Ghosts in Our Midst: Coming to Terms with Amphibian Extinctions
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Feature
Ghosts in Our Midst:
Coming to Terms with
Amphibian Extinctions
SCOTT NORRIS
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A global mass extinction of amphibians is well under way, driven both
by habitat loss and by environmental changes. As amphibian
communities in Central America are being decimated by chytrid
disease, scientists are working to fashion an emergency response.
They are also sending out an urgent warning about what the loss of
these environmentally sensitive species may portend.
D isappearing creatures, they re-
semble us in more ways than not.
Frogs and salamanders are, after all,
frogs, toads, salamanders, newts, and
caecilians will become extinct in the
wild in this century. It doesn’t easily sink
fellow vertebrates with arms and legs, in that this is the prognosis for an entire
hands and feet, fingers and toes. What we vertebrate class, like birds or mammals.
see, when we see a frog, is usually a face: But that, precisely, is the scale of the
paired eyes and nostrils set above a broad problem. In just a few decades since the
jaw and a wide, flat-lipped mouth. Behind first glimmerings of a biodiversity crisis,
its face resides a brain, similar to ours, concern over endangered species has
though the cerebrum is small. We are progressed upward through the tax-
evolutionary brethren, the harlequin frog, onomic hierarchy—genus, family,
the axolotl, and us. Much of our ele- order—to this.
mental architecture is the same, bred Why are these losses occurring, and
deep in the germ layers of a body plan what do they portend? Relatively few
more ancient than flowers. Identical people—a small community of re-
chemicals send the same signals inside searchers and conservationists—have
their bodies and ours, and much of what seriously grappled with these questions.
we know about our own embryonic Much has been written about amphib-
development we have learned by study- Once common in Costa Rica and ian declines, and many people are aware
ing theirs. Panama, the lemur leaf frog, of the issue—to a point. But amphib-
The first vertebrates to set foot on Phyllomedusa lemur, now clings to life ians are creatures most of us encounter
earth, amphibians are now becoming in the wild. A successful captive only rarely, and we tend to believe a
ghostly in our midst. Already at least a breeding program for this species has great distance separates their lives and
third, and perhaps half, are at high risk been established at the Atlanta ours. The troubles of frogs, while sad
of extinction. Such widespread endan- Botanical Garden. Photograph: and perhaps alarming, are their own.
germent makes it virtually certain that Ron Holt, courtesy of the Atlanta We are not so delicate; our skin is not
many hundreds, if not thousands, of Botanical Garden. so thin.
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Feature
Amphibia is something we think we can
live with, shouldn’t we be a little more
concerned for ourselves?
Assessing the threat
To be sure, all major segments of biodi-
versity are threatened. Do amphibians
really warrant special consideration? The
GAA set out to answer that question
by pooling all the available information
on the state of the world’s amphibian
populations. Its finding in 2004 that
one-third of the roughly 6000 known
amphibian species are at high risk of ex-
tinction, by IUCN Red List criteria, came
as a shock to many biologists. By com-
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parison, 12 percent of birds and 23 per-
cent of mammals are comparably at risk.
In the Americas the situation is worse:
Nearly 40 percent of amphibians are
threatened. Among salamanders, which
This unnamed species of Eleutherodactylus is known only from dead individuals compose about a tenth of known am-
collected during a chytrid disease die-off in El Cope, Panama. phibian species, endangerment ap-
The species may now be extinct. Photograph: Forrest Brem. proaches 50 percent. Perhaps most
ominous of all is the GAA finding that at
But amphibian biologists are scared, approach agree it’s no solution if am- least 43 percent of all amphibian species
and not only on behalf of the animals phibians can’t also be protected in the are declining, while less than 1 percent are
whose plight they have been document- wild. New networks and secretariats with increasing.
ing. Many see the crisis as our first real ambitious agendas have been established, The disproportionate threat facing
face-to-face brush with our own ecolog- but largely through the volunteer efforts amphibians is even greater than these
ical mortality. The sense of alarm has of scientists and conservation profes- numbers suggest. The GAA categorized
been growing since the first Global Am- sionals with other jobs and other oblig- nearly a quarter of known amphibian
phibian Assessment (GAA) was com- ations. At some point, said one leading species as “data deficient,” meaning
pleted in 2004. The GAA revealed a researcher,“we’re going to have to stop re- their status could not be assessed.
