Most groups of plants and animals have more species in the low latitudes than in the high latitudes. There are many possible explanations for this and many different opinions on the relative merits of those explanations. Solar energy is more abundant in the tropics and overall primary productivity is higher. Greater biomass in the tropical ecosystems (especially rain forest) leads to higher structural complexity and consequently greater opportunities for niche diversification. The climatic changes affecting the higher latitudes during the Pleistocene glaciations may not have caused such great disturbance in the tropics, though this is debatable. Evolutionary rates may be faster in the tropics, hence this may be the region in which many new taxa are generated, subsequently spreading to the higher latitudes.
Subjects: Ecology and Conservation.