and frogs. As a result, food chains become branched and interlinked at various stages leading to a weblike structure. This is called a food web.

Apart from the food chains pyramids are another type of representations which show flow of energy from one organism to another. You may have heard about pyramids of Egypt. The ecologists also used this idea of pyramid to show relationship among organisms in an existing food chain. In short we can say that graphic representation of the feeding level (tropic level) of an ecosystem in the shape of a pyramid is called “Ecological pyramid”. It was first introduced by a British ecologist Charles Elton in 1927. In the ecological pyramid the producers (first trophic level) are represented at the base; and other successive trophic levels (primary, secondary and tertiary consumers) are represented one above the other with top carnivores at the tip. There are three types of pyramids; pyramid of biomass, pyramid of number, pyramid of energy. In this chapter we will try to discuss about the pyramid of number biomass and energy.

Biologists are not only interested in studying the food relationships which exists between living things, but also in comparing the numbers of organisms at each link in the chain. Here is an example of food web to make estimates of the comparative numbers of organisms present at each stage of chain. The comparison needs to involve the use of such terms as most, many, several, few and scarce. Is there any relationship