What is the term used to describe the phenomenon where the extinction of one species leads to the extinction of another species associated with it in an obligatory way?

Co-extinction

The correct answer is Option (3) – Co-extinction

Co-extinctions: The term used to describe the phenomenon where the extinction of one species leads to the extinction of another species associated with it in an obligatory way is "Co-extinction." Co-extinction occurs when two or more species have a dependent relationship, and the extinction of one species directly or indirectly causes the extinction of the other species. When a host fish species becomes extinct, its unique assemblage of parasites also meets the same fate. Another example is the case of a co-evolved plant-pollinator mutualism where extinction of one invariably leads to the extinction of the other.

Habitat loss and fragmentation: This is the most important cause driving animals and plants to extinction. The most dramatic examples of habitat loss come from tropical rain forests. Once covering more than 14 per cent of the earth’s land surface, these rain forests now cover no more than 6 per cent. They are being destroyed fast.

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. 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. Other examples of invasive weed species like carrot grass (Parthenium), Lantana and water hyacinth (Eicchornia). The recent illegal introduction of the African catfish Clarias gariepinus for aquaculture purposes is posing a threat to the indigenous catfishes in our rivers.