In Lord of the Flies, the tropical setting significantly influences characterization.
Given the darkeness of the jungle/forest both literally and figuratively, we see Golding developing the evil of characters the further they proceed into the forest/jungle. When out in the sun and on the beach characters are at play, assemblies are held, responsibilty is set there in the light.
As Jack for example spends more and more time in the forest, his thirst for a kill grows. Although this original dream of a kill is for a pig so that he can participate in helping feed the children, when the boys pretend to have a "kill the pig" ceremony with a human (Robert) in chapter 5, this foreshadows that the eventual killing of a human could be possible. What seems to be a joke thoroughly scared Robert for a time. Later in the text, we see this dark side of humanity become reality.
Having the setting place children completely away from authority also plays an important role in the development of character. Had the children been around their teachers, parents, or even police officers, or adults of any kind, the story would not have travelled in the direction that it did. This loss of authority caused the children to revert to their most innate instincts of selfishness and disorder. We see this longing for boundaries through the character Piggy. Through Ralph, we see the celebration of a departure from adults, but as the book continues, Ralph being elected leader heaped responsibility on his shoulders. I bet he would have risked much for the opportunity to ask an adult for help. Through the littuns we see the fear they encounter because they are so used to having adults stifle or protect them from that which would scare them.
You can further read enotes anaylsis linked below that discusses the setting as an allusion to society.