Steller’s sea cow is an example of:

The correct answer is Option (1) → Over-exploitation.

The four major causes of biodiversity loss are called ‘The Evil Quartet’: habitat loss and fragmentation, over-exploitation, alien species invasions and co-extinctions. Over-exploitation happens when human ‘need’ turns to ‘greed’ and a species is hunted or harvested faster than it can recover. Steller’s sea cow and the passenger pigeon were wiped out by overexploitation.

Option (1) Over-exploitation. — Correct. Steller’s sea cow was hunted to extinction, so it is the book’s example of over-exploitation.

Option (2) Alien species invasions. — Incorrect. Alien species invasions harm native species when outsiders turn invasive, as the Nile perch did to the cichlid fish of Lake Victoria.

Option (3) Co-extinctions. — Incorrect. Co-extinction is the loss of species tied to one that dies out, such as the parasites of an extinct host fish.

Option (4) Fragmentation. — Incorrect. Fragmentation breaks large habitats into small pieces. It hurts animals that need large territories, such as mammals and birds.

NCERT Extract:
Loss of Biodiversity – “… (ii) Over-exploitation: Humans have always depended on nature for food and shelter, but when ‘need’ turns to ‘greed’, it leads to over-exploitation of natural resources. Many species extinctions in the last 500 years (Steller’s sea cow, passenger pigeon) were due to overexploitation by humans.”