Graphic representation of the trophic structure and function at successive trophic levels of an ecosystem is called ecological pyramids. The concept of ecological pyramids was introduced by Charles Callou (1927). Thus they are also called as Eltonian pyramids.
There are three types: (1) pyramid of number (2) pyramid of biomass (3) pyramid of energy. Pyramid of number (Example)
A graphical representation of the number of organisms present at each successive trophic level in an ecosystem is called pyramids of number. There are three different shapes of pyramids upright, spindle and inverted.
There is a gradual decrease in the number of organisms in each trophic level from producers to primary consumers and then to secondary consumers, and finally to tertiary consumers. Therefore, pyramids of number in grassland and pond ecosystem are always upright.
In a forest ecosystem the pyramid of number is somewhat different in shape, it is because the base (`T_(1)`) of the pyramid occupies large sized trees (Producer) which are lesser in number. Herbivores (`T_(2)`) (Fruit eating birds, elephant, deer) occupying second trophic level, are more in number than the producers. In final trophic level (`T_(4)`), tertiary consumers (lion) are lesser in number than the secondary consumer (`T_(3)`) (fox and snake). Therefore, the pyramid of number in forest ecosystem looks spindle shaped.
The pyramid of number in a parasite ecosystem is always inverted, because it starts with a single tree. Therefore there is gradual increase in the number of organisms in successive tropic levels from producer to tertiary consumers.
