The koala is known to be a solitary creature.  Within its own species, the only time when there is more than one koala in a certain area is when the mother is taking care of her joey or during the mating season.  The joey stays with the mother for about a year, and after that is expected to retreat to its own home range.  During the mating season, male koalas approach female koalas in their home range.  Once the mating has occurred, however, the males leave and the females are left alone in their tree.

Koalas have few natural predators.  Many koalas are killed each year in dog attacks, though.  Humans are responsible for a great deal of koala deaths, as well.  It is very common for koalas to be run over by cars.  Also, massive deforestation by humans has lead to koala deaths. 

Help me, help you...

Koalas are dependent on bacteria to digest the fiber from the eucalypts leaves they consume (For more on this see the Nutrition section).  This is an important interaction because it allows the koalas to eat the eucalypts leaves that other animals cannot.  This allows for a decrease in competition for food between koalas and other organisms.  

Stress stings... 

In times of stress, koalas can contract and suffer from chlamydial infections (Learn more about this in Other Facts).  These bacterial infections spread very quickly and have serious consequences on the population.  This infection has been known to cause problems in koalas for quite some time, and in 1995 scientists were able to isolate the strains that were causing the problem.