I took the first story as the tiger representing Pi and Pi representing God.
The tiger kept pushing Pi away, rejecting him and showing out right animosity. Eventually, he learned to trust Pi and realize he needed Pi in such a desperate situation.
In the end, once Pi helped the tiger get through the tough times, the tiger turned his back on Pi and felt he didn't need Pi anymore since he was in essence saved and could handle things on his own at that point.
I think a lot of that is how people turn to God in a crisis, but turn their backs once they're in the clear.
I'm not a religious person and never read the book, so I could be way off base.
