Rapoport's rule: time for an epitaph?

The christening of the decline in the geographic extent of species from high to low latitudes as Rapoport's rule was a bold step. Allowing for a variety of potentially significant complications to the interpretation of empirical studies, evidence that this is indeed a general pattern is, at the very least, equivocal. The present taxonomically and regionally biased set of studies lend support to the recent suggestion that the pattern is a local phenomenon being expressed primarily in the Palaearctic and Nearctic above latitudes of 40-50°N. Five hypotheses have been proposed to explain the generation of latitudinal declines in range size where they do occur, with the past heavy emphasis on a climatic variability mechanism being eroded. Evidence is accruing in support of more than one such mechanism. Whatever the generality of the `rule', it has undoubtedly served to stimulate a consideration of the role of spatial variation in range sizes in several areas of research in ecology and evolution.