Koalas are forest dwellers, spending their lives almost entirely within the canopy of trees across eastern Australia. These iconic marsupials (Phascolarctos cinereus) are highly specialized for an arboreal existence, relying on the forest for every aspect of their survival. The specialization of their diet and anatomy means they cannot simply live in any forest, but must inhabit a specific type of woodland community.
The Essential Eucalyptus Connection
Koalas are folivores, meaning their diet consists almost exclusively of the leaves from certain Eucalyptus species. This specialization defines the type of forest they inhabit. Eucalyptus leaves contain chemical compounds, such as phenolic compounds and terpenes, that are toxic to most other mammals. Koalas have evolved highly specialized livers that metabolize and detoxify these chemicals.
This diet presents a challenge, as eucalyptus leaves are low in nutritional value. To compensate for the poor energy content, koalas must consume between 200 to 500 grams of leaves daily. The leaves also provide nearly all the moisture the koala needs, which is why the species rarely drinks water. This requirement for food and hydration makes the presence of suitable eucalyptus trees the determinant of a koala’s home range.
Geographical Range in Australia
The natural distribution of koalas depends entirely on the presence of appropriate eucalyptus woodlands across eastern and southeastern Australia. Koalas are found throughout Queensland, New South Wales, and Victoria, as well as in a small area of South Australia. Their range spans from cooler, heavier-bodied koalas in the south to smaller, lighter-colored populations in the north.
The koala’s habitat extends across approximately one million square kilometers, encompassing both tall eucalypt forests and low eucalypt woodlands. Their absence from Western Australia and Tasmania is due to the historical lack of the specific eucalyptus species they require. Within their range, koalas are found in higher densities where food trees grow on fertile soils or along watercourses.
An Entire Life Spent in the Canopy
Koalas are adapted for their arboreal lifestyle, possessing specialized features that allow them to climb and grip. Their forepaws feature five digits, two of which are opposable thumbs that function like a pincer to secure a powerful hold on branches. The hind paws have a large, opposable digit for extra grip, while the second and third toes are fused together to form a double claw used for grooming.
Their low-energy diet dictates a sedentary existence, as they must conserve energy while processing tough leaves. Koalas rest or sleep for up to 20 hours each day, often wedged in a tree fork. Their movement is typically slow and deliberate. They only descend to the ground when they must move between trees or during mating, though they can move quickly when disturbed.
Why Specific Forests Are Critical for Survival
For koalas, the forest is a life support system, making the loss or degradation of their habitat the primary threat to their survival. The specialization of their diet means they cannot simply relocate to a different type of forest when their home is cleared. Human activities like urban expansion and land clearing result in habitat fragmentation, breaking up large, contiguous forests into smaller, isolated patches.
Fragmentation forces koalas to spend more time on the ground moving between isolated tree patches, exposing them to risks. While on the ground, they are vulnerable to being struck by vehicles or attacked by domestic dogs. The stress caused by vulnerability and the loss of food sources can also make koalas more susceptible to diseases. Protecting these eucalyptus woodlands is essential due to the highly specific nature of their habitat requirements.