The living organisms which cannot manufacture their own food using the solar energy like the green plants and get their nutrition by eating other organisms are known as consumers. Most of the consumers of the living world are animals, e.g. mynas eat the insects, lion eats the deer, tiger eats men etc. So Myna, lion and tiger are consumers. As the consumer depends upon other living organisms for food or nutrition they are called heterotrophic. There are three levels of consumer’s namely Primary consumer, Secondary consumer and Tertiary consumer.
(i) Primary consumer: Herbivores or Green plant eating animals are known as Primary consumers. Zooplankton. various types of insects, goats, cows etc dircetly denends on plants.
(ii) The secondary consumer: The animals which live on primary consumers are known as secondary consumers, e.g. frogs eat insects and tiger, jackal etc. eat herbivores animals.
(iii) Tertiary or highest consumer: Those who live on secondary consumer, are tertiary or highest consumers. e.g. vulture, falcon, crocodiles. sharks etc are, tertiary consumers because they live on secondary consumers. There are many animals which live on food of more than one level e.g. when the peacocks live on plants, they are primary consumers and when they eat small insects, they are tertiary consumers. These sorts of animals are known as omnivorous animals. Man also consumes foods of different levels of the food chain to stay alive.