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Food Chain and Food Web
It is a sequence of organisms through which energy is transferred in the form of food by the process of one organism consuming the other.
(i) Grass → Deer → Lion
(Producer) (Herbivore) (Carnivore)
(ii)Maize → Locust → lizard → Snake
(Producer) (Herbivore) (Carnivore) (Top carnivores)
• As the food chain goes on, the energy that is transferred to the next organism decreases.
1.0Trophic Levels
The distinct sequential steps in the food chain where transfer of energy occurs are referred to as trophic levels. e.g.,
(i) Green plants (producers) form the first trophic level, the producer level.
(ii) The plant eaters (herbivores), also called primary consumers, belong to second trophic level.
(iii) The primary consumer level and the flesh eaters (carnivores), also called secondary consumers, represent the third trophic level.
Plants → Men (Two trophic levels)
Plants → Goat → Men (Three trophic levels)
Plants → Mice → Snakes → Peacocks (Four trophic levels)
Plants → Insects → Frogs → Snakes → Eagles (Five trophic levels)
Plants → Grasshoppers → Frogs → Snakes → Hawks (Five trophic levels)
2.0Characteristics of Food Chain
1. A food chain involves a nutritive interaction between the living organisms (biotic components) of an ecosystem. In a food chain, there occurs repeated eating, i.e., each group eats the other group and subsequently is taken by some other group of organisms.
2. A food chain is always straight and proceeds in a progressive straight line.
3. Usually, there are 3 or 4 trophic levels in the food chain. In few chains, there may be maximum of 5 trophic levels.
4. Some organisms are omnivores. These occupy different trophic positions in different food chains.
5. At each transfer, generally 80-90% of energy is lost as heat in accordance with second law of thermodynamics.
3.0Types of Food Chains
There are two types of food chains.
Grazing Food Chains
Detritus Food Chain
• Detritivores obtain nutrients by consuming detritus (decomposing plant and animal waste as well as faeces) e.g., invertebrates like earthworm, insects such as mites, beetles, butterflies. They should be distinguished from other decomposers like bacteria and fungi which are unable to ingest discrete lumps of matter, but instead use saprotrophic feeding, in which they absorb nutrients through extracellular digestion.
• Kites and vultures feed on dead organisms and therefore, they act as scavengers.
4.0Significance of Food Chains
The significance of food chains can be seen with the help of following functions -
(i) It is a means of transfer of energy from one trophic level to another.
(ii) It provides information about the living components of an ecosystem.
(iii) A natural method of population control due to different nutritional habits.
(iv) It enables recycling of resources via decomposition.
5.0Food web
The interconnected food chains operating in an ecosystem which establish a network of relationships between various species is called a food web or the network of a large number of food chains existing in an ecosystem is called a food web.
Unlike food chain, food web are never straight.
Food webs help in checking the over population of species of organisms (both animals and plants).
A food web provides alternative pathways of food availability.
Differences Between Food Chain and Food Web
6.0Transfer of Energy in Ecosystem
Ten Percent law
It was put forth by Lindeman (1942). It is also termed as second law of thermodynamics or law of entropy. According to this law, transfer of energy from one trophic level to other trophic level is never 100 percent. It is so because most of energy gets lost as heat in the environment during each transfer. On an average, about 10% of energy is actually available to the next trophic level.