6. Ecological pyramids are pyramid-shaped diagrams representing quantitatively the numbers of organisms, energy relationships, and biomass of an ecosystem; numbers are high for the lowest trophic levels (plants) and low for the highest trophic level (carnivores). There are three types:

a. Number pyramid
It is easily understood that many grass plants are needed to feed fewer snails on which, in turn, even fewer chickens would be able to feed. This in turn requires only a few people to eat the chickens that ate the snails.


http://www.botany.uwc.ac.za/sci_Ed/grade10/ecology/trophics/troph.htm


b. Biomass pyramid

This pyramid indicates the total mass of the organisms in each trophic level. The size of the organism is over-emphasized and it can happen that the mass of level 2 is greater than that of level 1, because the productivity of level 1 is not taken into consideration. Thus an enormous mass of grass is required to support a smaller mass of buck, which in turn would support a smaller mass of lions.

http://www.botany.uwc.ac.za/sci_Ed/grade10/ecology/trophics/troph.htm

c. Energy pyramid
The Energy pyramid indicates the total amount of energy present in each trophic level. It also shows the loss of energy from one trophic level to the next. An energy pyramid shows clearly that the energy transfer from one trophic level to the next is accompanied by a decrease due to waste and the conversion of potential energy into kinetic energy and heat energy.



http://www.botany.uwc.ac.za/sci_Ed/grade10/ecology/trophics/troph.htm