What kind of relationships can develop between plants and animals?

Basically, plants are food for animals, or material for construction, or are used as a shelter, this is their kind of relationship. Also, plants are often used by animals for treatment, animals unmistakably choose the right leaves, or roots that can help them get rid of ailments. Of course, among the flora, there are also some kind of predators capable of eating animal meat, or more often insects. Most of these plants grow in tropical forests.