The three hypotheses to explain species richness in tropics are
(i) The constant environment in tropics promotes niche specialisation and increased species diversity.
(ii) There is longer exposure to solar radiation in the tropical regions that contributes directly to higher productivity and indirectly to greater species diversity.
(iii) There occurred no glaciation in tropical region and it remained undisturbed. Thus organisms living in tropics continued to flourish and evolved more species diversity.
