AIPMT Biology Aspirants, read out the next AIPMT Biology Study material/ Notes, free ONLINE of Ecological Pyramids, important for AIPMT Biology.

We all are aware of the shape of a pyramid. The base of a pyramid is broad and it narrows down at the apex.

We got similar shapes like pyramid when we express food or energy relationship between organisms at different trophic levels. These, relationships are expressed in terms of Number, Biomass or Energy.

• Base of each pyramid represents Primary Producers (PP) or the first trophic level. Following the sequence from primary producer to primary consumer (PC) then secondary consumer (SC), apex represents tertiary or top level consumer (TC).
• The three ecological pyramids that are usually studied are

(a) Pyramid of Number

Pyramid of Number in Grassland Ecosystem

Only three top-carnivores are supported in an ecosystem based on production of nearly 6 millions plants.

(b) Pyramid of Biomass

Pyramid of Biomass

It shows a sharp decrease in biomass at higher trophic levels, in contrast to primary producers.

(c) Pyramid of Energy

Pyramid of Energy

• Pyramid of energy is always upright, can never be inverted, because when energy flows from a particular trophic level to the next trophic level, some energy is always lost as heat at each step.

• In most ecosystems, all the pyramids, of number, of energy and biomass are upright, i.e., producers are more in number and biomass than the herbivores, and herbivores are more in number and biomass than the carnivores. Also energy at a lower trophic level is always more than at a higher level.
• Pyramid of biomass in sea is generally inverted because the biomass of fishes far exceeds that of phytoplankton. Small standing crop of phytoplankton (PP) supports large standing crop of zooplankton (PC).

Inverted Pyramid of Biomass in Aquatic Ecosystem

• Trophic level in pyramids represents a functional level, not a species.
• Ecological pyramids always made for a simple food chain, which almost never exists in nature; it does not accommodate a food web.
• Even though saprophytes play a vital role in the ecosystem, they are not given any place in ecological pyramids.