Koala distribution, genetics and disease, the science and the other

Co-coinciding with news that the Victorian government is to ‘cull’ another 400 koalas at Cape Otway, the Royal Zoological Society of New South Wales has published a paper about koalas at Campbelltown titled, ‘A dangerous idea: that Koala densities can be low without the populations being in danger’.

While Cape Otway is a long way from Campbelltown there are two things these koalas share, both populations have been through a ‘genetic bottleneck’ and neither has Chlamydia. As indicated in the koala distribution map below, koalas in the green ellipses do have Chlamydia, where those with a red outline do not. The majority of Victorian koalas don’t carry Chlamydia and although one koala has been found with Chlamydia in the Northeast Monaro population, whether the disease is widespread in the population/s is not known, so it’s outline is black.

The major factor influencing populations without the disease is the ability to breed every year, so populations rapidly increase where suitable browse exists. Hence the issues with Cape Otway and other tanslocated koalas. However the Cambelltown koalas inhabit lower quality forests. The concern is that these koalas could catch Chlamydia from adjacent populations, potentially wiping them out. So it’s been suggested that these koalas be managed separately from other populations. Similarly, koalas in South Gippsland are genetically distinct from the ‘bottleneck’ koalas and separate management for these koalas has also been suggested.

Exactly what the NSW government will do remains unclear, but with forestry involved the science tends to get left behind.


Speaking of forestry, now retired forester Vic Jurskis has published a book titled ‘Firestick Ecology’, where he once again espouses the view that more burning is needed. In an interview with ABC radio Vic says “You see it right across the landscape. With lack of fire you’ve got declining trees, scrub, pests, parasites, and diseases.” So I had a bit of a discussion with Vic on ABCSE’s facebook page, his last comment is printed below. As indicated Vic thinks koalas are parasites, that do best in declining forests. While providing  several examples to back up his case, it doesn’t make much sense because logically if koalas do better in unhealthy forests there should be many more than there are.

In addition, if there were no koalas on the Cumberland Plain or the Bega valley at the time of European settlement, where did they come from? At this point one could ask the OE&H, but according to one source Koala recovery officer Chris Allen is quoted as saying ‘(he)  thinks the South East koalas might be adapted mountain animals that were able to survive because they retreated from or were not caught up in the clearing of lowlands for farming.’

So it’s probably best to stick with the scientific advice and hope the government eventually takes it on.

“. . . The densities of koalas in the open red gum woodlands of the Cumberland Plain and the Bega valley were zero at the time of European settlement.Chronic eucalypt decline leads to irruptions of koalas where there are species of trees such as red gum that are preferred by koalas, in sufficient numbers. Where there are mainly species that are not preferred by koalas, other arbivores such as psyllids irrupt. Where psyllids irrupt, things that eat psyllids, such as bellbirds also irrupt. For example, with greatly reduced burning at Urbenville in the 1980s and 90s, the area of chronically declining forest increased by 20,000 hectares and koalas became the most common arboreal mammal, being found at 50% of survey sites in the forest.” Vic Jurskis.


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