A brief history of the koalas of South Australia

A quintessentially Australian mammal, the koala is revered as a national icon and although it is categorised under ‘Least Concern’ on the IUCN’s Red List, some experts believe the species will face extinction sometime in the next 50 to 100 years.

This week, South Australia’s minister for sustainability, environment and conservation, Ian Hunter, announced a ‘new plan to protect our koalas’ via a press release. It lists the threats that koalas in general face, while also boasting an estimated local population of ‘about 114,000 koalas in the Adelaide Hills and Mount Lofty Ranges’. As such, the statement could be taken to imply that South Australia’s koalas might serve as an insurance population for the entire species.

But first, South Australia’s koala population needs to be adequately protected, and so Hunter has also announced a new koala management strategy that is now available for public comment.

“This new conservation and management strategy looks at ways we might be able to reduce these impacts and ensure their long term future in South Australia and we are asking the public for input on this plan to ensure it reflects the views of the community.”

It’s hard to imagine the people of South Australia looking at any plan to assist their local koalas in any way other than favourably, yet opinions may vary regarding what exact methods will yield the most effective and sustainable results.

Is the Koala Threatened?

While the IUCN does categorise the species under ‘Least Concern’ the government has independently classified populations in Queensland and NSW as ‘Vulnerable’, with major threats including deforestation and habitat fragmentation, fire, disease, dog attack and car strike all having a deleterious effect on the koalas of the eastern seaboard. As these threats are often interlinked, it’s difficult to single out any single point of focus when considering how to tackle the problem.

In particular, deforestation in Australia represents an ever-present pressure that garners perennial coverage in both domestic and international media. However, the true extent to which Australia’s forests have been obliterated can’t be overstated.

Professor Corey Bradshaw of the University of Adelaide has conducted research into both deforestation as well as South Australia’s koala population. His 2012 paper, ‘Little left to lose: deforestation and forest degradation in Australia since European colonization‘, found that not only has our country already lost almost 40 per cent of its forests, but that the remainder has also been severely fragmented.

When speaking with Wild, Bradshaw highlighted the lost of forests along the east coast as an underlying problem for the koalas that live in those regions.

“The greatest rates of forest clearing has occurred in southeastern Queensland and northern NSW since the 1970s, while Victoria is the most cleared of all states,” he said. “On the other hand, South Australia’s koala population arrived after the majority of clearing had occurred and they are therefore facing quite a different set of threats.”

Here, Bradshaw refers to the fact that the koala wasn’t actually present in Australia when European settlers first arrived. Instead, it is believed that the koala has gone extinct in the region since the late Pleistocene, perhaps 100,000 or more years ago.

“Since then, a small population was present in the southeast where South Australia borders Victoria,” Bradshaw explained, “but these animals would be more accurately defined as part of Victoria’s population.”

After the 19th Century fur trade greatly reduced koala numbers throughout Victoria, it was decided that the species would be introduced to South Australia. This resulted in just 18 individuals being released onto Kangaroo Island between 1923 and 1925. Since then, those numbers exploded to an estimated 27,000 in 2001. Furthermore, some individuals from Kangaroo Island were translocated to the Mount Lofty Ranges from 1959 to 1969.

“The University of South Australia’s koala count that was done in partnership with the CSIRO in 2012 helped us to model the potential population that have since colonised the Mount Lofty Ranges,” Bradshaw said. “With a 95 per cent confidence interval, we can say there are between 28,000 and 200,000 individuals in that region, with the median number of 114,000 cited as the government’s ‘estimate’.

“For this very reason, the koalas of South Australia aren’t threatened so much by deforestation, even though they are residing in what is essentially forest remnants. And yes, they are also faced by problems regarding fire danger, dog attacks and car strike. Ultimately, however, their major issue is one of low genetic diversity and inbreeding.”

Australia: The Land of Inbred Animals

The koala population in South Australia may currently be the highest it’s been in the past hundred millennia, yet those individuals are all very closely related, having been derived from just 18 individuals.

“It’s not very likely all of those 18 even contributed to the modern population, which has effectively been through two population bottlenecks in the last century,” said Bradshaw. “We’re not talking about koalas that are as closely related as, say, cousins. It’s brothers and sisters out there. There’s perhaps the equivalent of three or four individuals (in terms of genetic variety) in a population of many tens of thousands.”

Bradshaw’s concern for South Australian koalas is borne out in reports of unhealthy individuals, congenital defects and strange deformities. And while these animals have been sufficiently fecund enough to reach near-pest levels throughout the region, their maximum breeding and survival rates are still below what is considered average for the species.

“They’re so inbred, even a minor disease could wipe them out,” he warned.

Inasmuch as low genetic diversity is a problem for South Australia’s koalas, it is in fact a matter of some concern for the species as a whole. As koala populations are easily cut off from one another by rivers, roads and urbanisation projects, groups of these animals across the country are beginning to face the same inbreeding issues that is so accentuated in South Australia’s koalas. Bradshaw tells us that the last, most diverse population actually resides in Victoria’s South Gippsland region.

“The problem is by no means restricted to koalas, either,” Bradshaw explained. “Brown snakes, emus – there are many examples of geographically widespread Australian natives that have extremely low genetic diversity, and it’s not necessarily always the result of human interactions. Some of these animals have proliferated from naturally occurring population bottlenecks that happened thousands of years ago.”

The solution to the problem is by no means simple. Genetic variation, once lost, is practically impossible to regain without access to genetically distinct individuals. More importantly, there’s little point to such breeding programs if there isn’t suitable habitat for the species to repopulate.

In the case of South Australia’s new management strategy, Bradshaw recommends the government doesn’t need to do all that much to turn the local koala population into a truly useful insurance policy for the entire species.

“Obviously reforestation in certain areas would help immensely,” he said. “But first the genetic diversity issue must be addressed and this will require introducing a number of healthy individuals from genetically distinct populations. Until that happens, the entire species is at risk of total extinction in the wild over the course of the next 50 to 100 years.”