Each plant, animal, and insect in the rainforest has a specific role. These organisms depend on one another for survival. This interdependence among the organisms, including man, has kept the rainforest in balance. As people settled and traveled to the islands, rainforests were replaced by agriculture, especially sugar, pineapple, and ranching. Other plants and animals also were introduced to the environment. Some of these plants and animals were invasive and became a threat to the balance of the rainforest.