Thus, we have a complex network of interconnected food chains called a food web.

For example, a snake might feed on a mouse, a lizard, or a frog. In turn, snake might be eaten by a bird or a badger.

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Types of Food Chains

Food Chains are of Following Two Types:

(i) Grazing food chain:

The grassland and forest ecosystems follow this grazing food chain. Here producers get energy from the sun and are grasses or green plants. They are subsequently grazed by animals.

Examples (i) Grass -> Grass hopper -> Frog -> Snake -> Hawk (ii) Green plants -> Goat -> Wolf -> Lion

(ii) Detritus food chain:

The estuarine and mangrove leaf ecosystems follow this detritus food chain. In this chain, the dead animals and dead plants and fallen leaves are consumed by detrivores and their predators.

Examples (i) Dead plants Soil mites – Insects -> Lizards

(ii) Dead organic matter -> Bacteria -> Protozoa – Rotifiers

Flow of Energy in an Ecosystem:

I. Flow of energy in an ecosystem takes place through the food chain.

II. The main source of energy for most ecosystems is the sun. Solar energy is trapped by producers. They store it as carbohydrates, proteins and fats. When primary consumers eat the producers, the energy also moves up the trophic level. During this transfer about 90% of the energy is lost as unusable heat to the environment.

III. We have an upright pyramid of energy flow as we move up the trophic levels, the amount of useable energy available at each stage declines.

IV. The ecological pyramid is the graphical representation of the organism’s position in the food chain. The base of the pyramid consists of the food producer level and the successive levels make the tiers with the top carnivore or tertiary consumers forming the apex.

V. The size of each compartment in ecological pyramid represents the amount of organisms (or item) in each trophic level of a food chain. Trophos is a Greek word meaning nourishment.

VI. Suppose the producer has 10,000 units of energy. When primary consumers eat the producers, they receive only 1000 units, rest 9000 units are lost as heat. Similarly, the secondary and tertiary consumers gets only 100 and 10 unit. The loss at each stage is simply released as heat into the environment.

VII. The flow of energy through the various components of the ecosystem is unidirectional and continuous. Unlike the nutrients which move in a cyclic manner and are reused by the producers after flowing through the food chain, energy is not reused in the food chain. All organisms require energy for growth, maintenance, reproduction, locomotion, etc the flow of energy in an ecosystem follow the laws of thermodynamics.

First law of thermodynamics:

Energy cannot be created or destroyed, but can be converted from one form to another.

Second law of Thermodynamics:

Transformations of energy always result in some loss or dissipation of energy.