Monitor lizards are important to food chains in their various terrestrial and aquatic (including marine) habitats, both as predator and prey. They consume a wide variety of invertebrates and vertebrates, including carrion, and even fruit in the case of some varanids. For humans, monitor lizards are important in various cultures for art, folklore, and a source of food, leather, and folk medicine. Thus, as with other taxa, varanids not only advance a function for the individual (survival, reproduction, self-maintenance of the species), but also provide a function for the whole (ecosystem, humans). This is the biological concept of bi-level functionality.