They are two versions of the story. The one with animals which reprsents the humans and the one with out animals, in both versions pi narates his experience symbolising his journey and the events that took place with in. In the version of animal; Pi reprsent himself as the bengal tiger as the animal and his humanity as himself trying to tame the animal. In human version, there are only 4 survivors on the boat but with the animals there were 5. The whole journey in each version are parallel to each other .
The island symbolizes Pi' mothers body and the mere cats reprsents the maggots. The island is carnivorus reprsents canibalism and also state of Pi's mind which is also decaying. In the island the tiger and him are in harmony... because at near death condition, Pi lost himself with in the animal
The religion is the forgivness and sign of god that pushed him away from the island by the tooth he found.
The hyena partially ate the zebra and killed the orangutan but it was the tiger who ate them all. Pi is the tiger.
The journey with animals reprsents humananity in its all forms of sprituality and hope. Which helps Pi from falling in to despair and guilt. Also aids him in moving on with life
Where as the human version reprsents the survival inhuman instinct in its rawest form.