When discussing the animal kingdom, each creature resides on a species scale of generalists to specialists. Specialist creatures like the koala bear can only survive on an extremely limited set of conditions: diet (eucalyptus), climate (warm), environment (trees). Generalists, on the other hand (think mice) are able to survive just about anywhere. They can withstand heat and cold, eat your organic breakfast cereal or seeds and berries foraged in the wild.
