Tropical regions account for greater biological diversity because of…

The correct answer is Option (2) → Lower predation due to diversity of food availability

Species diversity is highest near the equator and falls towards the poles; this is the latitudinal gradient. Ecologists explain it by three hypotheses.

Option (1) Higher productivity due to more availability of solar energy — A reason for greater diversity in the tropics. More solar energy gives higher productivity, which can support more species.

Option (2) Lower predation due to diversity of food availability — Not a reason for greater diversity in the tropics. Predation is not among the three hypotheses. Predation does not lower diversity either: predators help to maintain species diversity by reducing competition among prey species.

Option (3) Tropics are less seasonal and relatively more constant and predictable — A reason for greater diversity in the tropics. A steady environment allows niche specialisation, so many species can live side by side.

Option (4) These latitudes are relatively undisturbed for many years leads to long evolutionary time for diversification — A reason for greater diversity in the tropics. Speciation is a function of time. The tropics escaped the glaciations of the temperate regions and had more time to form species.

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.”
Population Interactions – “… Predators also help in maintaining species diversity in a community, by reducing the intensity of competition among competing prey species.”