Question

In a grassland ecosystem, if the number of primary producers is approximately 6 million plants, the number of the top carnivores, which may be supported by it may be ________ million.
(a) 3
(b) 30
(c) 6
(d) 60

Answer 1

Hint: If we arrange the organisms of grassland in the ecosystem pyramid, we find that the producer i.e. plants are the most in number and the other herbivores and carnivores are lesser in numbers than the producers. It is true for all ecosystems.

Complete step by step answer:
The number of carnivores will be 3 million.
According to the pyramidal concept, the number of organisms of different levels in an ecosystem always decreases as it goes to the upper level. Therefore, the number of carnivores living on plants has to be less than 6 million.

Additional Information: We know, the ecosystem is the interrelationship among the organisms in their physical environment. This consists of non-living factors like climate, soil, water, sunlight, etc, and living constituents. The living ones from different trophic levels in the ecosystem, the autotrophs make the producer level and the heterotrophs compose primary, secondary, tertiary, etc consumer levels depending on their food habits. The herbivores form the primary consumer level as they feed directly on plants and the carnivores from the other levels that feed on animals. These levels form the typical food chains of a region or ecosystem. For example, the grassland ecosystem consists of levels like this

Grass (producer) $\xrightarrow { } $ mouse (primary consumer) $\xrightarrow { } $ snake(secondary consumer) $\xrightarrow { } $ hawk (tertiary consumer) .
The whole trophic levels can be depicted by a pyramidic form where the top-level carnivores stay at the top and the producers stay at the wide base representing the most number of organisms. The number of organisms always decreases as we move up the pyramid.
So, the correct answer is ‘3 million’.

Note: There are several ecological pyramids that show energy, biomass, and numbers in different trophic levels. The number pyramid shows the graphical representation of the population at different trophic levels. In the question, we used the concept that the lowest level of the pyramid has the most population of the ecosystem and the lowest level consists of the producers always. Therefore, the number of carnivores has to be smaller than the population of plants.