When you are speaking of the "events" in a novel, you are referring to plot elements: exposition, conflict, rising, climax, falling action, resolution. Let's take a look at each in turn.
The exposition of the story introduces the characters and the setting. This is in Part I of the novel. Readers learn about Pi growing up and his dad's zoo and his experiences with religion and his early journey on the Pacific Ocean. Even during the exposition, the theme seems to be "No small talk."
The element of plot that really starts the story going is the conflict. In this novel, the conflict is the very first line of Part II: "The ship sank." Here Pi's struggle begins. It is a struggle to survive.
Pi's entire struggle for survival on the life boat with Richard Parker is the rising action. This is entirely in Part II of the novel. There are many "events" during the rising action. A few that should stand out in a reader's mind are the disappearance of the first group of animals on the boat, the appearance of the flying fish, the appearance of the other castaway, the journey to the carnivorous island, and various storms and other hardships.
The very last part of Part II contains the climax of the novel: Richard Parker disappears unceremoniously.
Then, Richard Parker, companion of my torment, awful, fierce thing that kept me alive, moved forward and disappeared forever from my life.
The falling action begins with the first part of Part III. Pi recuperates from his injuries, he meets with the Japanese men, and tells them his "other" story.
The resolution involves the solving of the original problem. Readers learn that the important thing, and the "real" conflict was not that the ship sank, but that there are different thoughts about religion in the world. Pi's point becomes clear after the Japanese men choose "the one with the animals." Pi thanks them and says, "And so it goes with God."
Martel's Life of Pi is divided into three parts because each one represents a different episode in the boy's life. Within the first two, there are times when Pi shows curiosity in learning about the physical world and the spiritual world. He learns; he grows; and he becomes an expert about what he discovers.
The first part describes his life as a boy with his parents at the Zoo at Pondicherry. It also shows his keen sense of learning and obtaining knowledge in school, from the zoo, and about different religions. The second part, which is the biggest, of course, is his experience on the life boat--or is it? Here he demonstrates his wide knowledge about animals and their behavior, as well as what he learns in order to survive the Pacific Ocean. The things he learned in the first part of the book help him to survive the second part of the book. He applies all of the knowledge about animals, God, and himself to keep him alive for seven months!
The third part demonstrates the final stage of this bildungsroman. When Pi is reintroduced into society, he chooses how to view his experience on the ocean. He experiences so many horrifying situations because of the shipwreck that he not only has to survive physically, but he must now survive spiritually and mentally after such a traumatic experience. Without all three parts of the book, there wouldn't be a complete understanding of the significance of Pi's struggle on the ocean. For example, we wouldn't really understand where Pi's knowledge of animals or of God came from if we didn't have the first part to supplement the second part. More particularly, the third part of the book wouldn't be as shocking or as deeply penatrable if it weren't for the preceding two parts that build up to the amazing ending.