Statement I: When a species becomes extinct, the plant and animal species associated with it in an obligatory way also become extinct.
Statement II: When alien species are introduced, some of them turn invasive, and cause decline or extinction of indigenous species.
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Both statements I and II are correct.
These two statements describe two of the four major causes of biodiversity loss, the ‘Evil Quartet’.
Statement I: When a species becomes extinct, the plant and animal species associated with it in an obligatory way also become extinct. — True. This is co-extinction. For example, when a host fish dies out, the parasites that can live only on it are lost too.
Statement II: When alien species are introduced, some of them turn invasive, and cause decline or extinction of indigenous species. — True. This is alien species invasion. The Nile perch in Lake Victoria and weeds such as Parthenium and Lantana are examples.
NCERT Extract:
Loss of Biodiversity – “… (iii) Alien species invasions: When alien species are introduced unintentionally or deliberately for whatever purpose, some of them turn invasive, and cause decline or extinction of indigenous species. … (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.”