Biodiversity includes all the flora and fauna on Earth. All the varieties of organisms come under biodiversity.

The region near the middle of the Earth between the Tropic of Cancer and Tropic of Capricorn is considered as the tropic region. This region receives the most amount of solar energy which leads to better productivity and higher species diversity. Also, the seasonal variations in such regions are low and environment mainly remains the same supporting high species richness and promoting niche specialization. Species-area relationship show a rectangular hyperbolic function. With very few exceptions, tropics harbour more species than temperate or polar areas. A forest in a tropical region like Equador has up to ten as many species of amphibians as a forest of equal area in a temperate region like the midwest of the USA.

Temperate regions include the subtropics and polar circles. These regions faced glaciation during the ice age which was not observed in the tropic regions.

When the diversity in organisms at the species level is termed as species diversity. Species diversity decreases as we move towards the poles can be for various reasons as - temperature decreases and conditions become harsh, the amount of solar radiation decreases including intensity, reduction in resources and vegetation for survival.