At least a third of the world’s frogs, toads and other amphibians are facing extinction because of habitat loss, disease and other threats. Conservationists are racing to save them, but is it too late?

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Conservation

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Six Threats Facing Frogs

Conservation

S eventeen thousand Kihansi spray toads once lived in a lush home under the mist of the Kihansi Gorge waterfalls in Tanzania.

The tiny yellow toads, less than an inch long, were perfectly adapted to the humid jungle where they probably evolved millennia ago. But in 1999, the Tanzanian government rerouted the Kihansi River to build a hydroelectric dam, and the gorge dried up. Without the waterfall’s cooling spray, the toad’s habitat changed and, by 2000, nearly 90 percent of the population had died.

That year, the Wildlife Conserva-tion Society tried to save the species by moving 500 of the remaining toads into breeding programs in zoos in New York and Detroit. In captivity, the toads have both suffered and thrived. At first they fell prey to a parasitic worm, but they bounced back with rapid breeding—so rapid, in fact, that it had to be curtailed in 2002 to prevent the toads from out-growing their habitat. Their population dropped to just 70 individuals in 2004, because of unpredictable breeding and problems with disease.

Back at the gorge, the Tanzanian power authority tried to re-create the waterfall’s mist by installing sprinklers, and after some false starts, the wild-toad population soared back to almost 20,000 in 2003. Later that year, though, a deadly and mysterious skin fungus emerged in the area, decimating the native population once again and ending any hope of reintroducing the captive toads to the wild in the near future. Today, zoos are their only hope.

The Kihansi spray toad is unique—it reproduces by giving birth to fully formed young rather than laying eggs—but its story isn’t. The species found itself in the path of habitat loss and disease, and it could not survive. No spray toads have been spotted in the wild since 2005, and only a few

hundred currently live in captivity. According to the Global Amphibian

Assessment (GAA), a project that tracks the conservation status of the approxi-mately 6,000 known species of amphib-ians, a third of the world’s amphibians are in danger, but the numbers are dif-ficult to confirm and some experts say the true figure could actually be closer to half. In the past three decades, as many as 150 species have disappeared, making this “one of the most wide-spread extinctions to occur since the dinosaurs disappeared 65 million years ago,” says Kevin Zippel, the program director of Amphibian Ark (AArk), an International Union for the Conserva-tion of Nature (IUCN) project.

Why should we protect frogs? To start with, amphibians advance our understanding of biology and evolu-

tion. Just this spring, scientists confirmed the existence of a lung-less frog in the forests in Borneo, revealing a previously

unknown evolutionary

Habitat LossMore than 50 percent of the world’s at-risk amphibians are affected by habitat loss.

Water reclamation is one severe threat to amphibian habitats. The Vegas Valley leop-ard frog died out in the 20th century as the growing city of Las Vegas sucked up streams and springs. The species [drawn here] was last spotted in 1942.

leap. Amphibians also promote medi-cal research. Scientists are working on synthesizing painkillers from poison-dart frogs, for instance, and they hope to study the antibacterial properties of amphibians’ skin for tools to treat hu-man disease. The creatures are also an important part of a larger ecosystem. Amphibians feast on insects and small vertebrates and are, in turn, sustenance for larger animals like birds and fish. From Darwin’s frog in South America, whose males carry tadpoles inside their throats, to the Pignose frog of India, with its purple skin and pointed snout, to Missouri’s one- to two-foot-long Ozark hellbender salamander—all fas-cinating but threatened animals—our planet simply would not be the same place without them.

To protect the future of these and hundreds of other amphibian spe-cies, conservationists have annointed 2008 the Year of the Frog. This ambi-tious campaign spearheaded by AArk includes groups like the World Associa-tion of Zoos and Aquariums and the IUCN. AArk’s mission is to round up the 500 species that cannot be protected in the wild and breed them in the protec-tion of zoos and other centers so that they can one day be reintroduced to the wild. With careful oversight, AArk wants to expand and improve other captive-breeding programs. During the Year of the Frog, the campaign hopes to raise awareness—and $50 million for AArk’s captive-breeding program.

