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Thursday, 10 August, 2000, 08:25 GMT 09:25 UK
Vanishing reptiles prompt concern
By environment correspondent Alex Kirby
Scientists say there is evidence that reptiles are undergoing a decline even more marked than that now affecting amphibians.
They say the plight of some populations and species is critical, and that a number face extinction.
Habitat loss and damage are probably the largest single problem, but there are many others.
And so little is known about some reptiles that nobody can be certain whether they are under severe threat.
The alarm is sounded in an article in the journal BioScience, by Dr Whit Gibbons and colleagues. Dr Gibbons, a herpetologist, is professor of ecology at the University of Georgia's Savannah River ecology laboratory.
"There are approximately 7,000 different kinds of reptiles in the world and hundreds of them are recognised as having severe problems, and actually headed towards extinction," Dr Gibbons told the BBC.
Rats, pigs and men
The article says reptiles are declining globally because of six significant threats: habitat loss and degradation, introduced species, pollution, disease, unsustainable use, and climate change.
"Habitat loss and degradation is a major one in virtually every country," Dr Gibbons said. "Reptiles cannot live in a shopping centre and so as we develop we need to do this in a more prudent fashion and consider our wildlife."
He says that even when part of a habitat is protected, such as a wetland, the surrounding area needed by semi-aquatic reptiles may not be.
A prime example of a species at risk from introduced species is the Galapagos tortoise, which the authors say is now close to extinction because of the destruction of its eggs by rats brought on to the islands.
But their decline began when 18th Century sailors used them for food, and it accelerated because of the activities of feral pigs.
Other animals can cause havoc too. The brown tree snake is blamed for steep declines in the numbers of native lizards on 13 of the Marianas islands. Elsewhere, non-native plant species have adversely affected reptile populations.
Pollutants known to harm reptiles include metals, pesticides and herbicides, fertilisers, radioactive waste, and the so-called "gender benders" - endocrine disrupters.
Reptiles are also subject to a range of diseases and parasites, including a widespread upper respiratory tract disease affecting desert tortoises in the US southwest, and shell diseases which have been implicated in turtle declines.
The authors also express concern about the commercial use of reptiles, though they say this is not universally bad.
The problem is that, when they are taken for the pet trade, food, or for traditional medicine, the rate of killing may be unsustainable. Yet some long-lived species take years to reach maturity, and are therefore slow to reproduce.
Eating to extinction
"Most species of sea turtles continue to decline in all warm oceans of the world", write the BioScience authors.
"The estimated worldwide population of leatherbacks nesting on beaches in 1980 was 115,000, compared with just 34,500 in 1995.
"Populations of several boa and python species have declined because of harvesting of wild snakes for their skins."
On climate change, the authors say they "accept the argument that the Earth is undergoing unprecedented rapid climatic change".
They say reptiles are particularly susceptible to its effects, as these animals are less able than other forms of wildlife to move to a more tolerable habitat.
"This is going to effect some of the egg-laying reptiles," Dr Gibbons told the BBC, "particularly the turtles, because the sex of a turtle is determined by the temperature at which the egg is incubating - likewise, alligators and crocodilians. Climate change could effect sex ratios in populations and this in turn could affect the populations in severe and significant ways."
And apart from the main causes of reptile decline, the article says that some have dwindled or even vanished "without any discernible causes." These include the gastric brooding frog of Australia, whose young develop in the mother's stomach.
Dr Gibbons says that, in the absence of long-term monitoring of many reptile species, the best course for conservation is to assume the worst while gathering more data.
"The disappearance of reptiles from the natural world is genuine and should be a matter of concern," he said. "Current evidence suggests that these declines constitute a worldwide crisis."
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