striking fact: Around the world and in lying on people doing this work in their Among species that were assessed, over
large numbers, amphibians are declining spare time.” 40 percent are endangered, and if the
both where their habitat is being de- Amphibians, meanwhile, continue to true status of the data-deficient species
stroyed and in remote areas that appear disappear. Biologists are calling them the were known, the percentage would be
to our eyes pristine. This is particularly canary in the global coal mine, and higher. “Quite a high number [of data-
true in parts of the Americas and Aus- though the phrase has been worn to deficient species] are from areas where
tralia, where infectious fungal disease has death, it’s worth considering anew. Recall there is very little habitat remaining,”
decimated populations, species, entire that the canary’s purpose is served by says IUCN biologist Neil Cox. “It seems
amphibian faunas. Even in protected ar- two things: a physiology it shares with the more and more likely that a large pro-
eas, for many frogs and salamanders, the miner, and a lower threshold of suscep- portion of those species are endan-
inhabitable world is shrinking to nothing. tibility to the poison. The canary dies; gered.” The GAA estimate also falls
These are indeed fearful discoveries, the miner is warned. This is what the short for another reason: Experts be-
and they have prompted the amphibian herpetologists are trying to tell us. Crea- lieve that up to half of the world’s
research community to collectively de- tures with which we biologically have amphibian species have yet to be dis-
clare a state of emergency. Calls have much in common are dying because the covered. Of the several thousand un-
gone out for an unprecedented global environment can no longer support named species thought to exist, it’s a
response, but so far little new funding them. Many are succumbing to a previ- good bet that most have characteris-
has emerged for mobilizing research and ously unknown disease that strikes mul- tics—such as restricted range and small
conservation much beyond the failing tiple species indiscriminately and can population size—that make them vul-
status quo. Captive breeding is emerging erase entire populations. Imagine a com- nerable. Given the likely status of
as a stopgap measure to ward off ex- parably lethal disease affecting mam- several thousand data-deficient and un-
tinctions, but even proponents of this mals. Even if the loss of half of the class named species, a more realistic estimate
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is that at least half of all amphibians are The most pervasive single danger fac-
now threatened with extinction. ing amphibians is loss of habitat, which
Disappearances are hard to document, can directly bring about the extinction of
and conservationists are wary of prema- narrowly distributed species. But habitat
turely declaring a species extinct; so far, loss cannot account for the widespread
the GAA records only a few hundred “enigmatic” declines observed since the
“official” amphibian extinctions. New 1980s. The discovery of the chytrid fun-
species discoveries, in fact, are outpacing gus in 1998 established that infectious
the losses: Somewhat bizarrely, even as disease is a major factor driving the de-
amphibians decline, their known diver- The current status of the Central clines, at least in the Americas and Aus-
sity is increasing. At the same time, the American salamander Oedipina tralia. But the stage for the emergence
potential for new discoveries grows less collaris is unknown, but nearly half and spread of chytridiomycosis may have
as species never recognized by science of all salamanders are considered been set by other factors. At a minimum,
quietly disappear. Sometimes they are threatened. Salamander diversity is it is likely that international trade in am-
caught in the act of vanishing. Recent highest not in the tropics but in the
phibians—including the widespread use
extensive surveys in Sri Lanka failed to eastern United States, including the
of African clawed frogs for pregnancy
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turn up 19 species represented in mu- Appalachian Mountains. The impact
tests in the 1940s—has contributed to
seum collections from the region. While of chytrid fungus in this region
the disease becoming globally established.
studying the 19th-century collections, remains largely unknown.
Alan Pounds, an ecologist working in
biologists turned up two previously un- Photograph: Karen Lips.
