Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R).
Assertion (A): In a coevolved plant-pollinator mutualism, extinction of one partner invariably leads to the extinction of the other.
Reason (R): Co-extinction is one of the four major causes of biodiversity loss described as ‘The Evil Quartet’.
In the light of the above statements, choose the most appropriate answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Both (A) and (R) are true but (R) is not the correct explanation of (A).
Assertion (A): In a coevolved plant-pollinator mutualism, extinction of one partner invariably leads to the extinction of the other. — True. A is about what happens to the partners in a plant-pollinator mutualism. NCERT gives this as an example of co-extinction.
Reason (R): Co-extinction is one of the four major causes of biodiversity loss described as ‘The Evil Quartet’. — True. R is about where co-extinction stands among the causes of biodiversity loss. The four causes are habitat loss and fragmentation, over-exploitation, alien species invasions and co-extinctions.
Why R does not explain A? R only puts co-extinction in a list of causes. It does not say why the loss of one partner takes the other with it. The reason lies in the partnership itself: a coevolved plant and its pollinator depend on each other in an obligatory way, so when one becomes extinct, the other cannot survive. So both statements are correct, but R is not the explanation of A.
NCERT Extract:
Loss of Biodiversity – “… Causes of biodiversity losses: The accelerated rates of species extinctions that the world is facing now are largely due to human activities. There are four major causes (‘The Evil Quartet’ is the sobriquet used to describe them).”
Loss of Biodiversity – “… (iv) Co-extinctions: When a species becomes extinct, the plant and animal species associated with it in an obligatory way also become extinct. When a host fish species becomes extinct, its unique assemblage of parasites also meets the same fate. Another example is the case of a coevolved plant-pollinator mutualism where extinction of one invariably leads to the extinction of the other.”