KEY POINTS:
Is the dingo the potential saviour of Australia's endangered mammals? The maligned wild dog, descended from European wolves, may emerge from two centuries of persecution as the best hope of keeping some of the continent's unique wildlife from extinction.
The case made by James Cook University biologist professor
Chris Johnson is almost heresy in a country that has tried its best to exterminate the dingo since sheep first began to turn the world's driest inhabited continent into one of the planet's most successful and robust economies.
But in a compelling theory, Johnson argues that dingoes should be left alone to roam rural and Outback Australia and should also be re-introduced into vast tracts of land from which they have been exiled by gun and bounty.
Johnson makes his case in a study of the disturbing disappearance of Australian mammals, accelerating alarmingly with the arrival of European settlers.
In Australia's Mammal Extinctions: a 50,000 year history, he says the dog may be the most potent force for reversing one of the world's worst loss of mammal species.
Half of all the mammals that have disappeared in the past two centuries have vanished from Australia. It has been a long and painful process, following two earlier waves that extinguished at least 67 of the 340 species that thrived on the continent 100,000 years ago.
No other continent has suffered so badly. South America lost 10 per cent of the exotic mammals that roamed its forests and plains in the late Pleistocene period. Australia lost 18 per cent.
Johnson says there was no parallel to the later loss of large Australian carnivores, and no South American mammals have become extinct since the arrival of Europeans.
Man has played a key role in the process. There is mounting evidence the impact of humans on huge wombats, marsupial lions and birds three times the size of emus was much greater than earlier believed, with even the relatively small number of Aboriginal hunters adding an intolerable burden to species fighting drought and fire.
"The arrival of people caused two huge environmental changes in Australia," Johnson argues. "First, the extinction of the megafauna [giant mammal species] and then, very probably, rearrangement of the vegetation in consequence of that extinction. Australian environments were transformed within a few thousand years."
The process raced beyond the ability of many species to survive when Europeans arrived. They not only hunted, they caused huge environmental change by farming the continent and introducing such devastating newcomers as foxes, cats and sheep.
Genetic studies suggest dingoes may be descended from a tiny accident - possibly the survival of a single pregnant female from one of the canoes that carried the ancestors of Pacific Islanders from Asia.
Johnson says they took dogs with them, possibly for food: "Some of these travelling dogs may have wandered into the bush, or were perhaps given to Aborigines as gifts, if their owners made landfall in northern Australia.
"We need only imagine a lucky animal or two surviving the sinking of one boat near the coast of northern Australia to account for the genesis of Australia's dingo population." With the exception of Tasmania, dingoes spread rapidly. Aborigines hunted and ate them. And they were valued as companions and to warn of the approach of strangers.
But they were replaced rapidly by European breeds after colonisation, and, as well as being reviled as sheep killers, were blamed for the extinction on mainland Australia of the Tasmanian tiger and devil.
Johnson says this argument is based on circumstantial evidence: tigers and devils vanished from the mainland after dingoes arrived, but survived on Tasmania, which dingoes could not reach. Instead, he says that humans - again - were probably more to blame. He also notes that after Europeans arrived and Aboriginal hunting declined, the populations of other mammal species increased.
Koalas were virtually unknown in pioneering Victoria, but were abundant by the 1860s; tree kangaroos emerged from rainforest rarity to commonplace savanna in Queensland.
There have been similar booms across Australia - bilbies, possums, brush-tailed bettongs, rat kangaroos, wallabies, bandicoots, koalas and kangaroos have thrived in various parts of the continent as hunting declined and farmers created plentiful new sources of food and water.
Others suffered heavily. Johnson records the extinction of 18 mammal species in the past 200 years, and the exile of nine others from the mainland.
Most were "middle-sized" species of between 35g and 3.5kg, mainly native to the drier inland regions of the southern half of Australia. Most lived on the ground or in burrows or rock piles.
Johnson says this points to the real villains: red foxes and cats. Foxes were released for sport near the Victorian goldfield towns of Ballarat and Bendigo in 1870. With plentiful supplies of rabbits and hares - equally devastating to the fragile Australian environment - foxes raced across the continent. Whenever they arrived, other local mammal species went into steep decline.
"The current distribution of the fox in Australia provides a close, though not perfect, match with the geography of mammal extinction," Johnson says. Feral cats have been just as devastating. One study found as many as 10 species of native mammals disappeared from western New South Wales after cats arrived.
"I think it is fair to say that had foxes and cats never been brought to Australia, none of the recent mammal extinctions ... would have happened," Johnson says.
They thrived on the booming spread of rabbits, and were saved by farmers from the only predator that could keep them in check - dingoes.
Across Australia they were exterminated as sheep-killers. Wherever dingoes are rare, foxes are the most abundant. The vast dingo fence built on the border of NSW and South Australia to stop the spread of the dog gives a stark example: on the NSW side, where dingoes have been eradicated, the density of foxes is up to 20 times higher than on the SA side.
Dingoes compete with foxes for food, often more successfully. They also kill foxes, partly for food and partly for spite: "Dingoes go out of their way to kill foxes whether they eat them or not. Just as dogs hate cats, dingoes evidently hate foxes."
Similarly, cats are rare where either dingoes or foxes are abundant.
And Johnson says that, having taken over from the thylacine (Tasmanian Tiger) as Australia's largest predator, and from the devil as the only large mammalian scavenger, dingoes have become more important. They help control, for example, the massive kangaroo populations that thrive on the continent's farmland.
"The dingo is clearly an ecologically significant species that interacts strongly and stably with other native mammal species," Johnson says.
"But it has not been implicated in any extinctions of native mammals other than the thylacine and the devil - and the evidence linking the dingo to these extinctions is weak."
* Australia's Mammal Extinctions: a 50,000 year history, by Professor Chris Johnson, Cambridge University Press Australia, A$49.95 ($56).
