MP Board · Class 12 · Biology · EcosystemDefine ecological pyramids. Describe the pyramids of number, energy, and biomass with suitable diagrams or descriptions, and mention their limitations.

Introduction to Ecological Pyramids\nThe base of an ecological pyramid represents the producers or the first trophic level, while the apex represents tertiary or top-level consumers. The relationship between different trophic levels in terms of energy, biomass, or number of organisms can be expressed graphically in the form of a pyramid, known as an ecological pyramid.

Types of Ecological Pyramids

1. Pyramid of Number:

   • It depicts the total number of individual organisms at each trophic level.
   • In most ecosystems (like grassland), the pyramid of number is upright because producers are maximum in number, and number decreases at higher trophic levels.
   • In a tree ecosystem, the pyramid is inverted because a single large tree supports numerous birds and parasites.

2. Pyramid of Biomass:

   • It represents the total dry weight of living matter at each trophic level.
   • In terrestrial ecosystems, the pyramid of biomass is upright as plant biomass is highest.
   • In aquatic ecosystems (like a pond), the pyramid of biomass is generally inverted because the biomass of phytoplankton (producers) is much less than that of zooplankton and fish (consumers).

3. Pyramid of Energy:

   • It shows the flow of energy from one trophic level to the next.
   • The pyramid of energy is always upright because energy flows unidirectionally and there is a loss of energy at each transfer according to the 10% law of Lindeman.

Limitations of Ecological Pyramids

• It does not take into account the same species belonging to two or more trophic levels simultaneously.
• It assumes a simple food chain, which almost never exists in nature; instead, a food web exists.
• Saprophytes/decomposers are not given any place in ecological pyramids, although they play a vital role in the ecosystem.