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.

Both statements I and II are correct.

The correct answer is Opton (3) -Both statements I and II are correct.

Statement I: When a species becomes extinct, the plant and animal species associated with it in an obligatory way also become extinct.

This statement is true and refers to the concept of coextinction. Coextinction occurs when a species, known as the host species, becomes extinct, leading to the extinction of other species that are closely associated with it and depend on it for survival. These associated species are often specialized and have evolved unique adaptations to live in close association with the host species.

For example, some plant species rely on specific pollinators for reproduction. If the pollinator species becomes extinct, the plants will not be able to reproduce, and this can lead to the extinction of those plant species as well. Similarly, some species of animals depend on a particular food source or habitat provided by another species. If the host species goes extinct, these dependent species may also face extinction.

Statement II: When alien species are introduced, some of them turn invasive, and cause decline or extinction of indigenous species.

This statement is also true When alien species are introduced unintentionally or deliberately for whatever purpose, some of them turn invasive, and cause decline or extinction of indigenous species. The Nile perch introduced into Lake Victoria in east Africa led eventually to the extinction of an ecologically unique assemblage of more than 200 species of cichlid fish in the lake.