Q. Consider the following:

1. All alien species turn invasive and cause decline or extinction of indigenous species.
2. The Nile perch introduced in East Africa led to extinction of cichlid fish.
3. Parthenium, Lantana and Clarias gariepinus are examples of invasive weed species.

Which of the above is / are correct?
Answer: Only 2 is correct
Notes: Not all alien species become invasive; only some do. The Nile perch, introduced into Lake Victoria, led to extinction of cichlid fish, making statement 2 correct. Parthenium and Lantana are invasive weeds, but Clarias gariepinus (African catfish) is an invasive fish, not a weed species. Therefore, only statement 2 is correct.