The dingo ... poison or let flourish?
Credit: Karen Johnson
Native Australian mammals generally reproduce much more slowly than rabbits, cats and foxes - an adaptation to prevent overpopulation in the arid Australian environment, where food can be scarce and unreliable - and populations decline because they can't grow fast enough to replace animals killed by the predators. Dingoes are the solution to this problem, says Johnson, because of how they interact with animals lower down on the food chain.
Dingoes are real bullies to cats and foxes, he says. Besides regularly eating the smaller predators, dingoes will slaughter them simply to lessen competition, steal their kills, and keep them from getting at food sources. Even the presence of dingo faeces can keep foxes away from potential prey.
As well as suppressing cat and fox populations, dingoes also regulate the numbers of kangaroos - animals too large to be affected by the small invasive predators. Dingoes keep them at moderate levels and prevent populations from going through 'boom and bust' cycles in response to changes in the environment. In areas where dingoes are baited, kangaroos can reach densities several times higher than in places where the dogs are free to hunt.
Dingoes put less pressure on smaller native mammals than do cats and foxes, according to Johnson, because dingo packs live in large, stable territories and generally have only one breeding female. This social structure limits their rate of increase, and thus their capacity for overpopulation. In the 4,000 years that dingoes have been in Australia, they have contributed to few, if any, mammal extinctions, he says.
Thousands of kilometres south and east of Carlton Hill lies Cameron Corner, a spot in the middle of the Strzelecki Desert marking the intersection of the states of South Australia, Queensland and New South Wales. Reaching out from this desolate spot for 2,500 km in either direction is the world's longest fence, standing two metres high and stretching from Jinbour in Queensland to the Eyre Peninsula on the Great Australian Bight in the south. Though its name changes twice as it meanders through the Australian outback, its purpose does not; the fence is there to keep dingoes out of southern Australia.
Though the barrier has been only partly successful in excluding dingoes from the south, it does split the two main types of livestock found on the continent: to the north of the fence, cattle predominate. To the south, sheep fill the landscape. In fact, Australia is a land dominated by the animals – 25 million cattle, 100 million sheep and only 20 million people.
Johnson can't see any way that dingoes could fit back into sheep country south of the fence. "Dingoes and sheep can't really co-exist because sheep are so easy for dingoes to kill that they'll hunt sheep in preference to anything else. If we've got sheep, we have to control dingoes."
