One way to organise our information about the kinds of organisms in an ecosystem is by considering the movement of energy within the ecosystem, Energy is a common requirement of all organisms for maintaining themselves and for reproduction.
Solar energy is trapped by the green plant to manufacture carbohydrates, which form the essential food source sustaining all the organisms in the system. Solar energy is stored in plants as chemical energy, some of which is used for their biochemical and physiological processes.
The rest is stored and transferred from one organism to the other. Energy flow is considered as the movement of chemical energy among the populations of an ecosystem. As one organism (prey) is consumed by another organism, (predator) energy is transferred from the prey (food) to the other predator (consumer). This movement from one trophic level to another is never accomplished with 100% efficiency. There is always some loss of energy from level to level, since an organism, whether plant, animal or micro-organism (decomposer) uses some of its food energy for its own metabolism.
In a food chain, energy is transferred from green grass to hawk, (final consumer) with a progressive decrease in its amount. So also, the numbers of individuals in each trophic level decrease. This progressive loss of materials at each trophic level puts a natural limit on the total mass of living matter, that can exist at each level. When such a relationship is represented graphically by plotting the number of organisms, the biomass, and the energy content, each against a given period of time, with each horizontal bar representing a trophic level, the graph assumes a pyramid. Two common types of food pyramids in ecology are pyramids of numbers and pyramids of biomass. From the above, we have a pyramid of numbers, a pyramid of biomass and a pyramid of energy respectively.