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Last Updated: Tuesday, 27 March 2007, 23:05 GMT 00:05 UK
Toads' Australian march quickens

Giant toad. Image: Frogwatch/Getty

The march of the cane toad across Australia is likely to prove more relentless than previously believed, according to a new study.

Writing in the Royal Society's journal Proceedings B, scientists say the toads will double their current range, and spread along most of Australia's coast.

Cane toads were introduced from Hawaii about 70 years ago and are poisonous to some indigenous wildlife.

The new research suggests they are adapting to warmer conditions.

Currently, the toads occupy about 1.2 million sq km (460,000 sq miles) in the northeast of the country, but that is likely to increase to two million sq km (770,000 sq miles), colonising much of the eastern and western coasts as they spread south.

These areas, the researchers note, constitute "a region where most of the continent's human population and biological diversity are concentrated.

"If the cane toad's advance continues, this prolific and problematic species is likely to cause further harm to Australia's unique wildlife and economy," they write.

Toxic terror

Controlling the further expansion of cane toads in Australia remains a daunting task
Mark Urban and colleagues
Cane toads (Bufo marinus) were introduced to the sugarcane fields of Queensland in 1935 in an attempt to control the cane beetle, an agricultural pest.

Quickly they acquired a taste for other creatures, such as smaller frogs and birds, and began to spread. Their current range extends south of the Queensland capital, Brisbane.

There may be as many as 200 million in the country now.

Tough, hardy and equipped with a poisonous skin, not many predators can kill them. Many, including crocodiles, can die from eating them and the toxins they produce.

Just this week a particularly huge example, a 20cm (8 inch) specimen, nick-named "Toadzilla", was discovered in the Northern Territory.

Beyond the homeland

Previous attempts to predict the likely limits of their march started by estimating the extent of Australian territory where the climate and ecology were similar to conditions where the amphibians had evolved in Central and South America.

Map
But the scientists involved in the new research - headed from Yale University in the US by Mark Urban, and including colleagues from Sydney University in Australia - believe the toads have already adapted to conditions beyond those of their "homeland".

In particular they are able to survive where temperatures rise above 37C.

The team also believes that the creatures have evolved to disperse further and faster. Road-building is also making it easier for them to spread, and they appear to thrive in urban environments.

All of this means, the scientists calculate, that previous research has under-estimated the likely scale of the toads' advance.

If they are right, cane toads will become common in major Australian cities such as Adelaide, Melbourne and Perth, with possibly calamitous effects on wildlife.

Can they be stopped? The researchers are pessimistic: "Controlling the further expansion of cane toads in Australia remains a daunting task," they write.

"Future range expansion could devastate Australia's endemic species."




VIDEO AND AUDIO NEWS
The cane toad shown on Australian TV



SEE ALSO
Dog-sized toad found in Australia
27 Mar 07 |  Asia-Pacific
Australians hunt down toxic toads
18 Mar 06 |  Asia-Pacific
Toxic toads 'threaten disaster'
15 Feb 06 |  Science/Nature
Australia MP targets toxic toads
11 Apr 05 |  Asia-Pacific
Snakes bite back at poison toads
08 Dec 04 |  Science/Nature
Toxic toads threaten north Australia
19 Jan 01 |  Asia-Pacific

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