Define Latitudinal gradients

Latitudinal gradients: Species diversity generally decreases as we move away from the equator towards the poles. Tropics have more species than temperate or polar areas. Many hypotheses have been proposed by scientists to explain greater diversity in the tropics. They are as follows:

1. Speciation is generally a function of time. Temperate regions had been subjected to frequent glaciations in the past. But tropical latitudes have remained relatively undisturbed for millions of years. This allowed a long evolutionary time for species diversification in the tropics.
2. Tropical environments are less seasonal, relatively more constant and predictable. A constant environment promotes niche specialization, and leads to a greater species diversity.
3. More solar energy is available in the tropics. It contributes to higher productivity. It may have indirectly contributed to greater diversity in the tropics.