Costa Rica since 1981, has assembled evi-
known species, which were named and dence that climate change may help to
declared extinct simultaneously. The case erful drugs. A compound derived from unleash chytrid’s lethal potential. Last
was not unique. “Three or four times I one species of South American poison year in Nature he reported a strong cor-
have described new species from mu- dart frog, for example, blocks pain 200
relation between the timing of disease-
seum specimens, knowing for a fact the times more effectively than morphine.
related die-offs and periods of broad-
species is already extinct,” says Zoo At- Last year researchers at Vanderbilt Uni-
scale warming. A linkage between
lanta amphibian biologist Joe Mendelson. versity reported strong inhibition of the
chytridiomycosis and global warming is
“Without a doubt, many species have HIV virus by skin peptides of frogs in the
something of a paradox, since the fungus
been lost in Mexico and northern Cen- Americas and Australia. Each amphibian
generally thrives best in cool, moist
tral America that were never even extinction entails the possible loss of a
conditions—which is why it has struck
known.” substance that may be of extraordinary
primarily in upland habitats. Pounds’s
In parts of Panama, Southern Illinois benefit to humans, Rabb notes. “How
hypothesis is that increased cloud cover
University herpetologist Karen Lips has can we ignore that, if we care about our-
witnessed the disappearances firsthand. selves?” associated with periods of warming has
Her ongoing field studies have docu- effectively cooled amphibians’ microscale
mented losses of up to 70 percent of the Complexity and chytrid disease environment by reducing the amount of
amphibian species and 90 percent of the The cause of amphibian declines has direct sunlight. But he stresses that even
individuals to chytrid fungal disease. As been a contentious issue since mysterious if his proposed mechanism is disproved,
amphibians disappear in such numbers, die-offs were first noted in Costa Rica in the observed linkage to climate change
so do the ecological roles and services the 1980s. Initially there was a search for still stands. “Frogs tend to decline when
they perform.“Basically, everything we’ve single-factor explanations: Were declines it gets warm,” Pounds says.
looked at is impacted by loss of am- caused by thinning of the ozone layer? Or Lips, on the other hand, says that while
phibians,” Lips says.“Once the frogs and pesticide contamination? Since then, a temperature variation probably does
tadpoles die off, the stream community broad consensus has emerged that un- affect the severity of the infection, the
changes. Algae grow, nitrogen levels derstanding amphibian declines is some- epidemic wave is spreading every year
change, and all that affects the stream thing more akin to understanding what regardless of climate. “I think climate is
food web. We’ve had some frog-eating causes cancer. In this “biocomplexity” important in the chytrid story, but we
snakes go extinct, and other snakes have paradigm, there are no single, simple ex- are still determining exactly how,” Lips
increased. There are cascading effects up planations but rather chains of causality says.“I don’t think it is necessary to invoke
and down.” and synergy among multiple factors.“It’s climate change to explain the spread of
In addition, says zoologist George more complex than just habitat loss here, the fungus among my cloud forest sites
Rabb, former director of Brookfield Zoo, water pollution there, disease in a third in Central America.” Whatever may un-
“we’re losing the evolutionary patents place,” says biologist Claude Gascon, who derlie its origin, Lips says, chytrid fungus
that these creatures developed over a cochairs the IUCN’s Amphibian Spe- is now acting as a novel pathogen affect-
couple hundred million years.”Amphib- cialist Group. “These threats are acting ing populations with no prior exposure
ian skin secretions are a source of pow- cumulatively.” or resistance.
www.biosciencemag.org April 2007 / Vol. 57 No. 4 • BioScience 313
Feature
ply document amphibian declines and
extinctions without also trying to stop
them.”
The ACAP outlines pressing research
needs related to emerging diseases, cli-
mate change, and environmental contam-
ination, and it calls for continuing
diversity studies with a goal of naming
2500 new species in the next 10 years.Var-
ious long-term conservation actions are
described, beginning with efforts to iden-
tify and protect key locations where habi-
tat loss is a severe threat. The plan also
calls for the formation of regionally based
rapid response teams prepared to react
immediately to disease outbreaks, and a
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network of facilities designed to support
“survival assurance colonies” of captive
amphibians. A fund for implementation
has been established, with a target bud-
get set at $400 million for the first five
The marsupial frog, Gastrotheca cornuta (top left), once ranged from Costa Rica to years.
