Latitudinal gradients in species diversity and Rapoport's rule revisited: a review of recent work and what can parasites teach us about the causes ofthe gradients?

A review is given of recent work on latitudinal gradients in species divers ity and their explanations, including Rapoport's rule. Energy input. measur ed by temperature or potential evapotranspiration, correlates best with the gradients. However, such a correlation does not "explain" them. It merely suggests explanations. which may be either different ceilings to diversity set by different energy levels under equilibrium conditions. recent histori cal events, or a gradient in effective evolutionary time (determined by spe ed of evolution directly driven by temperature, and by relative constancy o f conditions over evolutionary time) under non-equilibrium conditions. Mari ne parasites are used to show that equilibrium conditions are the exception rather than the rule among animals. It is concluded that latitudinal gradi ents in species diversity result from a gradient in effective evolutionary time modulated by several other factors. Dispersal abilities of many marine invertebrates are likely to be greater at low than at high latitudes, sugg esting an opposite Rappoport effect.