• Pyramids of numbers


• Pyramids of biomass


• Pyramids of energy

In a pyramid of biomass, it allows us to compare the mass of organisms present in each trophic level at a particular time. It is constructed based on the dry mass of organisms in each trophic level at any one time. This is called the standing mass of organisms.

In a pyramid of energy, the total energy in the various trophic levels of a food chain can be represented in the form of a pyramid. Unlike the pyramid of biomass, we need to determine the total energy content in each trophic level over a period of time(example: one year). This means that we have to take into consideration the rate at which organisms in each trophic level reproduce. The average energy content of each trophic level can then be calculated using special techniques. Knowing the energy content in each trophic level, we can construct a pyramid of energy. The pyramid of energy is thus constructed based on the total energy level in each trophic level over a certain period of time.

Most ecological pyramids are pyramid-shaped, but there are important exceptions. Example:

• tree--->aphid--->protozoa

In this case, the pyramid of numbers is inverted. The bottom of the pyramid is represented by only one tree. Many aphids are parasitic on the tree and many protozoa are parasitic on the aphids.

However, the pyramid of biomass remains broad and narrow at the apex. This is because one tree has a comparatively large biomass to support the other populations.

• Pyramids of biomass for rapidly reproducing organisms are also not pyramid-shaped. Since the pyramid of biomass is based on standing mass, it does not take into account the rate of reproduction of organisms. This is a disadvantage when considering organisms that reproduce rapidly.

phytoplankton--->zooplankton--->small fish--->large fish

Phytoplankton are microscopic plant-like organisms that can make food by photosynthesis. Zooplankton are microscopic primary consumers that feed on phytoplankton. For the food chain above, the pyramid may look like

The pyramid gives the impression that the biomass of phytoplankton is smaller than that of zooplankton, which is impossible. What happens is that the rate of reproductionof phytoplankton is fast enough to replace the organisms that were eaten by zooplankton.