In the early 1900s, Australia began to build a fence that now stretches for some 3480 miles across the states of South Australia, New South Wales, and Queensland. It is called the “Dog Fence” and its purpose is simple: keep voracious dingoes away from farmers’ livestock. Though it's successfully shut the canines out, as Emma Marris reports for Nature, a new study suggests that this artificial barrier has altered the ecosystems of Australia’s outback.
The study, published in Proceedings of the Royal Society B, focuses on trophic cascades—when the addition or removal of top predators causes a ripple effect of changes within an ecosystem. Decreasing the number of carnivores, for instance, leads to a proliferation of herbivores, which in turn affects vegetation and soil composition.
Researchers at the University of New South Wales wanted to find out if limiting the number of dingoes on one side of the Dog Fence has created such changes in the area’s landscape. But to do this, they had to first count the number of dingoes and kangaroos—the canines’ favorite snack—on either side of the fence.
According to a press release, the team spent four years driving along outback dirt tracks to count the animals. On the dingo side, researchers spotted a total of 85 dogs and eight kangaroos, Kelsey Kennedy reports in Atlas Obscura. But on the opposite side, there was just one dingo with some 3,200 kangaroos happily hopping about, unchecked by pesky predators.
To determine how this large kangaroo populations might affect vegetation, researchers set up 16 plots, with eight on either side of the fence. Four plots on each side were closed off to kangaroos. On the dingo side, closing the plots to the marsupials didn't have much effect on the vegetation. But on the other side, areas that were blocked off to kangaroos had about 12 percent more coverage.
By munching on plants, in other words, the herbivores were reducing the amount of vegetation coverage. But it's more than changes in plant coverage: this “over-grazing” has led to depleted soils, according to the study. Researchers found lower levels of phosphorus, nitrogen and carbon in the soil where kangaroos roamed in great numbers compared to areas where dingoes were common.
“We have shown for the first time that the presence of dingoes is linked to healthier soils, because they suppress the numbers of kangaroos that graze on the vegetation," said Professor Mike Letnic, senior author of the study, according to the press release. "Allowing dingo populations to increase could enhance the productivity of ecosystems across vast areas of the country by reducing herbivore numbers.”
Some experts, however, aren’t so sure that a trophic cascade is at work here. Benjamin Allen, a wildlife ecologist at the University of Southern Queensland in Toowoomba, told Nature’s Marris that other factors—like sheep and water availability—might account for differences in vegetation on either side of the fence.
Though it's unlikely dingoes will be released into the area anytime soon, the study serves as an important reminder that such large-scale changes of the landscape often come with unintended consequences.