized by the
interaction between the assumed constant rate of
forest clearing and the non-linear species-area
curve.
The relative height of the peak depends critically
on the fraction of habitat that remains. A value of
5% would protect about 50% of all the forests’ species.
Smaller percentages of remaining forest would
lead to very much smaller estimates of surviving
species. (About 5% of the world’s land surface is
protected at present, but that percentage includes
disproportionately large areas of desert and tundra
ecosystems. Protecting 5% of tropical forests will
require a considerable effort.)
The time delays before extinction mean that
there will be far fewer species going extinct at present
than are being fatally wounded. The model
predicts that current extinction rates should be
modest—on the order of a hundred species per
year, per million species. This matches current estimates
(Pimm et al., 1995). There are as many
bodies as we expect, not far fewer. Extinction numbers
will also peak in mid century, but will be
spread out over a century or more thereafter.
Modest tinkering with parameters does not alter
the ‘‘fewer extinctions now, many more later’’ feature
of this curve, but the contribution of Myers et
al. (2000) does. They show that roughly 30 to 50%
of plant, amphibian, reptile, mammal, and bird species
occur in 25 hotspots that individually are no
more than 2% of the ice-free land surface. These
diverse taxa demonstrate that species with small
ranges are numerous and they are extraordinarily
concentrated. Nature has put her terrestrial species
in relatively few baskets. The sample applies to the
oceans: fishes and other organisms dependent on
coral reefs are similarly concentrated (McAllister et
al., 1994).
Myers et al. (2000) showed that human impacts
are malevolent, not random. Across the 25 hotspots,
an average of 12% of the original primary vegetation
remains. This percentage should be compared
to the roughly 50% for tropical forests as a whole.
Even within the hotspots, Myers et al. found that
the areas richest in endemic plant species have
proportionately the least remaining vegetation and
the smallest areas currently protected (Fig. 1).
A second way to sketch the unfolding extinction
assumes that conservation actions immediately protect
all the remaining habitat areas within the hotspots.
Applying the species-area curve to the individual
hotspots predicts that 18% of all their
species would eventually go extinct. [Since Myers
et al. (2000) showed that hotspots hold 30–50% of
all species, see above, this percentage is also consistent
with the fraction of currently threatened species.]
Yet another sketch assumes that the hotspots’
higher than global average rate of habitat loss continues
for another decade until only the areas currently
protected remain. The hotspots would eventually
lose 44% of all their species (Pimm & Raven,
2000).
None of these three sketches captures the inadequacy
of some of the protected areas, the so-called
‘‘paper parks.’’ Nor do these ideas consider the
added threat of global warming that will doubtless
limit the effectiveness of sharply delimited, small
reserves. Also excluded are the major threats that
invasive species—introduced and weedy species—
pose to the remaining species. Often listed as the
most important factor in causing threat and extinction,
the impacts of invasive species on islands are
well known. Continents are vulnerable, too. Plant
introductions are a major threat to the Cape Region
of South Africa, for instance (Cowling, 1992).
The distinction between these three sketches is
artificial. Many species live in tropical forests that
are also hotspots. Yet others live in tropical forests
that are not and some live in hotspots that are not
tropical forests. Nonetheless, the sketches capture
views of the size and time-scale of the processes
driving the unfolding extinction.
196 Annals of the
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Figure 1. The percentage of the original habitat remaining and the percentage of the original habitat protected are
generally smaller in those hotspots that contain the greatest number of endemic plant species. From data in Myers et
al. (2000).
The first process is the rapidly accelerating loss
of presently extensive, but rapidly shrinking, tropical
forests. Protecting substantial and representative
areas requires prompt action. This is unlikely
to happen unless industrialized nations become
more deeply involved with funding conservation in
developing ones. Without such action, the loss of
species from these areas will overtake the loss of
species from hotspots within a few decades.
The second process is the rate of loss of species
from hotspots. Losses here should dominate for the
next few decades, since hotspots are already severely
fragmented. [By definition: Myers et al.
(2000) defined hotspots to have unusual numbers
of endemic species and to have suffered disproportionate
habitat losses.] Only immediate conservation
actions, including restoration of damaged habitats,
can prevent further species loss. And unless
there is immediate action to salvage the remaining
unprotected areas, the species losses will more than
double. As Myers et al. pointed out, the current
unprotected areas constitute only a little more than
1 million km2
. High concentrations of small-ranged
species make many species vulnerable, but equally
they permit a concerted effort to prevent future ex-
tinctions.
CONCLUSIONS
The dodo did not go extinct. Humanity bludgeoned
it into oblivion. With it went 10% of the
planet’s birds and, in all probability, similar fractions
of other poorly known species of plants and
animals. That we did not identify and name all the
species that disappeared is not a credible argument
for their continued survival. The Vietnam memorial
on the Mall in Washington, D.C., is a poignant list
of all the Americans who died in the U.S.A.’s war
in that country. A far smaller list of names appears
on a memorial in the village in England where I
was born to men who died in France between 1914
to 1918. I recognize those names as just a sample
and, relative to the village’s small population, readily
extrapolate to the massive slaughter of men
across the entire country. While a complete list of
extinct species would be useful, it is not essential
to perceive or to estimate the size of the current
crisis.
