Question

Describe with examples of pyramids of number, and biomass.

Answer 1

There are three types of pyramids:

1. Pyramid of numbers
2. Pyramid of energy
3. Pyramid of biomass

• Pyramid of numbers:
  It is a graphical representation of the number of individuals present at each trophic level in the food chain of an ecosystem. The pyramid of numbers can be upright or inverted depending on the number of producers. For example, in a grassland ecosystem, the pyramid of numbers is upright. In this type of food chain, the number of producers (plants) is followed by the number of herbivores (mice), which in turn is followed by the number of secondary consumers (snakes) and tertiary carnivores (eagles). Hence, the number of individuals at the producer level will be the maximum, while the number of individuals present at top carnivores will be the least.

On the other hand, in a parasitic food chain, the pyramid of numbers is inverted. In this type of food chain, a single tree (producer) provides food to several fruit-eating birds, which in turn support several insect species.

• Pyramid of biomass
  A pyramid of biomass is a graphical representation of the total amount of living matter present at each trophic level of an ecosystem. It can be upright or inverted. In grasslands and forest ecosystems, the amount of biomass present at the producer level is higher than at the top carnivore level. In a pond ecosystem, the biomass of fish far exceeds the biomass of zooplankton (upon which they feed).

 

Answer 2

• Pyramid of numbers:

1. The relative number of individuals per unit area at different trophic levels constitutes the pyramid of numbers.
2. In a most well-balanced ecosystem, the pyramid of number is upright i.e. producers are more in number than herbivores, and herbivores are more in number than carnivores.

Upright pyramid of number

c. However, a pyramid of numbers can also be inverted in some cases.

For e.g., a tree ecosystem represents an inverted pyramid of numbers. If we plot the number of insects on a single tree, smaller birds feeding on insects, and parasites on those birds, we get an inverted pyramid.

• Pyramid of biomass:
  a. The amount of biomass per unit area at different trophic levels constitutes the pyramid of biomass.
  
  b. In a most well-balanced ecosystem, the pyramid of biomass is upright i.e. biomass of producers is more than that of herbivores, and biomass of herbivores is more than that of carnivores.

Upright pyramid of biomass

c. However, the pyramid of biomass can also be inverted in some cases. For e.g., the Oceanic ecosystem shows an inverted pyramid of biomass. In this case, the biomass of phytoplanktons (producer) is less than that of zooplanktons and fishes.