Follow the relationship between Pi and Richard Parker. They endure over two hundred days of hardship together, but in the end Richard Parker leaves...

When Pi and Richard Parker are at the beginning of their journey, after Pi's family is killed in the shipwreck, Pi fears Richard Parker, but he is forced to find a way to co-exist with him in order to survive.  Over time the two develop a somewhat co-dependent relationship.  Richard Parker depends on Pi to feed him by catching fish, while Pi's will to live is bolstered by Richard Parker's presence.  Richard Parker recognizes that he also needs Pi to survive.  At one point in the book, Pi's starvation and thirst reduce him to a state where he is blind and nearly comatose.  An intruder, who also states he has been lost at sea, comes aboard his raft and tries to kill him and take his remaining supplies.  Richard Parker attacks and kills the intruder, saving Pi.  This event seems to imply that Richard Parker has developed similar feelings of love and dependence toward Pi.  Pi begins to see the journey as a hardship he has endured with Richard Parker; however, once he is able to reach land, Richard Parker turns and leaves without saying goodbye.  Pi feels abandoned because after his long ordeal with Richard Parker he has become emotionally invested in the tiger.  Richard Parker, however, perhaps was not truly emotionally invested in Pi.  It seems from Richard Parker's actions at the end of the book that his protection of Pi was motivated merely by his own survival instinct.  While they were lost at sea, Richard Parker needed Pi to survive, but now that they had reached the shore and Richard Parker could return to the jungle, he no longer needed Pi.  Pi, however, still had lost his family and now, abandoned by Richard Parker, truly felt he had nothing left.