Cane toads could take over Australia
Cane toads can adapt so well to Australia's climate that these amphibian pests may eventually spread around three-quarters of the country's coastline, biologists predict.
They says that the cane toad, a poisonous species introduced to northeastern Australia 72 years ago to control sugar-cane pests, may be able to move away from its traditional tropical and sub-tropical home and adapt to drier conditions.
So, if the researchers' predictions are correct, the toads could one day breed in large areas of Western Australia, South Australia and western Victoria, and in several pockets along the New South Wales coast.
Bufo marinus is one of the world's most notorious examples of an unwanted, invasive pest, as its relentless spread has devastated populations of toads and frogs, and other native species.
In February 2006, biologists estimated the toad had extended its range to more than a million square kilometres in tropical and sub-tropical Australia.
The same team say the unwanted pest's empire has now expanded to 1.2 million square kilometres in a swathe across Queensland and the Northern Territory.
Confounding those who believed that the species would be limited to hot, humid climes, B. marinus has been found to cope with a wide temperature range and dry conditions, the study says.
It now occupies regions where the minimum monthly temperature falls below 5.0°C and the maximum monthly temperature 37.0°C, and has colonised areas where, by all expectations, it should have died from lack of moisture.
Taking the coast road
This shows it has the capability of living in coastal Western Australia and coastal southern Australia, says the paper.
"We predict that cane toads now have the potential to inhabit over 2 million square kilometres of the continent. This estimate includes three-quarters of Australia's coast, a region where most of the continent's human population and biological diversity are concentrated," it says.
"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."
The authors suggest the toads' expansion is down to evolution, the lack of predators and the fabulous niche they found in Australia's habitat.
"If the continuing acceleration of toad expansion reflects continuing adaptation to a new environment, then even our current forecast may prove conservative," they add.
In the February 2006 study, led by Professor Richard Shine of the University of Sydney, toads with longer legs were found to have an evolutionary advantage of shorter-legged counterparts, enabling them to move quicker into new territory.
The success of longer-legged toads helps explain why, in the 1940s, the creature expanded its range by only 10 kilometres a year, while today it is advancing at more than 50 kilometres annually.
Toads that Shine's team radiotagged could hop up to 1.8 kilometres a night during wet weather, a record for any frog or toad.
The size of a small dog
The study into the cane toad's potential new habitats coincides with reports of the capture of a cane toad the size of a small dog in Darwin.
"It's a monster toad," says Paul Cowdy from FrogWatch, which captured the cane toad earlier this week.
"We've never seen a cane toad this big," he says. "It's a male and normally females are bigger."
It is 20.5 centimetres long and weighs 840 grams, twice the normal weight.