Dismissing the threats of future extinctions from
the few that have occurred in North America is
likewise the consequence of misinterpretation. Most
of the recent known bird extinctions on continents
happened in North America following European
Volume 89, Number 2
2002
197Pimm
Species Extinction
colonization. Quite what happened in Europe when
its forests were cleared centuries earlier we may
never know. Consequently, North America is the
crucial case history of forest and species loss. It
teaches that we lost 4 of 28 of its endemic forest
bird species, almost exactly what the species-toarea
calibrations predict on the basis of a 50% reduction
of forests. (Three more species were hunted
to extinction: the great auk, the Labrador duck, and
the Eskimo curlew.) The major tropical forests in
the Amazon, the Congo, and New Guinea have already
lost half their area, are shrinking by the day,
and yet they hold more than 10 times the number
of bird species that were found in eastern North
America. The hotspots are already depleted even
further. The North American case history is most
telling when scaled appropriately.
Some scientists have overestimated the numbers
of species that should be going extinct per year at
present. The fault lies solely with the assumption
that species would die out immediately. Some do,
but most manage to linger. We have yet to realize
the 10% loss of species—roughly the fraction of
well-known species that are threatened—because
the destruction of the most species-rich ecosystems
has only unfolded in the last half century. Yet this
overestimation is simply fixed by changing the text
from predictions of ‘‘actual extinctions’’ to predictions
of species ‘‘being on an inexorable path to
extinction.’’ Unless we protect more of the planet’s
remaining natural areas, by the end of this century
that distinction will seem absurdly trivial.
Literature Cited
Barney, G. O. 1980. The Global 2000 Report to the President,
Vol. 2. U.S. Government Printing Office, Washington,
D.C.
Brooks, T. M. & A. Balmford. 1996. Atlantic Forest extinctions.
Nature 380: 115.
, S. L. Pimm & N. J. Collar. 1997. Deforestation
predicts the number of threatened birds in insular
Southeast Asia. Conservation Biol. 11: 382–384.
, , V. Kapos & C. Ravilious. 1999a. Threat
from deforestation to montane and lowland birds and
mammals in insular Southeast Asia. J. Animal Ecol. 68:
1061–1078.
, & J. O. Oyugi. 1999b. Time lag between
deforestation and bird extinction in tropical forest fragments.
Conservation Biol. 13: 1140–1150.
Brown, J. H. 1984. On the relationship between abundance
and distribution of species. Amer. Naturalist 124:
255–279.
Budiansky, S. 1993. The doomsday myths. U.S. News and
World Report, December 13, 1993, 81–83.
. 1994. Extinction or miscalculation? Nature 370:
104–105.
Burbidge, A. A. & N. L. McKenzie. 1989. Patterns in the
modern decline of Western Australia’s vertebrate fauna:
Causes and conservation implications. Biol. Conservation
50: 143–198.
Cochrane, M. A., A. Alencar, M. D. Schulze, C. M. Souza,
Jr., D. C. Nepstad, P. Lefebvre & E. A. Davidson. 1999.
Positive feedbacks in the fire dynamic of closed canopy
tropical forests. Science 284: 1832–1835.
Collar, N., M. Crosby & A. Stattersfield. 1994. Birds to
Watch 2. Smithsonian Institution Press, Washington,
D.C.
Cowling, R. M. (editor). 1992. The Ecology of Fynbos.
Oxford Univ. Press, Cape Town.
Curnutt, J. & S. L. Pimm. 2001. How many bird species
in Hawai‘i and the Central Pacific before first contact?
Pp. 15–30 in J. M. Scott, S. Conant & C. van Riper III
(editors), Evolution, Ecology, Conservation, and Management
of Hawaiian Birds: A Vanishing Avifauna.
Studies in Avian Biology 22.
Flannery, T. F. 1999. Debating extinction. Science 283:
182–183.
Gaston, K., T. Blackburn & J. Lawton. 1997. Interspecific
abundance-range size relationships: An appraisal of
mechanisms. J. Animal Ecol. 66: 579–601.
Goldblatt, P. & J. C. Manning. 2002. Plant diversity of
the Cape Region of southern Africa. Ann. Missouri Bot.
Gard. 89: 281–302.
Hadfield, M. G. 1986. Extinction in Hawaiian achatinelline
snails. Malacologia 27: 67–81.
Lawton, J. H. & R. M. May 1995. Extinction Rates. Oxford
Univ. Press, Oxford & New York.
Lomborg, B. 2001. The Skeptical Environmentalist: Measuring
the Real State of the World. Cambridge Univ.
Press, Cambridge.
MacArthur, R. H., J. M. Diamond & J. Karr. 1972. Density
compensation in island faunas. Ecology 53: 330–342.
