Amphibians in dramatic decline

Posted: 15 October 2004

The world's amphibian species are under unprecedented assault and are experiencing tens of thousands of years worth of extinctions in just a century, according to a recent comprehensive study.

The critically endangered Black-eyed Leaf Frog, Agalychnis moreletii, Mexico. © Twan Leenders
The critically endangered Black-eyed Leaf Frog, Agalychnis moreletii, Mexico. © Twan Leenders
The critically endangered Black-eyed Leaf Frog, Agalychnis moreletii, Mexico© Twan Leenders
More than 500 scientists from over 60 nations contributed to the Global Amphibian Assessment.

Over the past three years, scientists have analysed the distribution and conservation status of all 5,743 known amphibian species - which include frogs and toads, salamanders, and caecilians. Of these, 1,856 species, or 32 per cent, are now considered threatened with extinction. In addition, scientists say that 1,300 other species which have not been assessed are mostly likely threatened with extinction too.

Sensitive creatures

Amphibians are widely regarded as "canaries in the coal mine," since their highly permeable skin is more immediately sensitive to changes in the environment, including changes to freshwater and air quality.

Amphibians are one of nature's best indicators of overall environmental health," said Russell A. Mittermeier, president of Conservation International (CI). "Their catastrophic decline serves as a warning that we are in a period of significant environmental degradation."

Key findings of the study warn that:

  • At least 1,856 amphibian species are threatened with extinction, representing 32 per cent of all species; whereas, only 12 percent of all bird species and 23 percent of all mammal species are threatened, according to IUCN's Red List of Threatened Species.

  • At least nine amphibian species have become extinct since 1980, which saw the start of dramatic declines. Another 113 species have not been reported from the wild in recent years and are considered to be possibly extinct.

  • 43 per cent of all species are in population decline; fewer than one per cent are increasing. Twenty seven per cent are stable, and the rest are unknown.

  • 427 species are considered Critically Endangered (CR), 761 are Endangered (EN), and 668 are Vulnerable (VU).

  • Colombia has 208 threatened amphibian species - the most in the world - followed by Mexico with 191, Ecuador with 163, Brazil with 110, and China with 86. Haiti has the highest percentage of threatened amphibians, with 92 percent of its species at risk of extinction.
"After birds and mammals, amphibians are the third group of species to be completely evaluated on a global scale. This study significantly expands our current knowledge and provides a baseline from which we can monitor our impact on the environment over time," said Achim Steiner, Director General of IUCN-The World Conservation Union. "The fact that one third of amphibians are in a precipitous decline tells us that we are rapidly moving towards a potentially epidemic number of extinctions."

Disease and drought

Chinai Newt, Echinotriton chinhaiensis, critically endangered, China. Photo: Max Sparreboom
Chinai Newt, Echinotriton chinhaiensis, critically endangered, China. Photo: Max Sparreboom
Chinai Newt, Echinotriton chinhaiensis, critically endangered, China.© Max Sparreboom
In the Americas, the Caribbean and Australia, a highly infectious disease called chytridiomycosis has hit amphibians especially hard. New research is showing that in some regions, outbreaks of the disease may be linked to drought years, which scientists are increasingly attributing to the effects of climate change.

But in most parts of the world - including Europe, Asia and Africa - chytridiomycosis is currently less of a problem. Other threats, such as habitat destruction, air and water pollution and consumer demand are leading causes of amphibian decline.

Still, scientists are confident that an immediate commitment of resources and effort could reverse many of the present negative trends. Creating new protected areas, captive breeding programmes, greater community involvement and protection of freshwater systems would enhance amphibians' chances of survival.

"Since most amphibians depend on freshwater and feel the effects of pollution before many other forms of life, including humans, their rapid decline tells us that one of Earth's most critical life support systems is breaking down," said Simon Stuart, Senior Director of the IUCN/CI Biodiversity Assessment Unit, and leader of this research.

"We already knew amphibians were in trouble, but this assessment removes any doubt about the scale of the problem," said Bruce Young, a zoologist with the conservation group NatureServe. "Now we need greater protection of natural areas and accelerated research on amphibian diseases to stem the extinction tide."

Scientists from CI, IUCN, and NatureServe collaborated on the Global Amphibian Assessment. They analyzed data contributed by more than 500 of the world's leading amphibian specialists, and assessed each species for its level of threat, determined the distribution of each species, and gathered other essential ecological information.

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