Question

(a) Compare the pyramids of energy, biomass and numbers.
(b) Write any two limitations of ecological pyramids. [5]

Answer 1

(a) Pyramid of energy: This type of pyramid shows energy relationship between organisms at different tropic levels. Each bar in the energy pyramid indicates the amount of energy present at each trophic level in a given time or annually per unit area. It is always upright.
Fig: Pyramid of energy.

Pyramid of biomass: This type of pyramid shows biomass relationship between organisms at different tropic levels. This pyramid can be upright as in the case of forest ecosystem or inverted as in case of sea ecosystem where phytoplanktons support fishes.
Fig: An upright pyramid of biomass

Pyramid of number: This type of pyramid shows relationship between number of organisms at different tropic levels. This pyramid can be upright as in the case of grassland ecosystem or inverted as in case of a tree ecosystem where number of insects feeding on a big tree is high.
Fig: Pyramid of numbers in a grassland ecosystem. [3]

(b) The limitations of ecological pyramids are

(i) It does not take into account the same species belonging to two or more trophic levels
(ii) It assumes a simple food chain, something that almost
never exists in nature
(iii) It does not accommodate a food web
(iv) Saprophytes are not given any place in ecological pyramids even though they play a vital role in the ecosystem.

Write any two for 2 marks.