Beyond the Year of the Frog, research is homing in on Batrachochy-trium dendrobatidis, the fungus that factored into the wild Kihansi spray toads’ demise and is wreaking havoc on amphibian populations around the world. Meanwhile, the almost 600

A fungal infection helped to wipe out Costa Rica’s golden toad in just three years.

The golden Kihansi spray toad lost its only habitat when a dam stopped the flow of the Kihansi waterfall in Tanzania. Scientists believe the species now survives only in zoos.

Lethal FungusMany amphibian species infected with the skin fungus Batrachochytrium dendrobatidis developed an infection and then disappeared in record time from the mountain forests of South and Central America in the 1980s and ’90s. In 1987, for instance, biologists counted 1,500 golden toads in Costa Rica’s highlands, but only a single male could be found in 1989, and not one has been spotted since. Chytrid fungus has also been recently linked to amphibian deaths in North America, Europe and Australia, and conservation groups consider it one of the most immediate threats to amphibians.

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PollutionAmphibians exchange water and oxygen through their skin—a trait well-adapted to their wet habitats. But their thin skin also makes them particularly vulnerable to pollution. Chemicals can hamper amphibians’ growth, weaken their immune sys-tem, and cause sexual and develop-mental malformations. Pollution can affect amphibians indirectly as well. Researchers recently confirmed that some fertilizers nurture a snail that hosts a parasitic worm. The worms infect tadpoles living near the snails, causing the tadpoles to form cysts in their developing arms and legs, resulting in deformations such as

missing or extra limbs.

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Conservation

The Pet IndustryPanamanians consider the beautiful golden harlequin frog a good-luck charm, and locals in the central Pana-manian mountains collect the species as pets. The frogs have also been hit with chytrid fungus and habi-tat loss. Thanks to this trifecta, experts say the species will be extinct in the wild within five years. The good news is that tadpoles are being bred in captivity, and may one day be reintroduced to their native habitat.

international scientists who have con-tributed to the GAA so far are creating a comprehensive knowledge base of ever-changing amphibian status. This invaluable information should help reveal new tools to prevent amphibian extinctions.

Homeless Amphibians The GAA’s database is periodically updated with amphibian counts from 12 regions around the world. In the U.S., for instance, there are currently 261 species of amphibians, 52 of which are considered threatened. In Latin America the situation is even worse, with 70 percent of amphibians in danger. By studying patterns in the declining numbers, the GAA is drawing conclusions about the reasons for frogs’ disappearance.

So far, the project has revealed that amphibians everywhere face a complex web of threats [see “Six Threats Facing Frogs,” starting on page 62]. “But habi-tat loss is far and away the single great-est cause of amphibian decline,” says AArk’s Zippel. It affects more than 50 percent of threatened species, according to the GAA, so the IUCN and its Global Amphibian Specialist Group are work-ing to protect diminishing habitats. Last year, the group published the Amphib-ian Conservation Action Plan, which aims to identify the 120 most at-risk habitats and implement conservation

measures for each of them. Amphibians are depen-

dent on moisture, and even

Agricultural runoff allows parasites to infect developing frogs, causing missing and malformed limbs.

have already taken their toll on this newly categorized species. Mer-cury and other residues from illegal gold mining have contaminated the streams where the frog lives. It’s a sad fact: Often, as researchers discover an amphibian species, they find that it’s already going extinct.

Habitat changes can also force species into increasingly smaller areas, limiting how big the population can grow. Mountain-dwelling frogs, for instance, are thought to be adapted to a narrow range of temperatures that exist only at certain altitudes. A warming cli-mate can drive them upward to cooler

environs. The higher the species climb, the less area (and resources) they have at their disposal, resulting in smaller populations. If the warming continues, the species may run out of mountain. According to a new study from the American Museum of Natural History in New York, 30 species of Madagas-car’s mountain-dwelling amphibians and reptiles have moved higher by an average of 62 to 167 feet in response to warming temperatures, reducing the area of their habitat to a precarious level. The study authors predict that at least three of those species could become extinct within the next century.

