FOOD CHAIN AND FOOD WEB

                                                                            FOOD CHAIN

            The transfer of food energy from the producers through a series of organisms (herbivores to carnivores and then to decomposers) with repeated eating and being eaten, is known as food chain.

            The solar energy is trapped in the ecosystem by the green plants and produce energy rich carbohydrates. These green plants are known as primary producers. The green plants are eaten by plant eaters (herbivores) also called primary consumers. Herbivores are in turn eaten by meat eaters (carnivores) also called secondary consumers. Secondary consumers in turn may be still eaten by other carnivores which are known as tertiary consumers. After decay of both plants and animals simpler compounds are being released into the atmosphere due to the activity of decomposers which are re-utilized by green plants.

            In nature, we generally distinguish two types of food chain – Gazing food chain and Detritus food chain.

            Example – A food chain in grassland ecosystem starts with grasses and goes through grasshoppers, the frogs, the snake and finally the hawks.

            Grasses ---------------- Frogs --------------- Snakes --------------- Hawks

            A detritus food chain starts with the dead plants and animals and goes through (fungi, bacteria, protozoa), (insect larvae, fishes, molluscs), (small fishes), (large fishes) and finally the )large fishes and birds).

            Fungi                           Insect larvae                                                     Large fishes

            Bacteria ---------------- Fishes ---------------- Small fishes ------------- Birds

            Protozoa                       Molluscs

FOOD WEB

            Food chains in ecosystems are found to be interconnected and usually form a complex network with several linkages and are known as food webs. Thus, “food web is a network of food chains where different types of organisms are connected at different trophic levels, so that there are a number of options of eating and being eaten at each trophic level.”

            For example – In an Antarctic ecosystem resemble the total ecosystem including the Antarctic sea and the continental land. The land does not show any higher life forms of plants. The only species are that of some algae, lichens and mosses. The animals include penguins and snow petrel which depend upon the Antarctic chain for their food energy.

            Food web gives greater stability of the ecosystem. In a linear food chain, if one species becomes extinct or one species suffers then the species in the subsequent trophic levels are also affected. In a food web, on the other hand, there are a number of options available at each trophic level. So if one species is affected, it does not affect other trophic levels so seriously.

            Consider the simple food chains of Arctic tundra ecosystem.

            Cladonia ------------ Reindeer ------------- Man

            Grass ---------------- Caribou ---------------Wolf

            If due to some stress, the population of reindeer of Caribou falls, it will leave little option for man or wolf to eat from the ecosystem. Had there been more biodiversity, it would have led to complex food web giving the ecosystem more stability.

            SIGNIFICANCE OF FOOD CHAINS AND WEBS

            1. Food chains and food webs play a very significant role in the ecosystem because the two most important functions of energy flow and nutrient cycling take place through them.

            2. The food chains also help in maintaining and regulating the population size of different animals and thus, help maintain the ecological balance.

            3. Food chains show unique property of biological magnification of some chemicals. There are several pesticides, heavy metals and other chemicals which are non-biodegradable in nature. Such chemicals are not decomposed by micro-organisms and they keep on passing from one trophic level to another. And, at each successive trophic level, they keep on increasing in concentration. This phenomenon is known as biomagnifications or biological magnification.

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