Heterotrophs (other nourishing) are incapable of photosynthesis and depend on organic food derived from animals, plants or both. Consumers can be divided into two broad groups namely macro and micro consumers. (i) Macro consumers or phagotrophs feed on plants or animals or both and are categorised on the basis of their food'sources. Herbivores are primary consumers which feed mainly on plants e.g. cow, rabbit. Carnivores feed only on animals. Secondary consumers feed on primary consumers e.g. wolves. Carnivores which feed on secondary consumers are called tertiary consumers e.g. lions which can eat wolves. Organisms which consume both plants and animals are called omnivores e.g. men. (ii) Micro consumers - Saprotrophs (decomposers or osmotrophs) are chiefly bacteria and fungi which obtain energy and nutrients by decomposing dead organic substances (detritus) of plant and animal origin. Some of the products of decomposition such as inorganic nutrients released in the ecosystem are reused by producers and thus recycled. Earthworm and certain soil organisms such as nematodes, and arthropods are also detritus feeders and help in the decomposition of organic matter.