A Rapid Killer The permeable skin through which most frogs and amphibians breathe is what makes them so sensitive to slight changes in moisture and pollution levels. It also makes them especially vulnerable to toxins and skin diseases. In the past three decades, a vicious fungus has decimated frog populations worldwide. Batrachochytrium dendro-batidis, or amphibian chytrid fungus, causes a disease in which the amphib-ians may lose their outer layer of skin, become frail and sluggish, and eventu-ally die. Scientists still don’t know the fungus’s mechanism and are investi-

AmphibiAn DAnger Zonesthe majority of at-risk species call these 21 nations home, according to the global amphibian assessment. the most widespread threat to amphibians is habitat loss, but diseases like chytrid fungus are the most rapid killers.

Number of threatened species =

Mexico 196

guatemala 76

u.s. 52

cameroon 53 Madagascar 55

cuba 47

ecuador 163 Malaysia 46

china 88costa rica 61

honduras 55

Panama 55

Philippines 48

australia 47Peru 81 sri Lanka 52

colombia 209

india 66

haiti 46

venezuela 69

Brazil 110

a small change in an area’s water can be devastating. “Humans drain swamps, settle around lakes, divert and use streams, and create dams,” says David Bickford, an evolutionary ecologist at the National University of Singapore. “Unfortunately, amphibians happen to live at the freshwater/land interface.” The problem, Bickford says, is particu-larly bad in the heavily populated areas of the tropics—areas like Indonesia, Malaysia, the Philippines, Sri Lanka, India and China.

This spring, he confirmed the existence of the lung-less frog. Man-made changes to its water source

Popular as pets in Panama, golden harle-quin frogs are nearly extinct in the wild.

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in the elevation areas of the harlequin extinctions. That increased cloud cover lowered daytime temperatures in areas that could harbor the fungus, making conditions more ideal for its proliferation. The clouds may also have kept amphibians from sunning themselves—a practice that protects them from chytrid, according to Ross Alford, an ecologist at James Cook University in Australia.

But not everyone agrees that rising tem-peratures equal more fungal infections.

This year, Karen Lips documented how the fungus spreads geographically regardless of climate change, decimat-ing species in waves. “This isn’t an example of a climate-related outbreak,” she says. “It’s just a normal spread of disease.” As for how it’s spreading, she cites frog-to-frog contact, or carriers like birds or bodies of water as possibilities for local transmission of the disease. But she admits they’re just not sure about how it spreads globally.

For now, the jury is out on the precise role of climate, and scientists agree that more research and better data should provide vital clues to the explosion of deadly fungus in the past 30 years. In the meantime, Lips hopes her spreading-wave analysis, which she co-authored with Joseph Mendelson, a herpetologist at Zoo Atlanta, will be useful for identifying species in the path of the fungus. If researchers have information about the direction and rate a disease is spreading—even if they don’t have the answers as to exactly how it’s spreading—they can make predic-tions and take action.

gating whether it works by releasing deadly toxins or by creating a physical barrier that prevents the animal from absorbing oxygen and water.

Disease is an even more immedi-ate threat to amphibians than habitat loss. “I have seen three to five

near extinctions in North America, Eu-rope and Australia—even in places that seemed otherwise safe and pristine.

In addition to its deadly mecha-nism, the fungus presents other myster-ies that make combating it a challenge. Its origin is unknown, but scientists’ best guess at how it spread around the world is the 1930s trade in African clawed frogs. The clawed frogs, which are resistant to the fungus, may have escaped or been released into the wild from labs. In the wild, they may have passed it on to other amphibians. And here chytrid presents another riddle: It’s still unclear how the fungus man-ages to travel around the world.

Scientists are also researching whether chytrid may lie dormant in some areas, becoming active—and deadly—only when an environmental trigger like global warming changes temperature or moisture levels.

