Return of devil could aid small mammals in Australia

Ecologically speaking, Australia is a bit like a crazy quilt, a patchwork of globally unique fauna overlain by the effects of two waves of human settlement (first by Aboriginal people and later European colonists), accidental introductions of invasive species, deliberate but often ill-advised introductions of others, and still other species driven out.

Now, researchers from the University of New South Wales have proposed repairing a fraying patch of the continent’s ecology with an unexpected bit of native fabric. Mathematical modeling shows that the Tasmanian devil (Sarcophilus harrisii) could fulfill the ecological role once played by dingoes (Canis lupus dingo) in certain areas, they report in the journal Biological Conservation.

The Tasmanian devil is a carnivorous marsupial about the size of a small dog, with a stocky body, black fur, and rounded ears. Devils were once widespread throughout Australia, but disappeared from the mainland about 3,000 years ago. Many scientists believe they were extirpated by the dingo, a semi-wild dog that arrived on the continent between 3,500 and 5,000 years ago. Today, devils survive only on the island of Tasmania, which dingoes never colonized.

Dingoes themselves have now been eradicated from some parts of Australia, because they are perceived as a threat to domestic livestock. But their removal has caused a cascade of ecological problems. In the absence of this apex predator, increased populations of grazing herbivores such as kangaroos and wallabies consume large amounts of low-lying vegetation. This makes small and medium-sized native mammals more vulnerable to foxes and cats, invasive predators that also increase in numbers when dingoes aren’t around.

In short, Australia’s ecology has become unbalanced, and the continent needs an animal that can fill the top predator niche. “The devil is the obvious answer,” says Daniel Hunter, a graduate student in the School of Biological, Earth, and Environmental Sciences and the study’s lead author.

The researchers identified southeastern Australia as a promising place for devil reintroduction because the relatively cool, wet climate is similar to that of its existing habitat in Tasmania. Dingoes are absent from many parts of this region, so they wouldn’t pose a threat to devil populations – plus, areas without dingoes are precisely the ones most in need of a top predator.

The researchers’ models show that adding devils to this landscape of eucalyptus forests and agricultural lands would reduce the abundance of cats and foxes; increase the complexity of low-lying vegetation; and increase populations of some small mammals such as bandicoots, greater gliders, ringtail possums, bush rats, and a group of mouse-like creatures known to scientists as Antechinus.

Researchers have also proposed reintroducing dingoes as a top predator, but this could be a hard sell with ranchers, who may prefer the devil they don’t know to the dingo they do.

Reintroduction could also improve the chance of survival for the devil itself, which is an endangered species. Devils on Tasmania have been ravaged by devil facial tumor disease, a transmissible form of cancer, and establishing a disease-free population on the Australian mainland could provide the species with a measure of insurance against extinction.

But not all native species would benefit from devil reintroduction, the researchers found. “Devils aren’t a silver bullet,” says Mike Letnic, associate professor in the School of Biological, Earth, and Environmental Sciences and the study’s senior author. They might restore balance to the ecosystem as a whole but provide little benefit to the most threatened mammals, such as quolls and rock wallabies, because these species are the ideal size for devil prey.

More broadly, the study brings up one of the most enduring and often vexing questions in restoration ecology, that of deciding: restoration to what? Usually, the benchmark for restoration is pre-human or at least pre-European-colonization, but in this case reintroducing the Tasmanian devil to areas without dingoes might recreate some aspects of the continent’s pre-dingo ecology. That’s not the goal of these efforts of course, but the proposal points to the complexities often inherent in this area of conservation biology. Still, in the crazy quilt of the real world, sometimes a strange and unlikely pattern is exactly what works. – Sarah DeWeerdt | 25 August 2015

Source: Hunter D.O. et al. “Reintroduction of Tasmanian devils to mainland Australia can restore top-down control in ecosystems where dingoes have been extirpated.” Biological Conservation DOI: 10.1016/j.biocon.2015.07.030

Header image: A Tasmanian devil (Sarcophilus harrisii). Credit: jomilo75 via Flickr.