We’ve just noticed Australia’s mammals are going extinct
Australian wildlife shouldn’t be going to extinct. For one thing, Australia is relatively devoid of humans. There are just three people per square kilometer, which is extremely low compared to the global average of around fifty people per square kilometer. Most of the continent is undeveloped and unsettled. Vast swaths of the continent combine to form one of the world’s largest natural environments. Throughout most of the world, conservation concerns fall upon relatively poor nations who simply can’t afford to devote resources to biodiversity. But Australia is a relatively affluent nation. By most metrics, Australian wildlife – some of the most unique in the world, as 87% of the continent’s terrestrial mammals are endemic – should be doing just fine. So why isn’t it?
According to an argument laid out this week in the journal PNAS by Charles Darwin University researcher John C. Z. Woinarski, Australian Department of Parks and Wildlife research fellow Andrew A. Burbidge, and Southern Cross University marine ecologist Peter L. Harrison, it all started in 1788. That’s when Australia became the focus of European settlement.
But, as Woinarski and his colleagues point out, it’s not as if Australia was a garden of Eden prior to European settlement. A hundred thousand years of evidence in the fossil record shows drastic declines in the island’s megafauna, presumably owing to climate changes, hunting by the Aboriginal people, and possibly fire management by the Aboriginals as well. Then the introduction of the dingo some 3,500 years ago also probably changed the continent’s ecosystems due to the addition of an unfamiliar predator.
But the 227 years since European settlement began represent a dramatic acceleration in ecological disruption. More than 10% of Australia’s endemic land mammals have gone extinct in that time. That’s 29 out of 273 species confirmed extinct, with at least one additional probable species that hasn’t been spotted in at least thirty years, the Christmas Island shrew. Another non-endemic species, the western long-beaked echidna, is completely extirpated and barely hangs on to existence as a critically endangered species in New Guinea.
According to Woinarski’s analysis, Australia’s land mammals have gone extinct at the rate of 1-2 species per decade since sometime around 1840 when the first species became extinct following European settlement. By comparison, North America has had only one terrestrial mammal extinction since European settlement: the sea mink, Neovison macrodon.
Things aren’t looking too bright for those species that remain, either. The trend of losing 1-2 species per decade doesn’t appear to be slowing down. Fifty-six terrestrial mammals are red-listed by the IUCN as threatened, and another 52 are classified as near threatened. Combined, they represent 47% of Australia’s terrestrial mammalian biodiversity.
Most of these extinctions, argue the researchers, can be blamed on introduced mammal predators: cats and foxes. But there’s a confluence of other factors as well. For example, introduced prey items also take their toll. The poisonous Central American cane toad is continuing to wipe out one of its would-be predators, the northern quoll. Then there’s the devil facial tumor disease, which is currently devastating the largest surviving marsupial carnivore, the Tasmanian devil. The Leadbeater’s possum lost nearly half the entire species during a single week because of a single wildfire in 2009, though it was already restricted to just some 2200 individuals.
Then there are the introduced herbivores. “Pastoralism based on introduced sheep and cattle is now the dominant land use across much of Australia,” the researchers say, which not only results in habitat degradation for native species, but also results in competition for native herbivores over the same vegetation. And that’s to say nothing of all the rabbits, goats, donkeys, camels, horses, and buffalo.
More direct threats from humans – persecution and exploitation – have “substantially reduced the abundance” of terrestrial mammals like koalas and kangaroos and marine mammals like seals and whales, though there is thankfully “no substantial ongoing hunting of any threatened Australian mammal species.” So that’s at least one threat that’s reduced, rather than intensified, since European settlement.
Given all of that bad news, two questions arise. First, can anything be done? And second, how can it be that nobody really noticed?
As for the first, the researchers argue that the only effective strategies will be large-scale and long-term. Localized and short-term conservation efforts will be met with only limited success. Assistant colonization, they say, which involves the transportation of threatened mammals to safer locations can be successful. Historically, “this is mainly involved the ‘marooning’ of threatened mammals on islands, on which feral predators have never been introduced or have been eradicated.” Think: Jurassic Park but for tiny adorable rodent-sized marsupials. They argue that similar “mainland islands” could be created, where fences keep primary threats away. Still, the greatest benefit to the continent’s endemic mammals would be the eradication of feral cats. The challenge, of course, would be to control the island’s feral cat population without harming pet cats or other wildlife. “It is,” the Woinarski and colleagues acknowledge, “a formidable problem.”
As for the second question – how is it that nobody really noticed the severity of mammalian decline in Australia – the answer is a bit more straightforward. “Other than the iconic thylacine,” write Woinarski, Burbidge, and Harrison, “Australians, and the global community generally, have been relatively oblivious of this extinction calamity. In part, this is because many of the now lost species were obscure, small, nocturnal, and shy, and lived remote from most human settlement.” In other words, human communities simply didn’t have the wildlife literacy to know who was living alongside them. Just because the Australian Outback is expansive and appears unsullied does not mean that its ecosystems are healthy.
It is perhaps of little comfort that that sort of nature illiteracy may finally change only now that the most charismatic of endemic mammals, like koalas and platypuses, are becoming increasingly threatened. – Jason G. Goldman | 11 February 2015
Source: “Ongoing unraveling of a continental fauna: Decline and extinction of Australian mammals since European settlement,” by John C. Z. Woinarski, Andrew A. Burbidge, and Peter L. Harrison. PNAS.
Header image: The endangered northern quoll, a mammal species native to Australia. Image courtesy of Jonathan Webb.
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