Biodiversity is not uniformly distributed throughout the world. Polar regions have very little biodiversity whereas South America has the greatest biodiversity on the earth.
There are many hypothesis for higher biodiversity in tropics:
1. There are no unfavourable seasons in tropics. Continued favourable environmental condition has helped tropical organisms to flourish more.
2. There is more solar energy available in the tropics due to which productivity is higher and this contribute to greater diversity.
The tropical environment is older thus allowing more time for the evolution of greater number of plants and animals.