Farewell to the frog?
Frogs and toads are mysteriously disappearing after having being on earth for about 200 million years. Scientists have put forward reasons for this, but a more sinister suggestion is that these amphibians are an early warning signal- that something has gone seriously wrong with the earth's eco-system.
WHEN 1,400 scientists attended the first World Congress of Herpetology in Canterbury, England, in 1989 to hear technical lectures on reptiles and amphibians, they found they shared a troubling and faintly embarrassing problem. The objects of much of their research, frogs and toads, seemed to be disappearing.
Since then, evidence has poured in from every continent except Africa that vast numbers of these often unlovely yet important creatures are vanishing.
Why? A concerted international effort to document the numbers is now under way, but nobody has yet defined the causes.
Certainly humans bear responsibility for removing huge tracts of the amphibians’ habitats on land and in water, and this depredation is an important contributing reason for the decline.
But a more sinister suggestion intrudes, that frogs and toads are an early warning signal, bearers of a fateful message: something has gone fundamentally wrong with the earth’s eco-system.
Because they live in two worlds, eating both plant and insect life, frogs and toads are exposed to more elements. Frogs, with their smooth, moist skin (as opposed to the generally warty, drier toads), are particularly sensitive to their surroundings.
"They are the medium and the message," says Dr David Wake, professor of integrative biology at the University of California, Berkeley.
"I am a relatively cautious scientist but I am very alarmed and feel very strongly about this decline."
"Frogs are tough survivors but they are also delicate, responsive to the, immediate environment, so they act as a symbol. It is clear, their decline is our fault. There is no doubt about that, and it is very, very serious."
Although evidence so far is empiric, it is overwhelming. In Australia, the number of gastric brooding frogs has declined so drastically in 10 years that it is now presumed extinct.
In Costa Rica the golden toad used to swarm by the thousands. None has been seen at the primary breeding site for two years.
In Europe, there is an inexplicable migration east-wards of fire-bellied toads from France and Germany towards Poland and Bulgaria.
In Britain, the natterjack toad and great crested newt are declining, and Dr Tim Halliday at the Open University is conducting a survey to gauge the severity. So far he has identified the loss of lowland heath and coastal dunes as one cause.
But amphibians are disappearing in unspoilt regions, too. High in the Andes, frogs that have adapted to extreme altitudes are vanishing with dramatic suddenness.
"You’d have frogs crawling all over one year, and the next year, none," says William Duellman of the University of Kansas, who has studied them in Peru.
In western America, 80 per cent of the toad population has gone in 15 years.
The Cascade frog that once lived in 50 ponds in the California Nevada area was spotted in only two last year.
The Wyoming toad suffers so badly from "red-leg" disease encouraged by immune deficiency, that its extinction feared.
This disease, which causes the amphibians’ legs to turn red and puffy, is a clue to an ominous theory about declines.
Some scientists wonder if increased ultra-violet radiation is penetrating the creatures’ skins and causing drastic damage to their immune systems.
The red-leg disease, for instance, is caused by infection from freshwater bacteria that frogs can be normally expected to resist.
Unfortunately, the suspected increase of ultra-violet radiation due to ozone depletion has not been proved sufficiently to link it conclusively to amphibian decline.
Another suspect is acid rain, although this is contradicted by some findings. The most obvious is habitat destruction or contamination, as in the introduction into lakes and streams of game fish such as trout that upset food chains and rob frogs of sustenance.
Yet some herpetologists dismiss the idea of a worldwide decline. They believe the current findings to be only an example of cyclical fluctuation.
But here population records are imprecise and do not go far enough back to offer worthwhile comparisons. Indeed, some species said to be disappearing have been identified so recently that normal population swings have never been tabulated.
But herpetologists such as Wake, who says he is open to many interpretations, believe we cannot wait the 20 years that are required for scientific population studies to be carried out.
He helped to establish the Declining Amphibian Populations Task Force, with headquarters in Oregon and units in Europe and Britain and elsewhere, which will conclude a three-year survey at the end of this year.
Frogs and toads have been on earth for about 200 million years. Their loss would be shattering, and not just because of their contribution to insect-control.
"This is about the destruction of our total environment," Wake insists. — The Guardian
Source : News Straits Times, February 9 1993
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