Ecologists and evolutionary biologists have proposed various
hypotheses; some important ones are (a) speciation is generally a
function of time, unlike temperate regions 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; (b) 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, and (c) there is more solar energy
available in the tropics which contributes to higher productivity; this
in turn might contribute indirectly to greater diversity.