Variation in Geographical Range Size Among Mammals of the Palearctic

Rapoport's rule, the tendency for species' geographical range sizes to increase from the equator to the poles, holds for Palearctic mammals under four methods of analysis, each of which makes different statistical assumptions. The climatic variability hypothesis for explaining Rapoport's rule is tested. In support of the hypothesis, annual temperature range is a good predictor of range size. However, latitude is an even better predictor of range size. Because meridians do not cause ecological patterns, some other factor, for which latitude is a surrogate measure, must also determine range size; habitat size may be one such factor.