UPSC Prelims 2017 · Question 96 of 99

UPSC Prelims 2017 question on Butterfly Population Decline

Due to some reasons, if there is a huge fall in the population of butterflies, what could be its likely consequence/consequences?

1. Pollination of some plants could be adversely affected.

2. There could be a drastic increase in the fungal infections of some cultivated plants.

3. It could lead to a fall in the population of some species of wasps, spiders and birds.

Select the correct answer using the code given below:

  1. 1 only
  2. 2 and 3 only
  3. 1 and 3 only
  4. 1, 2 and 3
Show answer

Answer: C. 1 and 3 only

Verdict

The answer is 1 and 3 only. A collapse in butterfly numbers would affect pollination and reduce populations of their predators, but would not drive a rise in fungal infections.

Analysis

Statement 1 is CORRECT. Butterflies are pollinating insects and many flowering plants depend partly on them. Statement 3 is CORRECT. Butterflies and their larvae are a food source low in the food chain for wasps, spiders and birds, so a fall in their numbers propagates upward to the animals that feed on them. Statement 2 is INCORRECT. Butterflies play no role in suppressing fungal pathogens of cultivated plants, so their decline gives no reason to expect a drastic increase in fungal infection.

Source

The Hindu reporting on declining butterfly populations.

How to crack it

Trace the organism's actual ecological roles and accept only consequences that follow from one of them. A butterfly is a pollinator and a prey item, so pollination failure and predator decline follow directly, while fungal disease control is not a butterfly function at all. Asking what the organism does, and then testing each consequence against that list, prevents you from accepting plausible sounding ecological claims that have no mechanism behind them.

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