Amphibian decline serves as global warning

The report shows that amphibians are experiencing tens of thousands of years worth of extinctions in the space of a single century, with 122 species having disappeared from the wild since 1980.

The discovery, reported in the journal Science today, is seen by researchers as a potential early warning of impending environmental disaster.

Amphibians act like "natural barometers", because their highly permeable skin makes them so sensitive to the effects of climate change and pollution. Any upheaval in the natural world is likely to affect them first.

More than 500 scientists from 60 nations took part in the Global Amphibian Assessment, the first worldwide audit of their populations.

Over the past three years, the scientists analysed the distribution and conservation status of all 5,743 known amphibian species. Of these, 1,856 - 32 per cent - were threatened with extinction.

Accurate information was lacking on a further 1,300 species which scientists believe may also be under threat.

In comparison, only 12 per cent of bird species and 23 per cent of all mammal species are considered to be endangered.

Russell Mittermeier, the president of Conservation International (CI), which co-led the new research, said: "Amphibians are one of nature’s best indicators of overall environmental health. Their catastrophic decline serves as a warning that we are in a period of significant environmental degradation."

Achim Steiner, director general of the IUCN - World Conservation Union, said: "After birds and mammals, amphibians are the third group of species to be completely evaluated on a global scale. This study significantly expands our knowledge and provides a baseline from which we can monitor our impact on the environment."

He added: "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."

Amphibians were the first terrestrial vertebrates (creatures with a backbone) to colonise the land successfully about 350 million years ago. They have developed a remarkable diversity by adapting to many different aquatic and terrestrial habitats.

Many of the species undergo a classic metamorphosis during their lives, as they develop from aquatic larvae to land-bound adults.

Other species may both metamorphose and spend their entire lives in either aquatic or terrestrial habitats, and in some cases the young may even be born as miniature versions of the adults. Amphibians are present today in every continent except Antarctica, and can be found in almost all habitat types from dry, inhospitable deserts to lush tropical rainforests and temperate climates such as Britain’s.

While a few species are widespread and abundant, many more are found in specialised habitats that are now disappearing fast. The findings show that 43 per cent of all amphibian species are now in decline, with 27 per cent stable. Less than 1 per cent of the population is increasing and the status of the rest remains unknown.

Almost 430 species are on the critically-endangered list, while 761 are listed as endangered and 668 as vulnerable.

Latin America is the worst-affected region in the world for threatened amphibians. Colombia has 208 threatened 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 per cent of its species at risk of extinction.

In the Americas, the Caribbean and Australia, a highly infectious disease called chytridiomycosis has hit amphibians especially hard.

New research shows that in some regions outbreaks of the disease may be linked to years of drought, which scientists are increasingly attributing to climate change.

In most other parts of the world, including Europe, Asia and Africa, chytridiomycosis is much less of a problem, but other threats, such as habitat destruction, air and water pollution and consumer demand, are the leading causes of amphibian decline.

There are 18 species of amphibian recorded in the United Kingdom. Of these, only seven are native. The introduced species have a distribution largely restricted to the areas where they were released.

However, although none of the native or introduced species is considered to be globally under threat by the World Conservation Union (IUCN), four of the native species are under threat within the UK.

The agile frog is now restricted to a single site on the island of Jersey, and the pool frog is possibly already extinct in Britain.

Scotland is the last stronghold of the natterjack toad. Here, this species is at the edge of its global distribution, with a few fragmented populations remaining, including important sites on the Solway Firth. This is Scotland’s most threatened amphibian species.

The crested newt is also found in Scotland, but has seen drastic declines in the rest of the UK.

Scientists believe the world’s amphibians could still be saved by an immediate commitment of reserves and effort. This would mean creating new protected areas.

Captive breeding programmes, better community engagement and protection of freshwater systems would all enhance amphibians’ chances of survival.

Simon Stuart, senior director of the IUCN’s and CI’s Biodiversity Assessment Unit, said: "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 the Earth’s most critical life-support systems is breaking down."

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

Scientists from the IUCN, CI and NatureServe collaborated in the research.