The diagram below shows the tropic levels and relative sizes

The diagram below shows the tropic levels and relative sizes of productivity and biomass at four trophic levels. How can the size of the biomass in bottom trophic level be smaller than those of the tropic levels above?

Solution

Answer

Such an inverted pyramid of biomass is found in pond ecosystem. Pyramid of biomass takes into account the weight of a trophic level for a given unit area, e.g. the biomass of the producers, the biomass of the herbivores, the biomass of the carnivores, and so on.

Where the biomass of producers (phytoplanktons, Diatoms, Algae) is minimum- the first trophic level

The biomass of herbivores (insects, rotifers) is higher- the second trophic level

The biomass of carnivores (small fishes, minnows) is furthur higher- the third trophic level

Finally the top carnivore (large fishes) have highest biomass - the fourh trophic level.

the biomass of algae, diatoms is quite negligible as compared with that ofsmall herbivorous fish that feed on these producers. The biomass of top carnivorous fish living on small fishes is still greater.