Which of these is not a reason accounting for greater biodiversity of tropics?

The correct option/answer is "large seasonal variations in environmental factors".

To understand why this option does not account for greater biodiversity in the tropics, let us analyze the factors that influence species richness and biodiversity in tropical regions compared to temperate regions:
1. Niche Specialization: Tropical environments are relatively constant, predictable, and stable. Such stable environments promote niche specialization and lead to a greater product of species diversity.
2. Solar Energy availability: There is more solar energy available in the tropics, which contributes to higher productivity; this in turn might contribute indirectly to greater diversity.
3. Time for species diversification: Speciation is generally a function of time. Unlike temperate regions which have been 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.
4. Seasonal Variations: Tropical environments, unlike temperate ones, are relatively constant and show less seasonal variation rather than large seasonal variations. Large seasonal variations, which are characteristic of temperate regions, make the environment harsh and unpredictable, thereby reducing species diversity. Therefore, "large seasonal variations in environmental factors" is not a reason for the greater biodiversity of the tropics; it is actually a characteristic of temperate regions which leads to lower biodiversity.