Patterns of Biodiversity

Patterns of Biodiversity

Biodiversity is not spread evenly across the globe — it shows a strong latitudinal pattern, with species richness increasing steadily from the poles toward the equator, so that tropical regions hold a disproportionately large share of the world's described species despite covering a comparatively small fraction of the Earth's land surface. Several factors are usually put forward to explain this pattern:

• Climatic stability over long timescales — tropical regions have experienced relatively stable climates over millions of years, without the repeated glaciations that swept temperate and polar latitudes, giving tropical lineages far longer, uninterrupted evolutionary time to diversify.
• Higher solar energy input and rainfall — the tropics receive more consistent, higher-intensity sunlight and, in most regions, greater and more evenly distributed rainfall through the year, supporting higher primary productivity, which in turn can support and sustain a larger number of species.
• Greater habitat and niche complexity — tropical ecosystems, especially rainforests and coral reefs, offer a much finer-grained mosaic of microhabitats and ecological niches (vertical stratification of forest canopy layers, for instance), allowing many more species to specialise and coexist without directly competing. …