"Consequently, where you've got a fragmented population, we would expect to see populations disappear over a generation," Melzer added.
In southern Australia a lack of natural controls such as disease or predators allows some isolated populations to grow unchecked, outstripping the landscape, Melzer said.
(Related: "Koalas Overrunning Australia Island 'Ark'" [May 10, 2002].)
In the states of Queensland and New South Wales, however, various populations are decreasing.
"It's happening in a mosaic, in patches of koalas," Melzer said.
"Small populations are contracting and disappearing, so that the extent of the distribution of the species is still pretty good. But the overall distribution is getting thinner and thinner."
Left to fend for themselves, the marsupials may eventually disappear.
The Australian Environment Protection and Biodiversity Conservation Act officially lists koalas as "vulnerable" in New South Wales and southeast Queensland. "Vulnerable" is one step away from "endangered."
Melzer said the entire Australian population should be considered "at risk, however you formally describe that."
In addition to the habitat research, Melzer's St. Bees Island koala project aims to identify why the koalas there seem to live in tune with their surroundings while koalas in southern Australia outstrip their habitat.
His postgraduate student Gail Tucker has found that a loss of koala babies just after weaning appears to limit the island's population growth.
While the team is not sure why the young koalas die on St. Bees, the findings do rule out chlamydia as the population-control agent.
The disease causes sterility, so some experts had thought it might regulate koala populations by preventing some females from breeding.
Community members in regions where the animals outstrip the forests have recommended introducing chlamydia to koalas to keep them from having more babies and growing their populations to unsustainable levels.
"All they'll be doing is causing pain and suffering to animals to whom the disease is new," Melzer said.
Deborah Tabart is the chief executive officer of the Australian Koala Foundation in Brisbane.
She said conservation of the species requires a big-picture approach rather than micromanagement of isolated habitats.
The decades of land clearing for farms and houses, damming of rivers, and now the drought and fires have "changed the landscape dramatically," she said.
"We have to change our behavior, the whole world. We're the ones causing this," she added.
"I feel that when we continually say, Oh, we'll move the koalas [to another habitat], we'll do whatever—I just think that's fiddling while Rome burns."
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