when pi and Richard Parker arrived on the floating island, why did Richard Parker returned to the boat at night?

One night Pi finally decides to sleep out of the boat, and with his net makes a bed in one of the trees. While there, he sees all the meerkets suddenly desert their ponds and run to the forest, and all climb up into the trees. Pi enjoys sleeping with the meerkats, so he continues to do so, until the day he finds a tree at the center of the forest that appears to be the only tree to have fruit. When he tries to eat the fruit, he finds that each piece of fruit is actually layers and layers of leaves wrapped tightly around a human tooth; what's more, together the fruit form a full, perfect set of teeth. Pi’s curiosity gets the best of him, and he tries to plant his feet on the island by night. The soil burns him terribly, however. It turns out that the island is carnivorous: it emits acid at night that dissolves anything on its surface. Pi must leave his semi-paradise, and is utterly weary as a result. He turns wholly to God.