Assertion (A): Tropical latitudes have greater species diversity than temperate regions.
Reason (R): Tropical latitudes were subjected to frequent glaciations in the past, which gave them a long evolutionary time for species diversification.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → (A) is true, but (R) is false.
Biodiversity is not spread evenly over the earth. In general, species diversity decreases as we move from the equator towards the poles. The tropics hold more species than temperate or polar areas, and ecologists have given three main hypotheses for this.
Assertion (A): Tropical latitudes have greater species diversity than temperate regions. — True. With very few exceptions, the tropics (23.5° N to 23.5° S) harbour more species than temperate regions. This is the latitudinal gradient in diversity.
Reason (R): Tropical latitudes were subjected to frequent glaciations in the past, which gave them a long evolutionary time for species diversification. — False. R puts the glaciations in the wrong place. It was the temperate regions that were subjected to frequent glaciations in the past. The tropical latitudes remained relatively undisturbed for millions of years. That long undisturbed time, not glaciation, gave the tropics more time for species diversification.
A is true and R is false.
NCERT Extract:
Patterns of Biodiversity – “… In general, species diversity decreases as we move away from the equator towards the poles. With very few exceptions, tropics (latitudinal range of 23.5° N to 23.5° S) harbour more species than temperate or polar areas. … Ecologists and evolutionary biologists have proposed various hypotheses; some important ones are (a) Speciation is generally a function of time, unlike temperate regions subjected to frequent glaciations in the past, tropical latitudes have remained relatively undisturbed for millions of years and thus, had a long evolutionary time for species diversification, (b) Tropical environments, unlike temperate ones, are less seasonal, relatively more constant and predictable. Such constant environments promote niche specialisation and lead to a greater species diversity and (c) There is more solar energy available in the tropics, which contributes to higher productivity; this in turn might contribute indirectly to greater diversity.”