Ecuador, but now is restricted to a small portion of Panama and possibly Colombia. The turn to captive breeding as a re-
The Panamanian golden frog, Atelopus zeteki (top right), has declined more than sponse of last resort has been driven
80 percent over the past decade and is considered critically endangered by the largely by the situation in Central Amer-
IUCN. Small populations remain in the wild and in a number of captive breeding ica. Last year Mendelson and Ron
facilities. Hemiphractus fasciatus (bottom left) is known from only a few localities Gagliardo, of the Atlanta Botanical Gar-
in Panama, Colombia, and Ecuador. The red-eyed tree frog, Agalychnis callidryas den, received extensive media coverage for
(bottom right), remains a common resident in low-elevation forests of southern their “airlift” of amphibians out of
Mexico and Central America. Photographs: Ron Holt, courtesy of the Atlanta Panama. With permission from the Pana-
Botanical Garden (Gastrotheca cornuta, Agalychnis callidryas), Roberto Brenes manian government, the scientists
(Atelopus zeteki), and Forrest Brem (Hemiphractus fasciatus). brought hundreds of threatened frogs to
the United States in suitcases packed with
Regardless of what environmental syn- prohibitively expensive, and shipping damp moss. The attention they received
ergies may underlie its emergence and of samples may be illegal because of helped raise awareness of the extinction
spread, chytrid disease presents the clear- conservation-minded export restrictions crisis, among both the zoological com-
est and most tangible evidence of an that apply to all biological materials. munity and the general public. Mendel-
agent capable of bringing about multiple son says part of the point was to
amphibian extinctions. Unfortunately, The conservation response demonstrate that an emergency response
little is known about the disease outside The biocomplexity view of amphibian in advance of chytrid’s arrival can save
the few areas where it has been extensively declines suggests that there are no fast species.“The airlift operation hinged on
studied. In most locations where enig- and easy solutions. But, just as many the assumption that Karen Lips’s model
matic amphibian declines have occurred, human afflictions must be addressed was correct,” he says.“As it turned out, it
the involvement and present status of from medical, epidemiological, and en- was 100 percent correct. The fungus
chytrid fungus remain unknown. This vironmental health perspectives simul- arrived on schedule and did exactly what
is a colossal blind spot for scientists study- taneously, understanding and preventing it was expected to do. It decimated the
ing amphibian declines. There are simply amphibian declines may require an anal- amphibians in the El Valle region in 2006.
too few field studies, and far too few lab- ogous range of approaches. This range is Now all the streams in the area are vir-
oratories worldwide can perform the reflected in the Amphibian Conserva- tually frogless.”
molecular PCR (polymerase chain re- tion Action Plan (ACAP) released this Even as frogs from Panama were be-
action) test, which is the best way of spring, backed by a newly formed global coming established in Atlanta, the limits
tracking the disease. Currently, says network of researchers under the IUCN’s of species export were clear.“We wanted
Mendelson, most herpetologists work- Amphibian Specialist Group. The ACAP to show that you can go in, work quickly,
ing in Latin America have no way to get stems directly from the 2005 Amphibian and keep animals alive under triage cir-
their field samples analyzed. Use of pri- Summit, where participants declared cumstances,” Mendelson says.“However,
vate labs in the United States may be that it is “morally irresponsible to sim- it is logistically and financially impracti-
314 BioScience • April 2007 / Vol. 57 No. 4 www.biosciencemag.org
Feature
cal—and diplomatically atrocious—to University biologist Reid Harris has de-
say those rescued amphibians have to be scribed inhibition of the fungus by bac-
exported to the US or Europe.” The al- teria isolated from the skin secretions of
ternative solution has been the con- salamanders. Now his studies are focus-
struction of one of the world’s first on-site ing on the mountain yellow-legged frog.
survival assurance facilities in El Valle. “Northern populations are infected and
The Houston Zoo is leading the project, persisting with the chytrid, while south-
working with biologists in Panama and ern populations decline and perhaps go
the support of numerous other zoos in extinct once it arrives,” Harris says. The
the United States and Canada. northern group has a significantly higher
The facility was still under construc- concentration of the antichytrid bacteria,
tion when chytrid fungus arrived in El perhaps enough to prevent an epidemic
Valle last year, and biologists had no from taking off.
