that are related to historical and evolutionary explanations for the increase of species diversity towards the equator. The historical perturbation hypothesis The historical perturbation hypothesis proposes the low species richness of higher latitudes is a consequence of an insufficient time period available for species to colonize or recolonize areas because of historical perturbations such as glaciation (Brown and Lomolino 1998, Gaston and Blackburn 2000). This hypothesis suggests that diversity in the temperate regions has not yet reached equilibrium and that the number of species in temperate areas will continue to increase until saturated (Clarke and Crame 2003). However, in the marine environment, where there is also a latitudinal diversity gradient, there is no evidence of a latitudinal gradient in perturbation. The evolutionary speed hypothesis The evolutionary speed hypothesis argues higher evolutionary rates due to shorter generation times in the tropics have caused higher speciation rates and thus increased diversity at low latitudes. Higher evolutionary rates in the tropics have been attributed to higher ambient temperatures, higher mutation rates, shorter generation time and/or faster physiological processes, and increased selection pressure from other species that are themselves evolving. Faster rates of microevolution in warm climates (i.e. low latitudes and altitudes) have been shown for plants, mammals, birds, fish and amphibians. Bumblebee species inhabiting lower, warmer elevations have faster rates of both nuclear and mitochondrial genome-wide evolution. Based on the expectation that faster rates of microevolution result in faster rates of speciation, these results suggest that faster evolutionary rates in warm climates almost certainly have a strong influence on the latitudinal diversity gradient. However, recent evidence from marine fish and flowering plants have shown that rates of speciation actually decrease from the poles towards the equator at a global scale. Understanding whether extinction rate varies with latitude will also be important to whether or not this hypothesis is supported. The hypothesis of effective evolutionary time The hypothesis of effective evolutionary time assumes that diversity is determined by the evolutionary time under which ecosystems have existed under relatively unchanged conditions, and by evolutionary speed directly determined by effects of environmental energy (temperature) on mutation rates, generation times, and speed of selection. It differs from most other hypotheses in not postulating an upper limit to species richness set by various abiotic and biotic factors, i.e., it is a nonequilibrium hypothesis assuming a largely non-saturated niche space. It does accept that many other factors may play