Latitudinal biodiversity gradients at three levels: linking species richness, population richness, and genetic diversity

Review methods

Species and population richness are the number of different species or populations in an area, respectively. Population richness can be totalled across species, within a species or averaged across species. Genetic diversity within populations can be summed or averaged across all species in an area or be averaged across an individual species. Using these definitions, we apply historical, ecological and evolutionary frameworks of species richness gradients to formulate predictions for intraspecific diversity gradients.

Review conclusions

All frameworks suggest higher average population richness at high latitudes, but similar total population richness across latitudes. Predictions for genetic diversity patterns across species are not consistent across frameworks and latitudes.

New analysis methods

Species range size tends to increase with latitude, so we used empirical data from c. 900 vertebrate species to test hypotheses relating species range size...