Biology · Biodiversity and Conservation · NEET
NCERT lists exactly three. (1) Time: tropics were relatively undisturbed for millions of years, so species had a long, uninterrupted evolutionary time to diversify, while temperate regions were repeatedly disturbed by glaciations. (2) Constancy: the tropical environment is less seasonal, more constant and predictable, which promotes niche specialisation and leads to greater species diversity. (3) Productivity: tropics receive more solar energy, which gives higher productivity, and this may indirectly contribute to greater diversity. A simple hook is TCP - Time, Constancy, Productivity.
Speciation (the making of new species) is a slow process that needs long, undisturbed periods. Temperate regions went through repeated glaciations in the past, which wiped out or disturbed species again and again. Tropical regions stayed relatively undisturbed for a very long geological time, so life there had far more time to keep forming new species. More time undisturbed means more speciation, hence more diversity.
A niche is the role and space a species uses in a habitat. Because tropical environments are less seasonal, constant and predictable, species can afford to specialise on a narrow food source or micro-habitat without the risk of harsh seasonal swings wiping them out. Many species can each occupy a narrow niche side by side. This packing of many specialised niches into one area means more species can coexist, so diversity is higher. Temperate species must be generalists to survive strong seasons, so fewer species fit.
No, and this is the common trap. NCERT says more solar energy in the tropics leads to higher productivity, and this in turn MIGHT contribute INDIRECTLY to greater diversity. The link is indirect, not direct. Solar energy raises productivity first; the effect on species number is a possible indirect consequence, not a proven direct cause. Use the exact words 'indirectly' and 'productivity' for NEET.
NCERT does not name a single scientist for the three hypotheses (Time, Constancy, Productivity) - it presents them as explanations proposed by ecologists in general. Do not confuse this with named scientists in the same chapter: Alexander von Humboldt gave the species-area relationship, Robert May gave the global species estimate, and David Tilman worked on diversity and ecosystem stability. The three tropical-diversity hypotheses have no single name attached in NCERT.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Use TCP: Time (more evolutionary time), Constancy (constant, less seasonal environment promoting niche specialisation), and Productivity (more solar energy, higher productivity, indirectly more diversity).
Temperate regions faced repeated glaciations in the geological past. These disturbances interrupted speciation again and again, so temperate species had less undisturbed evolutionary time than tropical species.
Indirect. NCERT states that more solar energy raises productivity, which in turn 'might contribute indirectly' to greater diversity. NEET often tests this word 'indirectly'.
NCERT says 'with very few exceptions' tropics harbour more species than temperate or polar areas. Species diversity generally decreases as we move from the equator towards the poles.
