food chain

What is a food chain? 

The transfer of food energy from green plants (producers) through a series of organisms with repeated eating and being eaten is called a food chain.

Here grass is eaten by the grasshopper. Grasshopper is eaten by a frog. The frog is eaten by a snake and the snake is eaten by a hawk/eagle.

Each step in the food chain is called a trophic level. In the above example, grasses are first, and the eagle represents the fifth trophic level. Energy is passed up the food chain from one trophic level to the next. However, only about 10 percent of the total energy stored in organisms at one trophic level is actually transferred to organisms at the next trophic level. The rest of the energy is used for metabolic processes or lost to the environment as heat. 

Three important features that you can note in these chains are:

• Weaker organisms are attacked by stronger organisms.
• The number of organisms is reduced at each higher level but the size of organisms increases.
• The number of steps in a food chain is limited to 4-5.

A food chain consists of the following trophic levels:

1. Producers or Autotrophs: They are the producers of food for all other organisms of the ecosystem. They are largely green plants and convert inorganic material in the presence of solar energy by the process of photosynthesis into chemical energy (food). The total rate at which the radiant energy is stored by the process of photosynthesis in green plants is called Gross Primary Production. This is also known as total photosynthesis or total assimilation. From the gross primary productivity, one part is utilized by the plants for their own metabolism. The remaining amount is stored by the plant as Net Primary Production which is available to consumers.

2. Herbivores: The animals which eat the plants directly are called primary consumers or herbivores e.g. insects, birds, rodents, and ruminants.

3. Carnivores: They are secondary consumers if they feed on herbivores and tertiary consumers if they use carnivores as their food. e.g. frog, dog, cat, and tiger.

4. Omnivores: Animals that eat both plants and animals e.g. pigs, bears, and humans.

5. Decomposers: They take care of the dead remains of organisms at each trophic level and help in the recycling of nutrients e.g. bacteria and fungi.

Apart from these, there are special feeding groups. 

• Scavengers: These are the animals that feed on dead plants and animals. e.g. termites and beetles feed on decaying wood and many marine invertebrates. Vultures, gulls, and hyenas are other examples of scavengers.
• Omnivores: Omnivores consume both plants and animals as a source of their food e.g. human beings. Some omnivores like the red fox feed on berries small rodents as well as on dead animals. Thus it is a herbivore, carnivore, and also a scavenger.
• Parasites: They live and feed on/in other living organisms called the host. Parasites not only feed on their host but they also cause lethal or nonlethal diseases in it.

In nature, the food chains are not isolated sequences but they are interconnected with one another. A network of food chains that are interconnected at various trophic levels of the food chain to form a number of feeding connections is called a food web. One animal may be a member of several different food chains. Food webs are more realistic models of energy flow through an ecosystem. For example, a snake can feed on a frog or rat, or any other small rodent. A deer can be eaten by a lion or a hyena.