In 2006, J. Alan Pounds, a biologist at the Monteverde Cloud Forest Pre-serve in Costa Rica, argued that climate change encouraged the rapid extinc-tion of Central American harlequin frogs by allowing the fungus to thrive. Pounds and other scientists had noticed that that the disappearance of amphib-ians in the 1980s and ’90s coincided with a rapid temperature rise in the tropics—a third of a degree Fahrenheit every decade from 1970 to 2000. At first, a link between increased tempera-ture and a chytrid outbreak seemed paradoxical, because the fungus thrives in a relatively temperate range between 63° and 77°F. Pounds showed, how-ever, that warm years were cloudier

A Captive AudienceFor the 500 amphibian species AArk has deemed unlikely to survive in the wild, that “something” is captive breeding. For now, though, only about 10 percent of those 500 species can be relocated. “Species should be conserved in their native country,” Zippel says. “To do so, captive-breeding programs need to be built in the countries where the most amphibians are threatened.” Before species disappear, AArk hopes to give nations like Colombia and Ecuador (those that are experiencing steep population declines), the capacity to breed their own at-risk animals.

Once in captivity, amphibians are often quarantined and given fungicidal baths to reduce chytrid outbreaks. In the future, better solutions may exist. Recent research from James Madison University suggests that red-backed salamanders, which are resistant to chytrid fungus, may get their resis-tance from a bacteria that lives on their skin. Mountain yellow-legged

frogs coated with the bacteria and then exposed to chytrid fungus lost less weight than untreated frogs—a sign of increased resistance. The researchers posit that it may be possible to pretreat frog populations before the fungus arrives in a particular area. This is why it’s so important to track its spread.

According to Alford, in five to 10 years scientists may be able to use the bacteria to “immunize” captive amphibians against the chytrid fungus. Once released from captivity, those animals will hopefully survive long enough to rebuild the population.

Until then, there is a bright side: The spotted tree frog is proof that captive breeding can work. Australian scientists have bred them since 1998, and a few years ago, they began re-introducing hundreds of the tree frogs back into their former habitat. Today about 150 remain there, and by the end of this year, they should be breed-ing in the wild once again. With any luck, this is just the beginning.

A Single Male Gives an Endangered Species New Lifein 1998, after a frog population once numbering in the thousands had collapsed, aus-tralian biologists rescued the last remaining spotted tree frog in Kosciuszko national Park, in new south Wales. this male was mated with females from a nearby population of spotted tree frogs that was also declining. in 2006, scientists were finally able to re-lease some of their offspring into the wild. Far exceeding expectations, about 150 of them have survived. the group should begin breeding this year.

Invasive SpeciesIn the 1930s, the Central American cane toad was introduced into Australia to devour insects that eat sugar cane crops. The toads proved crummy at pro-tecting sugar cane, but adept at breeding and invading other species’ habi-tats. They had several advantages over native species: They breed and grow quickly, consume a wide variety of resources and, because of their size—up to four pounds—and poisonous skin, they aren’t threatened by predators like the birds and fish that feed on native Australian frogs.

Giant Central American cane toads outcompeted many native frogs in Australia.

fungus-related declines in upland tropi-cal cloud forests, and all populations declined in less than a year,” says Karen Lips, a conservation biologist at South-ern Illinois University who has studied

chytrid fungus in Central America. Other research-

ers have implicated the fungus in the disappearance of two thirds of the 110 colorful species

of Central America’s harlequin frogs over the

past 30 years. It has also contrib-uted to amphibian extinctions and

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Climate ChangeFor mountain-dwelling species adapted to specific altitudes, changing climates can necessitate migration upward, where there’s less space. If the temperatures continue to rise, species may even run out of places to go. Some researchers believe that changing climates in the mountains may also create optimal conditions for the deadly chytrid fungus.

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Conservation

Global warming may have helped the chytrid fungus

wipe out harlequin frogs in Central America.

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