(N/A) Speciation is generally a function of time. Unlike temperate regions,which were subjected to frequent glaciations in the past,tropical latitudes have remained relatively undisturbed for millions of years and thus,had a long evolutionary time for species diversification.
Tropical environments,unlike temperate ones,are less seasonal,relatively more constant,and predictable. Such constant environments promote niche specialization and lead to a greater species diversity.
There is more solar energy available in the tropics,which contributes to higher productivity; this,in turn,might contribute indirectly to greater diversity.