Species diversity decreases as we move away from equator towards poles. What could be possible reasons? 

Following are the reasons for greater species diversity near equator than at the poles. 
Equator receives direct illumination and hence had experienced more or less uniform climatic conditions throughout the history of evolution. Stable conditions near equator has given rise to large number of species. When we consider about the temperate regions; the climatic conditions have changed dramatically in these regions. Many species which lived in these regions become extinct during dramatic climatic changes. Hence, we find a lower number of species in these regions. In polar regions due to extreme cold climatic condition and less availability of sunlight species diversity is very less.