What animals do koalas compete with?

There are no species that compete exclusively with the koala in its unique niche. While ringtail possums and greater gliders are capable of feediemu on eucalyptus leaves, they do not feed only on eucalyptus leaves. Also, koalas do not nest in treee hollows, but rather spread out on tree branches, so they do not compete for shelter with other species.

Man has encroached upon the koala's habitat, so it could certainly be said that they compete with man for territory - but they have no chance of coming out the victor in that battle.