A host fish species in a lake becomes extinct, and the parasites that lived only on this fish also disappear. The loss of these parasites is an example of:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Co-extinction
When a species becomes extinct, the plant and animal species that depend on it in an obligatory way also become extinct. This is co-extinction. NCERT’s own example is a host fish: when it dies out, its unique assemblage of parasites cannot live on any other host and also meets the same fate.
Option (1) Over-exploitation — Incorrect. Over-exploitation is the loss of a species because humans take too much of it, as with Steller’s sea cow and the passenger pigeon. The parasites here were not harvested by anyone.
Option (2) Co-extinction — Correct. The parasites depended only on this host fish. Once the host was lost, they were lost with it, which is co-extinction.
Option (3) Alien species invasion — Incorrect. Alien species invasion is the harm done by a species brought in from outside, such as the Nile perch in Lake Victoria. No new species entered the lake in this case.
Option (4) Habitat loss and fragmentation — Incorrect. Habitat loss and fragmentation is the destruction or breaking up of the place where species live, as in tropical rain forests. Here the lake remains; only the host disappeared.
NCERT Extract:
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.”