- Food Chains are found in two parts of an ecosystem. The “grazing” food chain includes the producers and consumers that cycle energy from living plants. The “detritus” food chain cycles energy from non-living remains of both plants and animals (also called detritus).
- The “grazing” food chain has a number of steps that start with the producers, or the plants, and flows through a series of levels of consumers. At each step only about 10% of the energy is passed up through the chain. The rest is passed back into the atmosphere as heat through breathing and decomposition.
- The “detritus” food chain is a system where the energy produced by the breakdown of dead plant and animal matter is cycled into the “grazing” food chain. Detritus is organic matter formed by decaying animal or plant tissue, or fecal matter. Detritus eaters (or detritivores) such as insects, worms and other small organisms feed on dead plants, waste products from animals and dead animals.
In nature, the food and feeding relationships of plants and animals are rarely as simple as the examples of food chains described above, because many animals eat more than one kind of food. On this account, different kinds of food chains overlap each other or intercross each other. The food chains do not operate in isolation. This network of food chains operating in nature in a particular area is called a food web. For example, grass is eaten by grasshoppers as well as by rabbits, deer or cattle, and each of these herbivores may be eaten by many carnivores, such as frog, snake, eagle or tigers depending upon their food habits.
Each link in a food chain is known as a trophic level. For example, in each food chain, plants always form the first trophic level. The plant eating animals called herbivores like insects, rodents, rabbits, deer, cattle, etc. form the second trophic level. The animals like frog, small fish, small birds which feed on the second trophic level organism form the third trophic level. These are eaten by still longer carnivores like lion or tiger, who constitute the fourth trophic level.