Question

A keystone species is the one which has
A. Small proportion of total biomass but has a huge impact on the community's organization and survival
B. A plenty of biomass but low impact on community organization.
C. A rare species with little impact on biomass and other species in the community
D. A dominant species which has a large proportion of biomass and which affects many other species.

Answer 1

Hint: Keystone species is a species which has larger effect on natural environment, where the concept of keystone species was introduced by Robert T Paine in the year 1969, and this keystone species are described as the one that play critical role in maintaining the structure of an ecological community, and affecting many other organisms in an ecosystem.

Complete answer:
Keystone species plays very important role in an ecosystem, in order to explain its importance, a small example that is, if there an arch which is made of stones, and among those stones, there is one which may be small or large, or bearing low pressure or total pressure, where if the stone is removed, whole arch is collapsed, similarly, irrespective of size of species, they are very important for the balance of ecosystem.
There is a dominance shift in the environment, if the keystone species are removed.
Keystone species play a very crucial role even if they make very small measurements of the biomass.
This concept of keystone is very popular in conservative biology.
Generally a keystone species is a predator, which means they kill the other organisms for their food, so this keystone species predates the herbivores, where these herbivores depend on many numbers of plants for their food, and this may result in elimination of dominant species, so the ecosystem alters dramatically.

So the correct option is A.

Note: To say simply if the predator’s numbers are low, and keystone predators can be even less abundant and still be effective, but without predators, the herbivores prey would explode in number, without the dominant plants and dramatically the character of the ecosystem.