Pyramid of Energy - Ecological Pyramids

When we wish to compare the functional roles of the trophic levels in an ecosystem, an energy pyramid is probably the most informative. It overcomes some of the objections pertaining to the pyramid of numbers and biomass. An energy pyramid more accurately reflects the laws of thermo dynamics; with loss of energy being depicted at each transfer to another trophic level hence the pyramid is always upright. Energy pyramids in the case of aquatic ecosystem are also upright, even where the pyramid of biomass is inverted.

Figure:  Pyramid of energy.

In energy pyramids, a given trophic level always has smaller energy content than the trophic level immediately below it. This is due to the fact that some energy is always lost as heat in going from one trophic level to the next. Each bar in the pyramid indicates the amount of energy utilised at each trophic level in a given time, annually per unit area. The unit of measurement is kcal/m²/yr.