Definition of Ecological Pyramid
Ecological Pyramid is a graphic representation of the relationship between organisms at various trophic levels in a food chain. The basis of an ecological pyramid is the biomass, energy, and number. Just as the name suggests ecological pyramids are in the shape of a pyramid. The concept was first introduced by Charles Elton, the Pioneer British Ecologist.
The bottom of an ecological pyramid is the broadest and is occupied the producers, which form the first trophic level. Producers are at the lowest level. Just as in a food chain, the producers are consumed by the primary consumers, in an ecological pyramid; the next level is occupied by the primary consumers. The next level of the pyramid is occupied by the secondary consumers and the last, by the tertiary consumers.
Types of Ecological Pyramids
- Pyramid of Numbers: This shows the number of organisms in each trophic level without any consideration for their size. This type of pyramid can be convenient, as counting is often a simple task and can be done over the years to observe the changes in a particular ecosystem. However, some types of organisms are difficult to count, especially when it comes to some juvenile forms. Unit: number of organisms.
- Pyramid of Energy: This is an upright pyramid that represents the flow of energy from the producers to the final consumers.
- Pyramid of Biomass: This indicates the total mass of organisms at each trophic level. Usually, this type of pyramid is largest at the bottom and gets smaller going up, but exceptions do exist. The biomass of one trophic level is calculated by multiplying the number of individuals in the trophic level by the average mass of one individual in a particular area. This type of ecological pyramid solves some problems of the pyramid of numbers, as it shows a more accurate representation of the amount of energy contained in each trophic level, but it has its own limitations. Ex:- The time of year when the data are gathered is very important, since different species have different breeding seasons. Also, since it’s usually impossible to measure the mass of every single organism, only a sample is taken, possibly leading to inaccuracies. Unit: g m-2 or Kg m-2.
All ecological pyramids are upright, except in certain cases. Ex: In a detritus food chain, the pyramid of numbers is not upright because many organisms feed on one dead plant or animal. The pyramid of biomass in an ocean is also inverted. But a point of note is that the pyramid of energy is always upright as the flow of energy is unidirectional.