Read the passage and answer the question.
The base of a pyramid is broad and it narrows towards the apex. One gets a similar shape whether one expresses the food or energy relationship between organisms at different trophic levels. This relationship is expressed in terms of number, biomass or energy. The base of each pyramid represents the producers or the first trophic level, while the apex represents the tertiary or top level consumer. Any calculation of energy content, biomass or numbers has to include all organisms at that trophic level. No generalisation we make will be true if we take only a few individuals at any trophic level into account. Also, a given organism may occupy more than one trophic level simultaneously. One must remember that the trophic level represents a functional level, not a species as such. In most ecosystems, all the pyramids, of number, of energy and of biomass, are upright. There are, however, exceptions to this generalisation.
Read the passage and answer the question.
The base of a pyramid is broad and it narrows towards the apex. One gets a similar shape whether one expresses the food or energy relationship between organisms at different trophic levels. This relationship is expressed in terms of number, biomass or energy. The base of each pyramid represents the producers or the first trophic level, while the apex represents the tertiary or top level consumer. Any calculation of energy content, biomass or numbers has to include all organisms at that trophic level. No generalisation we make will be true if we take only a few individuals at any trophic level into account. Also, a given organism may occupy more than one trophic level simultaneously. One must remember that the trophic level represents a functional level, not a species as such. In most ecosystems, all the pyramids, of number, of energy and of biomass, are upright. There are, however, exceptions to this generalisation.
In an ecosystem, a sparrow eats seeds and fruits and also eats insects and worms. Using the idea given in the passage, the sparrow is placed at:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → The second and the third trophic levels at the same time
A trophic level is a functional level, not a species as such. One species can therefore work at two levels at the same time, depending on what it is eating. Producers are at the first level, herbivores (primary consumers) at the second and carnivores (secondary consumers) at the third.
Option (1) The second trophic level only, as a primary consumer — Incorrect. Eating seeds and fruits does make the sparrow a primary consumer. But it also eats insects and worms, which makes it a secondary consumer at the third level too.
Option (2) The second and the third trophic levels at the same time — Correct. On seeds and fruits it is a primary consumer (second level); on insects and worms it is a secondary consumer (third level). Both roles run side by side.
Option (3) The third trophic level only, as a secondary consumer — Incorrect. This leaves out the plant food. A sparrow eating seeds and fruits feeds directly on producers, so it also sits at the second level.
Option (4) The third and the fourth trophic levels at the same time — Incorrect. Eating insects and worms makes the sparrow a secondary consumer, which is the third level. To reach the fourth level it would have to feed on secondary consumers, and it would still be at the second level when it eats seeds.
NCERT Extract:
Energy Flow – “… Based on the source of their nutrition or food, organisms occupy a specific place in the food chain that is known as their trophic level. Producers belong to the first trophic level, herbivores (primary consumer) to the second and carnivores (secondary consumer) to the third (Figure 12.2).”
Ecological Pyramids – “… Also a given organism may occupy more than one trophic level simultaneously. One must remember that the trophic level represents a functional level, not a species as such. A given species may occupy more than one trophic level in the same ecosystem at the same time; for example, a sparrow is a primary consumer when it eats seeds, fruits, peas, and a secondary consumer when it eats insects and worms.”
Figure 12.2 Diagrammatic representation of trophic levels in an ecosystem