Food Chain in an Ecosystem

Food Chain in an Ecosystem:

In the ecosystem, green plants alone are able to trap in solar energy and convert it into chemical energy. The chemical energy is locked up in the various organic compounds, such as carbohydrates, fats and proteins present in the green plants. All trophic levels in ‘an ecosystem is connected by transfer of food or energy.

The transfer of energy from one trophic level, e.g., producers, to the next trophic level, e.g., consumers, is called food chain. Thus, a food chain may be defined as the transfer of energy and nutrients through a succession of organisms through repeated process of eating and being eaten.

Mainly, food chains are of two types:

(i) Grazing food chain and

(ii) Detritus food chain.

i. Grazing Food Chain:

The grazing food chain starts from green plants and goes from herbivores (primary consumers) to primary carnivores (secondary consumers) and then to secondary carnivores (tertiary consumers) and so on. Cattle grazing in grasslands, deer grazing in forest, and insects feeding on crops and trees, are most common biotic constituents of the grazing food chain.

Autotroph → Herbivore → Primary carnivore → Secondary carnivore, etc..

ii. Detritus Food Chain:

The dead organic remains including metabolic wastes and exudates derived from grazing food chain are generally called detritus. The energy contained in detritus is not lost in ecosystem as a whole; rather it serves as a source of energy for a group of organisms called detrivores that are separate from the grazing food chain.

The food chain so formed is called detritus food chain. This begins with dead organic matter and passes through detritus feeding organisms (detrivores) in soil to organisms feeding on detritus-feeders.

In some ecosystems more energy flows through the detritus food chain than through grazing food chain. In detritus food chain the energy flow remains as a continuous passage rather than as a step wise flow between discrete entities.

In detritus food chain, there are many organisms which include algae, fungi, bacteria, slime molds, actinomycetes, protozoa, etc. Detritus organisms ingest pieces of partially decomposed organic matter, digest them partially and after extracting some of the chemical energy in the food to run their metabolism excrete the remainder in the form of slightly simpler organic molecules.

The waste from one organism can be immediately utilised by a second which repeats the process. Gradually the complex organic molecules present in the organic wastes or dead tissues are broken down to much simpler compounds, sometimes to carbon dioxide and water, and whatever is left that is humus. In a normal environment the humus is quite stable and forms an essential part of the soil.