What sort of relationship has formed between Pi and Richard Parker?
Since this relationship comprises much of the novel, it is essential to understand this relationship.
It would appear that Richard Parker needs Pi more than Pi needs him. Without Pi providing food to the tiger, the tiger would kill him, then die. In the wild, Pi would be fair game but because he is zoo tiger, he must somehow recognise that the humans bring food.
In the beginning, Pi was fairly safe as there was other food for the tiger, but once Richard Parker's food supply had run out, it was necessary for Pi to provide him food, just like at the zoo.
On Pi's part, it is his only way to survive under the conditions. One can say that once Richard Parker had eaten the other animals, the life boat became a mini zoo with the human being, Pi, providing for his needs.