Mass extinction of lizards by 2080

By Emma Young May 14, 2010
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Rising temperatures could drive one fifth of the world’s lizard species extinct within 70 years.

CLIMATE CHANGE HAS ALREADY driven 12 per cent of Mexico’s lizard populations to extinction – and if current warming continues, 20 per cent of lizard species worldwide could go extinct by 2080.

This bleak assessment comes from a major international study led by researchers including David Chapple at Monash University in Melbourne. The work suggests that climate change has already caused local extinctions of two lizard species in Australia and more look set to follow, he says.

“Lizards actually spend a lot of their time trying to keep cool,” says Chapple. “Once it gets too warm for them, they need to retreat into shelter. Obviously if it gets too warm too often, they don’t get enough time to actually be out and about, feeding and looking for mates.”

Too hot to eat

Barry Sinervo at the University of California, Santa Cruz led the work, which is published today in the journal Science. He and his team surveyed 48 species of spiny lizards at 200 sites in Mexico where lizards had been studied between 1975 and 1995. They found that 12 per cent of these local populations had gone.

To test if the climate might be a factor in the extinctions, the team set up temperature-recording devices in lizard-shaped models at various sun-soaked locations in the Yucutan Peninsula. They found that at sites where lizard populations had gone extinct, their model lizards reached temperatures that would have kept real ones largely out of the sun.

The team then developed a model of extinction risk for various species in Mexico, based on air and body temperatures. And they found that the results largely matched the real results.

They then extended the model globally, and – with input from scientists around the world – they found a good match between predicted and actual extinctions. They now predict that, by 2080, 40 per cent of local lizard populations and 20 per cent of species will be gone.

Aussie skinks

In Australia, Chapple found evidence of local extinctions of two species of skink, living in the south of the Northern Territory, and in central Western Australia, which the model had predicted. He hopes to now do a study similar to the one conducted in Mexico.

The model also suggests that live-bearing lizards, which usually live at higher altitudes, are at double the local extinction risk of those that lay eggs.  As temperatures rise, species tend to try to move to stay within their preferred temperature range. “But if you’re an alpine species, and your preferred thermal environment keeps on going up in elevation, there’s only so far you can track it up before you get to the mountain top,” Chapple explains.

South-eastern Australia is well-known for its alpine live-bearing skinks, he adds, and the model suggests they are at risk of extinction, as are other species of skink living in more arid, outback regions.

The work is important partly because it links global warming to actual extinctions, and because there’s a clear biological reason for why hotter temperatures are bad news for lizards. The team “deliver a disturbing message,” writes Richard Huey of the University of Washington, Seattle, and colleagues, in a commentary also published today in Science. “Climate-forced extinctions are not only in the future but are happening now.”

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