Which one of the following factors is not responsible for greater biodiversity of tropical regions?
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → No glaciations in the past
Species richness is highest near the equator and falls towards the poles. This is the latitudinal gradient of biodiversity. Three main reasons are given for the richness of the tropics: time (the tropics stayed undisturbed for millions of years), a constant environment, and more solar energy.
(1) Remained relatively undisturbed for millions of years — A factor responsible for the greater biodiversity of tropical regions. Species form slowly. Temperate regions suffered frequent glaciations, but the tropics stayed undisturbed. So they had a long evolutionary time for species to diversify.
(2) Environments are less seasonal, relatively more constant and predictable — A factor responsible for the greater biodiversity of tropical regions. A steady environment lets species specialise in narrow niches. This leads to greater diversity.
(3) Presence of more solar energy — A factor responsible for the greater biodiversity of tropical regions. More sunlight means higher productivity, and higher productivity can support more species.
(4) No glaciations in the past — Not one of the separate factors listed for the greater biodiversity of tropical regions. Glaciation comes in only as a contrast. It explains why temperate regions were disturbed and the tropics were not. That idea is already stated in Option (1). It is not a separate third reason, so this is the option that does not belong to the list.
NCERT Extract:
Patterns of Biodiversity – “… 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.”