Because of his zoo-keeping background, Pi is able to control, manage, and strike fear in the heart of Richard Parker, a ginormous Bengal tiger who is surviving on a tiny lifeboat with him.  He realizes first off that he has to somehow get Richard Parker to understand that it is he, Pi, who is the alpha male on the boat, which also puts him under the category of "do not eat."  So, he institutes a classical conditioning training method:  the whistle.  Any time the tiger even seems to be thinking about crossing into Pi's "territory" on the boat, he blows the whistle, which startles Richard Parker, scaring him back.  Then, whenever Pi feeds Richard Parker, he blows the whistle, establishing the connection that Pi is the master, the provider, and the all-powerful supplier of food.  These tricks save Pi's life, and Richard Parker's life since it allows Pi to survive and get food for him.

Pi also uses his background in figuring out way to obtain and eat food, and in other elements of survival.  But the main way it plays out is in dealing with Richard Parker.  In fact, if he hadn't had the background that zoo-keeping and a wise father had given him, he probably would have been a Pi-sized snack for Richard Parker pretty early on in the story.