Amphibian decline 'has many causes'

The amphibian decline is happening worldwide

By environment correspondent Alex Kirby

The decline and even disappearance of frogs, toads, newts and salamanders across the world has no single cause, a US biologist says.

Dr Ashley Mattoon, of the Worldwatch Institute, says the declines "involve microscopic pathogens and global climate change, and fields ranging from forestry economics to wildlife toxicology.

"Understanding them will require a much more interdisciplinary, integrative approach than is typical of conventional research."

Writing in World Watch, the Institute's magazine, Dr Mattoon says a decade of research into the amphibians' plight has produced few definitive answers. Of the pressures that appear to underlie most declines, the single most important is habitat loss.

Sudden disaster

Other pressures identified include pollution, the introduction of non-native species, disease, climate change, and exposure to increased levels of ultra-violet radiation because of ozone loss.

But while some declines have no single identifiable cause, Dr Mattoon says many differ from other cases of biodiversity loss in three significant ways.

Amphibians are useful creatures

"Many of the declines appear to have been very sudden. They may also involve whole assemblages of species, so it's not just a question of one or two animals disappearing from an area, but 10 or 20 of them.

"And many declines are occurring in areas where there is no obvious disturbance of any kind. It has been very difficult to understand why this is happening, and it would have been almost impossible to predict it."

A recent example of the more interdisciplinary approach she urges is an international effort to track a pathogenic fungus that is killing frogs in north and central America and in Australia.

Another example is research which may have identified a role for climate change in the disappearance of a frog fauna from Costa Rica.

Species discovered

Dr Mattoon is worried at the "enormous geographical mismatch in research efforts: more than 80% of the amphibian populations studied to date have been north American and European, but the vast majority of amphibian species thus far identified live in the tropics."

A recent five-year survey in Sri Lanka found more than 200 new species there. "That's more than five times the 38 species that were known to comprise the island's amphibian fauna in 1993," said Dr Mattoon.

More research is urgent

"Since so many tropical amphibians are forest animals, we have to assume that deforestation is taking an enormous toll on them. But there's an urgent need for more field research, particularly in tropical moist forests."

She argues too for research to investigate not simply the causes of decline, but also its implications.

Amphibians occupy pivotal positions in many ecosystems, sometimes controlling insects, or keeping algal growth in check. And many species produce substances of great pharmaceutical potential.

Amphibian challenge

Dr Mattoon argues that trying to conserve individual species cannot succeed. "It's just not realistic to assume that every little frog or salamander is going to be able to attract a constituency that will look out for its best interests", she says.

But a truly sustainable society "manages its affairs in ways that prevent large numbers of species from disappearing - even species like most amphibians that will never have any political pull.

"Amphibian decline is a fundamental challenge to the way we live. We may not understand all the biological particulars, but the ethical issue is now very clear."

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