Animals are consumers. Herbivores, which consume plant matter directly, are primary consumers. Secondary consumers, or primary carnivores, are those that devour primary consumers. Decomposers are life forms such as bacteria, fungi, and other microorganisms that break down the remains of other organisms, and thus return nutrients to the soil to be used by green plants. The sequence from green plant to secondary carnivore is called the food chain.
All habitats have many intricately interrelated food chains, forming a food web.
Deficiency in any one part of a habitat's ecosystem changes the entire system. If the deficiencies are too great, the entire ecosystem can collapse. In such an event, species would decline or disappear, and the ecosystem's diversity would be largely eliminated.