Helen Morgan, University of New England; Guy Ballard, University of New England, and John Thomas Hunter, University of New England
Dingoes have often been hailed as a solution to Australia’s threatened species crisis, particularly the extreme extinction rate of the country’s small mammals.
But are dingoes really the heroes-in-waiting of Australian conservation? The truth is that no one knows, although our recent research casts a shadow over some foundations of this idea.
The notion of dingoes as protectors of Australian ecosystems was inspired largely by the apparently successful reintroduction of wolves into Yellowstone National Park in the United States. But Australia’s environments are very different.
To understand the recent excitement about wolves, we need to consider an ecological phenomenon known as “trophic cascades”. The term “trophic” essentially refers to food, and thus trophic interactions involve the transfer of energy between organisms when one eats another.
Within ecosystems, there are different trophic levels. Plants are typically near the base; herbivores (animals that eat plants) are nearer the middle; and predators (animals that eat other animals) are at the top.
The theory of trophic cascades describes what happens when something disrupts populations of top-order predators, such as lions in Africa, tigers in Asia, or Yellowstone’s wolves.
The wolves’ decline allowed herbivores, such as elk, to increase. In turn, the growing elk population ate too much of the shrubby vegetation alongside rivers, which, over time, changed from being mostly willow thickets to grassland. Then another herbivore – beavers – that relies on willows went locally extinct. This in turn affected the ecology of the local streams.
Without beavers to engineer dams, local waterways changed from a series of connected pools to eroded gutters, with huge flow-on effects for smaller aquatic animals and plants.
Now, the reintroduction of wolves appears to have reduced the impact of elk on vegetation, some riparian areas have regenerated, some birds have returned and there are signs of beavers coming back. That said, wolf reintroduction has not yet fully reversed the trophic cascade.
Comparing apples with quandongs
Sturt National Park, in the New South Wales outback, has been nominated as an experimental site for reintroducing dingoes. Recently, we compared the environment of Sturt with Yellowstone to consider how such a reintroduction might play out.
These regions are clearly very different. Both are arid, but that is where the similarity ends. Yellowstone has a stable climate and nutrient-rich soils, sits at high altitude and features diverse landscapes. Precipitation in Yellowstone hasn’t dropped below 200mm per year in more than a century.
Yellowstone’s precipitation falls largely as heavy winter snow. Each spring the snowmelt flows in huge volumes into rivers, streams and wetlands across the landscape. This underpins a predictable supply of resources which, in turn, triggers herbivores to migrate and reproduce every year.
These predictable conditions support a wide range of carnivores and herbivores, including some of North America’s last-remaining “megafauna”, such as bison, which can tip the scales at over a tonne. Yellowstone also has many large predators – wolves, grizzly bears, black bears, mountain lion, lynx and coyotes all coexist there – along with a range of smaller predators too.
Predators in Yellowstone can be sure that prey will be available at particular times. The environment promotes stable, strong trophic links, allowing individual animals to reach large sizes. This strong relationship between trophic levels means that when the system is perturbed – for instance, when wolves are removed – trophic cascades can occur.
Unlike Yellowstone, arid Australia is dry, flat, nutrient-poor and characterised by one of the most extreme and unpredictable climates on Earth. The yearly rainfall at Sturt reaches 200mm just 50% of the time.
Australia’s arid ecosystems have evolved largely in isolation for 45 million years. In response to drought, fire and poor soils, arid Australia has evolved highly specialised ecosystems, made up of species that can survive well-documented “boom and bust” cycles.
Unlike the regular rhythm of Yellowstone life, sporadic pulses of water and fire affect and override the trophic interactions of species, between plants and herbivores, and predators and their prey. Our native herbivores travel in response to patchy and unpredictable food sources in boom times. But however good the boom, the bust is certain to follow.
Unpredictable but inevitable drought weakens trophic links between predators, herbivores and plants. Individuals die due to lack of water, populations are reduced and can only recover when rain comes again.
Our arid wildlife is very different from Yellowstone’s too. Our megafauna are long gone. So too are our medium-sized predators, such as thylacines.
Today, arid Australia’s remaining native wildlife is characterised by birds, reptiles and small mammals, along with macropods that are generally much smaller than the herbivores in Yellowstone.
Our predators are small and mostly introduced species, including dingoes, foxes and cats. None is equivalent to wolves, mountain lions or bears, which can reach more than three times the weight of the largest dingo. Wolves are wolves, and dingoes are dogs.
Wolves in dingo clothes?
What does all this mean for Australia? Yellowstone’s stable climate means that there are strong and reliable links between predators, prey and plants. By comparison, arid Australia’s climate is dramatically unstable.
This raises the question of whether we can reasonably expect to see the same sorts of relationships between species, and whether dingoes are likely to help restore Australia’s ecosystems.
We should conduct experiments to understand the roles of dingoes and the impacts of managing them. How we manage predators, including dingoes, should be informed by robust knowledge of local ecosystems, including predators’ roles within them.
What we shouldn’t do is expect that dingoes will necessarily help Australia’s wildlife, based on what wolves have done in snowy America. The underlying ecosystems are very different.
Many people are inspired by the apparently successful example of wolves returning to Yellowstone, but in Australia we should tread carefully.
Rather than trying to prove that dingoes in Australia are just as beneficial as wolves in Yellowstone, we should seek to understand the roles that dingoes really play here, and work from there.
Helen Morgan, Phd candidate, Ecology, University of New England; Guy Ballard, Adjunct Senior Lecturer, University of New England, and John Thomas Hunter, Adjunct Associate Professor in Landscape Ecology, University of New England
This article was originally published on The Conversation. Read the original article.