Given below are two statements, one is labelled as Assertion (A) and the other as Reason (R).
Assertion (A) : Maximum number of the species of butterflies are found in tropical countries.
Reason (R) :

Question

Given below are two statements, one is labelled as Assertion (A) and the other as Reason (R).
Assertion (A) : Maximum number of the species of butterflies are found in tropical countries.
Reason (R) : Butterflies can not tolerate low temperatures.
Select the correct answer using the codes given below :
Codes :

UnlockIAS · Accepted Answer

Correct — A, both (A) and (R) are true and (R) is the correct explanation of (A). The Assertion states the standard pattern of biogeography: butterfly species richness rises steeply from the poles towards the equator, and the wet tropics — the Amazon basin, the Indo-Malayan region, tropical Africa — hold by far the greatest number of species. India, tropical and subtropical, counts its butterflies in four figures while a temperate country such as Britain counts its resident species in dozens. The Reason gives the biological cause the examiner wants: butterflies are ectothermic (cold-blooded) insects whose body temperature follows the surroundings. They cannot generate enough internal heat to stay active in the cold — a butterfly must first bask, spreading its wings to the sun, until its flight muscles reach roughly the low thirties in degrees Celsius before it can fly at all — and egg, larval and pupal development is likewise driven by warmth. Where it is warm and productive all year, more species can complete more generations and coexist; where winter shuts flight and growth down for months, far fewer can persist. Because the temperature dependence of butterflies is what produces the tropical concentration, (R) genuinely explains (A), and the answer is (a). One honest caveat for a careful student: 'cannot tolerate low temperatures' is best read as 'cannot remain active in the cold'. Some butterflies do live in cold places — the Apollo butterflies (Parnassius) fly at great heights in the Himalaya, and temperate species survive winter in diapause as eggs, larvae or pupae, or migrate away from it. Warmth is also not the only driver of tropical richness; the year-round abundance of host plants, greater habitat complexity and a long, climatically stable history all contribute. The exam's reasoning is sound as the main cause, not as the only one.

Why the other options are wrong — (b) The two statements are not merely both true — they are causally linked. Being ectothermic is exactly why butterflies are concentrated in warm regions, so the Reason does explain the Assertion.  (c) The Reason is not false. Butterflies are cold-blooded insects that cannot fly until their flight muscles are warmed, and their development slows or stops in the cold — the reason is a correct statement of insect physiology.  (d) The Assertion is well established. Species richness of butterflies, like that of most groups, peaks in the tropics — this is the latitudinal diversity gradient, one of the oldest documented patterns in ecology.

Concept: Two ideas meet in this question. The first is ectothermy: insects, and butterflies among them, do not maintain a constant internal temperature, so ambient warmth sets the pace of flight, feeding, mating and development. The second is the latitudinal diversity gradient — for almost every major group of organisms, the number of species increases from the poles towards the equator. For a temperature-dependent group like butterflies, the two ideas fit together neatly: a warm, frost-free, continuously productive environment lets many species breed through the year and coexist in a fine-grained mosaic of niches, while a temperate or polar environment permits only the few that can survive a long dead season.

State PCS 2019 Q98 — Environment & Ecology PYQ with Answer

State PCS 2019 Q98 — Environment & Ecology PYQ with Answer