One-dimensional analyses of Rapoport's rule reviewed through meta-analysis

Aim To analyse quantitatively the extent to which several methodological, geographical and taxonomic variables affect the magnitude of the tendency for the latitudinal ranges of species to increase with latitude (the Rapoport effect). Location Global. Methods A meta-analysis of 49 published studies was used to evaluate the effect of several methodological and biological moderator variables on the magnitude of the pattern. Results The method used to depict the latitudinal variation in range sizes is a strong moderator variable that accounts for differences in the magnitude of the pattern. In contrast, the extent of the study or the use of areal or linear estimations of range sizes does not affect the magnitude of the pattern. The effect of geography is more consistent than the effect of taxonomy in accounting for differences in the magnitude of the pattern. The Rapoport effect is indeed strong in Eurasia and North America. Weaker or non-significant latitudinal trends are found at the global scale, and in Australia, South America and the New World. There are no significant differences in the magnitude of the pattern between different habitats, however, the overall pattern is weaker in oceans than in terrestrial regions of the world. Main conclusions The Rapoport effect is indeed strong in continental landmasses of the Northern Hemisphere. The magnitude of the effect is primarily affected by methodological and biogeographical factors. Ecological and spatial scale effects seem to be less important. We suggest that not all methodological approaches may be equally useful for analysing the pattern.