Consumers
Animals are wholly dependent on plants for their energy source. Animals are called "heterotrophs" (Greek: "other eaters") or "consumers".

Types of consumers (heterotrophs)
Consumers can be further grouped depending on what they eat.

• Herbivores eat only plant foods. For example, cows and kangaroos eat grass, caterpillars eat leaves, parrots and mice eat seeds and possums eat fruit or nectar. To chew and digest these cellulose-rich foods, herbivores have various specialised structures, such as grinding teeth and multiple stomachs with cellulose digesting bacteria in them.
  
  
• Carnivores eat only other animals for food. For example, cats eat mice, frogs eat insects, lions eat deer, and so on. Carnivores require sharp tearing teeth to rip through flesh, and have relatively simpler digestive systems because animal meat is easier to break down than cellulose.
  
  
• Omnivores can eat either plants or animals as food, but the cellulose from the plants is usually passed out undigested with the faeces. Being able to eat a range of foods makes an animal less dependent on any one food source, which aids survival.
  
  Humans are omnivores
  
  

• Scavengers are consumers that only feed on the bodies of dead organisms, e.g. ravens and Tasmanian Devils.
  

• Parasites are consumers which obtain food from a host animal or plant, but without killing it in the short term, e.g. tapeworms in a dog's intestine.

• Decomposers are tiny organisms which feed on dead organisms or waste matter and assist in the process of decay, e.g. bacteria, fungi and slaters.