The ecological pyramid is a graphical representation to show the relationship between various organisms at various trophic levels in an ecosystem.
The concept of the ecological pyramid was first introduced by Charles Elton in 1927.
The base of a pyramid is broad and its apex is narrow. The shape is the same for the food or energy relationship between organisms at different tropic levels. The relationship between food and energy between organisms at various trophic levels is expressed in terms of number, biomass or energy.
The base of the pyramid represents producers (First tropic Level). The apex represents tertiary consumers (top-level consumers).
Usually, 3 Types of Pyramids are studied they are:
- Pyramid of Number
- Pyramid of Biomass
- Pyramid of Energy
Pyramid of Number
- Only three top carnivores could be supported in an ecosystem of nearly 6 Million plants.
Pyramid of Biomass
- In the Pyramid of Biomass, there is a sharp decrease in biomass at higher trophic levels.
Inverted Pyramid of Biomass
- In the inverted pyramid of biomass, a very small crop of phytoplankton supports large zooplankton.
Pyramid of Energy
- The primary producers utilize and convert only 1% of the energy in the sunlight into NPP.
Calculation of Energy Content
When calculating the energy content, numbers of biomass. One needs to include all the organisms at that particular tropic level. If we take only a few individuals at any tropic level or generalisation will not give current values.
The important thing is trophic level represents a functional level, not a species.
Species with multiple tropical levels
For example, Sparrow is a primary consumer, when it consumes fruits, peas etc. The same sparrow becomes a secondary consumer when it consumes insects and worms. Similarly, humans are part of multiple trophic levels.
The ecological pyramid is always upright
In most ecosystem, the Pyramids of Biomass, energy, and number is always upright. For example,
- Producers are more in number and biomass than the herbivores,
- Herbivores are more in number and biomass than carnivores.
But importantly, there are exceptions. Such as insects feeding on trees. The number of insects is very high.
Also, the pyramid of biomass in the sea is generally inverted. The biomass of fishes exceeds the phytoplankton.
Pyramid of Energy is always Upright
The pyramid of energy is always upright and it is never inverted. This is because the energy flows from a particular trophic level to the next trophic level. As a result, some energy is always lost as heat at every step.
Each bar in the energy pyramid indicates the amount of energy present at each trophic level at a given time or annually per unit area.
However, there are some limitations of ecological pyramids. As it does not take into account the same species belonging to two or more trophic levels.
Also, the ecological pyramid assumes a simple food chain that never exists in nature and it does not accommodate a food web.
Also, saprophytes are not given any place in ecological pyramids even though
they have an important role in the ecosystem.