Question

(a) Draw a ‘pyramid of numbers’ of a situation where a large population of insects feeds upon a very big tree. The insects, in turn, are eaten by small birds which in turn are fed by big birds.
(b) Differentiate giving reasons, between the pyramid of the biomass of the above situation and the pyramid of numbers that you have drawn.

Answer 1

Hint: An ecological parameter like the biomass energy or a number of individuals present in various trophic levels of a food chain is represented by ecological pyramids. A trophic level has all the members of all species operating at the same level. Hence the trophic level is called the functional level.

(a)

1. A pyramid of numbers represents the number of individuals per unit area of various trophic areas where producers are kept at the base and the tip is occupied by top carnivores.
2. The pyramid of numbers is mostly upright. The members of successive higher trophic levels are higher than the previous one.
3. A higher trophic level has fewer individuals than that of the lower trophic levels. This is because the organisms of the lower level provide the organism of a higher level with food.
4. When food is transferred, only 10 percent of the food is consumed by the higher trophic level organisms.
5. However, a tree that is a large-sized producer can provide food to several herbivores including birds.

(b)

1. Pyramid of biomass represents the biomass present sequence-wise per unit area of different trophic levels. It has producers at the base while the top carnivores are at the top.
2. The pyramid of numbers is different from the pyramid of biomass in the above situation because in the pyramid of biomass energy is spent at every stage. Only the number is taken into consideration in the pyramid of numbers.
3. Producers have the maximum biomass. Herbivores, primary and secondary carnivores have less biomass.

Note: Some important points to remember are listed below:
Terrestrial habitats have upright biomass.
Inverted or spindle-shaped biomass can be seen in aquatic habitats.
Only the number is taken into consideration in the pyramid of numbers.