Mann, C. C. & M. L. Plummer. 1995. Noah’s Choice. Alfred
A. Knopf, New York.
Manne, L. L. & S. L. Pimm. 2001. Beyond eight forms of
rarity: Which species are threatened and which will be
next? Animal Conservation 4: 221–230.
, T. M. Brooks & S. L. Pimm. 1999. Relative risk
of extinction of passerine birds on continents and islands.
Nature 399: 258–261.
May, R. M., J. H. Lawton & N. E. Stork. 1995. Assessing
extinction rates. Pp. 1–24 in J. H. Lawton & R. M. May
(editors), Extinction Rates. Oxford Univ. Press, Oxford.
McAllister, D., F. W. Schueler, C. M. Roberts & J. P. Hawkins.
1994. Mapping and GIS analysis of the global
distribution of coral reef fishes on an equal-area grid.
Pp. 155–175 in R. Miller (editor), Advances in Mapping
the Diversity of Nature. Chapman & Hall, London.
Miller, R. R., J. D. Williams & J. E. Williams. 1989.
Extinctions of North American fishes during the past
century. Fisheries 14: 22–38.
Myers, N., R. A. Mittermeier, C. G. Mittermeier, G. A. B.
da Fonseca & J. Kent. 2000. Biodiversity hotspots for
conservation priorities. Nature 403: 853–858.
Nepstead, D. C., A. Verssimo, A. Alencar, C. Nobre, E.
Lima, P. Lefebvre, P. Schlesinger, C. Potter, P. Moutinho,
E. Mendoza, M. Cochrane & V. Brooks. 1999.
Large-scale impoverishment of Amazonian forests by
logging and fires. Nature 398: 505–508.
Pimm, S. L. 1991. The Balance of Nature? Univ. Chicago
Press, Chicago.
. 2001. The World According to Pimm: A Scientist
Audits the Earth. McGraw Hill, New York.
& R. Askins. 1995. Forest losses predict bird ex-
198 Annals of the
Missouri Botanical Garden
tinctions in eastern North America. Proc. Natl. Acad.
Sci. U.S.A. 92: 9343–9347.
& T. M. Brooks. 2000. The Sixth Extinction: How
large, how soon, and where? Pp. 46–62 in P. Raven
(editor), Nature and Human Society: The Quest for a
Sustainable World. National Academy Press, Washington,
D.C.
& P. H. Raven. 2000. Extinction by numbers. Nature
403: 843–845.
, M. P. Moulton & L. J Justice. 1994. Bird extinctions
in the central Pacific. Philos. Trans. Roy. Soc.
London B344: 27–33.
, J. Russell, J. L. Gittleman & T. M Brooks. 1995.
The future of biodiversity. Science 269: 347–350.
Raven, P. H. (editor). 1980. Research Priorities in Tropical
Biology. National Academy of Sciences Press, Washington,
D.C.
. 1988. Our diminishing tropical forests. Pp. 119–
122 in E. O. Wilson & F. M. Peter (editors), Biodiversity.
National Academy Press, Washington, D.C.
Rosenzweig, M. L. 1995. Species Diversity in Space and
Time. Cambridge Univ. Press, Cambridge, U.K.
Short, J. & A. Smith. 1994. Mammal decline and recovery
in Australia. J. Mammalogy 75: 288–297.
Simon, J. L. & A. Wildavsky. 1993. Facts, not species,
are periled. New York Times 142 May 13, 1993: A23.
Skole, D. & C. J. Tucker. 1993. Tropical deforestation and
habitat fragmentation in the Amazon: Satellite data from
1978 to 1988. Science 260: 1905–1910.
Sohmer, S. 1994. Pp. 43–51 in C.-I. Peng & C. H. Chou
(editors), Biodiversity and Terrestrial Ecosystems,
Monograph Series Vol. 14. Institute of Botany, Academia
Sinica, Taipei.
Stattersfield, A. J., M. J. Crosby, A. J. Long & D. C. Wege.
1998. Endemic Bird Areas of the World: Priority Areas
for Biodiversity Conservation. BirdLife Conservation Series
No. 7. Cambridge.
Steadman, D. W. 1995. Prehistoric extinctions of Pacific
Island birds: Biodiversity meets zooarchaeology. Science
267: 1123–1131.
Stott, P. 1999. Tropical Rain Forest: A Political Ecology
of Hegemonic Mythmaking. Studies in the Environment
No. 15, Institute of Economic Affairs, London.
Walter, K. S. & H. J. Gillett. 1998. IUCN Red List of
Threatened Plants. IUCN—The World Conservation
Union, Gland, Switzerland.
WCMC. 1992. Global Biodiversity: Status of the Earth’s
Living Resources. World Conservation Monitoring Centre,
Chapman & Hall, London.
Williams, J. D., M. L. Warren, Jr., K. S. Cummings, J. L.
Harris & R. J. Neves. 1992. Conservation status of
freshwater mussels of the United States and Canada.
Fisheries 18: 6–22.
Wilson, E. O. 1988. Pp. 3–18 in E. O. Wilson & F. M.
Peter (editors), Biodiversity. National Academy Press,
Washington, D.C.