Koala numbers reached a low point in the 1930s, when hunting for the fur trade made many local populations extinct, including that in South Australia. Other factors in their decline included land clearing, disease, fire and drought. Whilst the koala population as a whole has recovered somewhat since then, its current conservation status varies across its range (3).
Major threats to the mammals now include land clearing and urbanization, which result in the loss, fragmentation and degradation of habitats. The koala is confined by its diet to a specialised habitat, of which around 80 percent has been destroyed since Europeans settled in Australia. It is also threatened by fires, droughts and disease (particularly due to the Chlamydia bacterium) (4), while around 4,000 koalas are thought to be killed each year by collisions with road traffic and predation by dogs (8). Recently there has been a lot of attention in the media suggesting that koalas in some isolated patches of habitat have been the cause of defoliation of eucalyptus trees, resulting in calls for a cull of the koalas in these areas. That the koalas are to blame is a contentious issue amongst scientists and authorities and there is evidence to suggest that several other factors may be the cause (4).
Global climate change has been identified as a further threat to the koala. Climate change is predicted to result in increased atmospheric carbon dioxide levels, which causes plants to grow faster. This reduces protein levels in plants and increases tannin levels. As carbon dioxide levels continue to rise, the koala will need to cope with increasingly nutrient-poor and tannin-rich eucalypt leaves. The koala may respond to this by travelling further in search of the most nutritious leaves. However, dispersing koalas will be at increased risk of predation and will often find themselves having to cross main roads and coming into contact with domestic animals (8).
Climate change is predicted to cause an increase in drought frequency and fire-causing weather in many parts of Australia, owing to reduced rainfall levels, increased evaporation rates and an overall temperature increase of about 1 degree Celsius by 2030. Koalas are particularly vulnerable to bushfires as their slow movement and tree-dwelling lifestyle makes it difficult for them to escape and their food supply can be destroyed. Their lack of mobility and specialisation upon specific tree species also makes them extremely vulnerable to droughts (8).