MOST pastoralists consider wild dogs a threat to their profitability, but a group of ecologists is arguing for a different view.
Wild dogs eat kangaroos, and kangaroos eat grass. When researchers led by Thomas Prowse at the University of Adelaide sat down to assess how wild dog predation of kangaroos affected pasture growth, they found the sums often came out in pastoralists’ favour.
With wild dogs suppressing kangaroo numbers, the study authors argue, cattle graziers have more pasture generally, and less likelihood of a kangaroo explosion in flush times.
And at moderate stocking densities, sustaining populations of wild dogs to suppress kangaroo numbers has a clear economic benefit in cattle grazing operations, according to the researchers’ modelling.
It’s a view shared by Longreach grazier Angus Emmott.
“Assuming a typical stocking density for semi-arid rangelands, we estimated that kangaroo control by an unbaited dingo population would increase pasture biomass by 53 kg ha-1, improve gross margins by $0.83 ha-1, and reduce inter-annual variability in profits,” the researchers concluded.
If there are no wild dogs, lightening off on stock numbers often has little effect on total grazing pressure because kangaroo numbers expand to take advantage of the extra biomass.
In 2000, a south-western Queensland study found that kangaroos could eat up to 30–40 per cent of pasture growth.
The researchers found that the most viable scenario, an intermediate stocking rate with healthy populations of wild dogs to suppress kangaroo numbers, proposes a dynamic balance between biomass, cattle, kangaroos and wild dogs.
Calf losses were factored into the modelling. Losses are greatest when dingoes don’t have access to other forms of prey, the researchers observed, such as during drought.
At high cattle stocking densities, little feed remains for kangaroo populations to expand. If wild dogs are overabundant in this situation, the researchers acknowledge that tactical baiting might produce a small economic gain.
However, the paper says that there is seldom economic justification for dog baiting in cattle rangelands. It points to a 2002 report by Eldridge, Shakeshaft and Nano, which argued that baiting can actually increase stock losses because it disrupts the structure of dog packs and encourages more breeding among non-dominant pairs.
“On balance, therefore, we consider that even under the aforementioned conditions, our models provide little evidence to support dingo control in cattle rangelands,” the authors concluded.
The study only looked at cattle production, the authors acknowledging that “dingoes can kill sheep more easily than calves”.
However, their solution for sheep operations - protect sheep flocks with guardian animals - is a notion likely to be disputed by most sheep graziers.
The study adds to a global discussion about restoring “apex predators” to ecosystems.
Where predators have been removed from landscapes because of conflicts with livestock production, ecologists argue, population explosions of animals that the predators once suppressed tend to occur.
That’s led to experiments in “re-wilding”, where apex predators like wolves have been returned to parts of Europe and the Americas where they had once been driven extinct.
Re-wilding is unnecessary in Australia, where wild dogs show no sign of going extinct - often, the reverse.
But managing wild dogs to maximise their impact as an apex predator, while minimising their impact on livestock production, has proven a perennial challenge.
Humans tend to drive towards a binary solution - no dogs/no stock - but as with this paper, ecologists are increasingly saying that what might work best is the uncertain business of managing for a constantly shifting point of balance.
“Ecological and economic benefits to cattle rangelands of restoring an apex predator” will appear in the Journal of Applied Ecology. It can also be read online.