Latitudinal diversity gradients: equilibrium and nonequilibrium explanations

A central question in evolutionary ecology is: what are the reasons for differences in the abundance and diversity of organisms in different habitats and regions? Such differences are universal, i.e., it is highly unlikely that any two habitats will have the same number of species and organisms, and on a larger scale they are apparent between ecosystems and between latitudes, altitudes and different depths (in aquatic systems), as well as between different longitudes. By far the best-documented gradients are latitudinal ones, i.e., a very marked increase in diversity from high to low latitudes. An analysis of these gradients presents us with the opportunity to find a general explanation of the causes that determine diversity.