for National Geographic News
For example, St. Bees Island off the coast of Queensland is changing from "a koala-friendly forest to a koala-unfriendly forest," said Alistair Melzer, an ecologist at Central Queensland University (map of Australia).
Melzer has studied koalas for nearly 20 years and the St. Bees Island koalas for 8 years.
Koalas exclusively eat the leaves of eucalyptus trees. There are more than 700 species of eucalyptus, but the marsupials prefer the leaves of only a handful.
As the favored eucalyptus species disappear from the forest, St. Bees Island will eventually become unsuitable for the koalas and the resident population will likely go extinct.
Until recently, the St. Bees population had been considered unusually stable, and was intended to serve as a model for helping struggling populations elsewhere in Australia.
But the island's habitat shift is a new twist for land managers to consider as they set the nation's conservation priorities, Melzer said.
They have to ask, for example, "Do I try to go in there and manage these areas—effectively garden them for koalas or another target species. Or do I simply say, Well, that's life, and let them go?"
As humans settled and sculpted the Australian landscape to fit their needs over the past two centuries, koala habitat has become increasingly fragmented, Melzer said.
(Do you know what habitat you live in? Find out with our guide to Earth's ecosystems.)
"We're seeing, in a lot of cases, where koalas are in preserves of some sort. But the structure and composition of those habitats are changing, simply because that's what forests do," Melzer said.
SOURCES AND RELATED WEB SITES