Explanation:

Pyramid of numbers

Pyramid of numbers represents the total number of individuals of different species(population) at each trophic level.

• Depending upon the size, the pyramid of numbers may not always be upright, and may even be completely inverted.

• It is very difficult to count all the organisms, in a pyramid of numbers and so the pyramid of number does not completely define the trophic structure for an ecosystem.

Pyramid of numbers – upright

• In this pyramid, the number of individuals is decreased from lower level to higher trophic level. The grasses occupy the lowest trophic level (base) because of their abundance. • The next higher trophic level is primary consumer – herbivore (example – grasshopper).

• The individual number of grasshopper is less than that of grass. The next energy level is primary carnivore (example – rat).

• The number of rats are less than grasshopper, because, they feed on grasshopper. The next higher trophic level is secondary carnivore (example – snakes). They feed on rats.

• The next higher trophic level is the top carnivore. (Ex: Hawk).

• With each higher trophic level, the number of individual decreases. Pyramid of numbers – inverted

• In this pyramid, the number of individuals is increased from lower level to higher trophic level. E.g. Tree ecosystem.

Pyramid of Biomass

Pyramid of biomass is usually determined by collecting all organisms occupying each trophic level separately and measuring their dry weight. This overcomes the size difference problem because all kinds of organisms at a trophic level are weighed. Biomass is measured in g/m2

• The biomass of a species is expressed in terms of fresh or dry weight. Measurement of biomass in terms of dry weight is more accurate.

• Each trophic level has a certain mass of living material at a particular time called as the standing crop.

• The standing crop is measured as the mass of living organisms (biomass) or the number in a unit area.