Ralph leads by what he sees as the rule of law. He feels that the boys need to be organized, that they need to follow rules, many of them suggested by Piggy, who represents society and the rule of law and reason on the island. For example, Ralph suggests that they take turns talking and whoever is in possession of the conch has the right to talk and the others have to listen.
Jack, on the other hand, represents and epitomizes the fear of the unknown and the rule of instinct and power. He capitalizes on the boys desire for meat, their fear of the unknown, and their desire to hunt and assume a masculinity and ferocity that they did not know in their previous life as obedient schoolboys. He is always pushing to see who wants to go hunt, who wants to play violently, etc.