Which of the following groups is absolutely essential functional component of the ecosystem?

Name an organism found as secondary carnivore in an aquatic ecosystem.

$A$- Grasshopper is included in primary consumer.

$R$- Fishes and birds are included in top carnivore.

Energy flow and energy transformations in living systems strictly conform to the

Assertion : Biotic community has higher position than population in ecological hierarchy.
Reason : Population of similar individuals remains isolated in the community.