UKPSC Prelims 2025 General Studies Paper-I · Question 33 of 149

Correct — C, 1 and 2 both.

Statement 1 is the standard position: habitat loss and fragmentation is the leading driver pushing animal and plant species towards extinction. Clearing land removes habitat outright, and slicing what remains into patches strands species that need large territories or that migrate.

Statement 2 is over-exploitation — harvesting, hunting and fishing faster than populations can replace themselves. Steller's sea cow and the passenger pigeon are the standard examples of species lost this way in recent centuries.

Statement 3 is the reverse of what happens. A species tied to another in an obligatory way — a host's specialised parasites, a plant's sole pollinator — tends to go out with it. So 1 and 2 stand, 3 falls, and the key is 1 and 2 both.

Carry away the word co-extinction: a loss can travel along obligatory partnerships, so an extinction need not stop at the species that died.

• (a)
  Only 3 — This keeps the one statement that is false and throws away the two that are true. As printed, line 3 says the species associated with an extinct species do not themselves die out, which inverts the co-extinction idea.

  'Only 3' would fit a stem whose first two lines named things that are not drivers of biodiversity loss, with line 3 stating co-extinction the right way round. Here the reverse holds — line 3 is the flipped one and lines 1 and 2 both stand.

• (b)
  Only 1 — Line 1 is correct, so this option starts well and then discards line 2. Over-exploitation by human activity is a driver of biodiversity loss in its own right, not a restatement of habitat loss in other words.

  'Only 1' answers the narrower question of which single cause is described as the most important — habitat loss and fragmentation. This stem instead asks which of the printed statements are correct, and two of the three are.

• (d)
  Only 2 — Line 2 is correct, but rejecting line 1 means denying that habitat loss and fragmentation is the leading driver of extinctions. The superlative in that line is how the cause is ordinarily described, so it is not an overclaim to be struck out.

  'Only 2' would fit a version of the stem whose first line named some other driver as the most important one, such as pollution or warming. As this paper prints it, line 1 names the cause that carries that description.

The drivers of biodiversity loss are conventionally grouped as four, often called the Evil Quartet: habitat loss and fragmentation, over-exploitation, alien species invasions, and co-extinctions.

The first is loss of place, the second loss through use, the third loss to a new competitor, predator or disease, and the fourth loss carried across a dependency — one species disappearing because the species it was bound to has gone.

• The four causes of biodiversity loss are usually grouped as habitat loss and fragmentation, over-exploitation, alien species invasions and co-extinctions.
• Habitat fragmentation particularly affects mammals and birds that need large territories, and animals with migratory habits, whose populations then decline.
• Amazon rainforest is being cleared for cultivating soyabean and for conversion to grassland for raising beef cattle.
• Steller's sea cow and the passenger pigeon are cited as species driven to extinction by human over-exploitation within the last 500 years.
• Co-extinction: when a host fish species is lost, the unique assemblage of parasites specialised on it is lost with it.
• An obligate plant–pollinator pair shows the same effect, the extinction of one leading to the extinction of the other.
• The Nile perch introduced into Lake Victoria is linked to the loss of more than 200 species of native cichlid fish.
• Water hyacinth, Lantana and Parthenium are alien plants that have spread through and damaged native habitats in India.

• Line 3 carries a negative — 'do not become extinct'. A true principle printed in reverse is a false statement, so check polarity before judging content.
• The superlative in line 1, 'the most important cause', reads like an overclaim, but habitat loss and fragmentation is the cause ordinarily described that way, so the superlative alone is not grounds to reject line 1.
• Line 2 is broadly worded, but a general statement can still be a correct statement.
• Co-extinction turns on an obligatory association. A species with several alternative partners is not bound to follow any one of them out.
• The options here are codes, not facts. Settle each numbered line on its own first, because one wrong verdict removes the right code.

• practice — not a real PYQ

  Which of the following is NOT one of the four causes of biodiversity loss grouped together as the 'Evil Quartet'?

  • (a)Habitat loss and fragmentation
  • (b)Over-exploitation
  • (c)Alien species invasions
  • (d)Genetic drift in small populations
  Answerd — Genetic drift is a population-genetics process and is not a member of this group of four; the fourth member is co-extinction.

  Habitat loss and fragmentation (a), over-exploitation (b) and alien species invasions (c) are the other three named causes, so each of them fails the 'NOT' test.

• practice — not a real PYQ

  The introduction of the Nile perch into Lake Victoria is associated with the loss of a large number of native species of:

  • (a)Cichlid fish
  • (b)Freshwater turtles
  • (c)Water lilies
  • (d)Freshwater dolphins
  Answera — The episode is described as the loss of an ecologically unique assemblage of more than 200 species of cichlid fish native to the lake.

  The account names fish, not reptiles, so (b) fails; it names a predatory fish acting on other fish, not aquatic plants, so (c) fails; and (d) names a group not involved in this case.

• practice — not a real PYQ

  Consider the following statements about co-extinction: 1. It occurs when a species obligatorily associated with another disappears along with it. 2. A host fish species going extinct can take with it the assemblage of parasites specialised on it. 3. It is grouped with habitat loss, over-exploitation and alien species invasion as a cause of biodiversity loss. Which of the statements given above are correct?

  • (a)1 and 2 only
  • (b)2 and 3 only
  • (c)1 and 3 only
  • (d)1, 2 and 3
  Answerd — All three hold. Statement 1 is the definition, statement 2 is the standard illustration of it, and statement 3 places co-extinction as the fourth member alongside the other three causes.

  Options a, b and c each discard one statement that is true, so each of them is incomplete rather than wrong in what it keeps.