choice but to begin collecting frogs. As a Harris has also done experiments to
temporary measure, several hundred ani- see if protective bacteria applied to am-
mals were quarantined and cared for in phibians’ skin can help them ward off
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two rooms in a local hotel. A lengthy the disease.“So far, we have very prelim-
series of delays caused the hotel stay to inary evidence that application of an
drag on for many months before the first antichytrid species of skin bacteria can
animals were finally able to move into the Some frog species facing likely help salamanders clear infection at a
new facility in February. The entire op- extinction in the wild are being faster rate,” he says. “This offers some
eration was extremely labor-intensive, maintained in facilities such as these, hope.” Perhaps some day, Harris says,
says Houston Zoo’s Bill Konstant, but a at the Atlanta Botanical Garden. Zoos amphibians in survival assurance colonies
dozen high-priority species, and 40 over- and aquariums worldwide are being can be inoculated with protective bacteria
all, were protected.“Unfortunately, this is urged to establish a conservation before being returned to the wild. For
the only strategy that makes any sense breeding program for one or more species that can hang on long enough, it
right now,” Konstant says. “Without ac- amphibian species while researchers is also possible that strong selection
tually removing them from their natural seek solutions to the long-term threats against individuals lacking such a de-
environment, there’s no other way to re- facing them. Photograph: Ron fense will lead to the evolution of chytrid
tain these populations.” Gagliardo/Atlanta Botanical Garden. resistance in wild populations.
The conservation breeding approach
is being advanced by the recently formed “But it will fail for many species because Silence in Darien
Amphibian Ark initiative, a joint effort of they will not thrive in captivity, for many Chytridiomycosis is arguably the worst
amphibian conservationists and zoos and others because there is no longer suit- disease ever recorded among vertebrates
aquariums worldwide. The goal is to de- able habitat for them to be reintroduced in its ability to affect large numbers of
velop a greatly expanded capacity for into.” While biologists must do all they species and drive them to extinction. On
housing and retaining amphibian species can, Halliday says, they should not offer the scale by which we are used to think-
that can no longer make it in the wild. false hope.“We have to accept that a very ing about disease in humans, its impact
How many species can actually be pro- large number of species will go extinct,” is scarcely conceivable. But it is just one
tected in this way, and how and when he says, “no matter what we do.” of a growing family of diseases threaten-
they may ultimately be reintroduced into At best, conservation breeding is a ing wildlife and humans—including
the wild, are looming questions. Tim time-buying strategy, based on the hope SARS, West Nile virus, avian influenza,
Halliday, who until last year headed the that conditions suitable for reestablish- and HIV/AIDS—whose emergence has
IUCN’s Declining Amphibian Popula- ment in nature can some day be achieved. been linked to human-caused environ-
tions Task Force, says the approach has its Not all species are susceptible to chytrid mental change. With the full effects of
limits.“Conservationists are attracted to fungus, and scientists are trying to figure global warming still decades away, we
captive breeding because it’s exciting, out why. In what may prove to be an can probably expect worse.
provides good publicity, and people feel important step toward developing a Lips, who has already seen more am-
they’re ‘doing something,’” Halliday says. response to the disease, James Madison phibian die-offs than anyone, is now
preparing for a new survey expedition
into the Darien region of Panama.“It’s the
For more information, visit these sites:
last island of healthy frog populations in
www.amphibiaweb.org/declines all of Central America, and there’s a good
www.cbsg.org/amphibian.php chance there will be a lot of new species,”
www.waza.org/conservation/campaigns21.php?view=campaigns&id=1 Lips says. It’s also the region that appears
to be next in line for chytrid disease to
www.biosciencemag.org April 2007 / Vol. 57 No. 4 • BioScience 315
Feature
strike. “If we can get a list of what is stinctively, perhaps, we all want to shield “Amphibians are giving us a fire drill,
there,” she says,“we can go to the next step ourselves from such knowledge, but by and we have an opportunity to learn
of trying to keep some alive.” The psychic doing so we render ourselves incapable of from it,” says Mendelson. “If we don’t, it
toll of working under such a mandate, responding. The researchers who have will be a criminal oversight.”
Mendelson acknowledges, “is a heavy truly come to terms with amphibian mass
load.... Doing fieldwork, the usual pre- extinctions are unanimous on one point: Scott Norris (e-mail: snorris@nasw.org)
sumption is you take a few samples and
The crisis is indicative of a wider and is a freelance science writer based in
leave, but the animal populations you
immediate danger to the biosphere and Albuquerque, New Mexico.
are studying remain. You assume the
ecology continues. In Darien, that’s not to ourselves. Amphibians are “telling us
going to happen.” something that other groups are not
That’s what class-level endangerment about the severity of what we have done
really means. Our most ingrained as- to the natural world,” says Rabb. “The
sumptions about the continuity of life as amphibians are singularly indicative of a
doi:10.1641/B570403
we know it are suddenly cast in doubt. In- global catastrophe.” Include this information when citing this material.
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