Relative measures of geographic range size: Empirical comparisons

Many different measures of range size are used for both empirical and conservation purposes. The possible consequences of the particular methods used in determining observed patterns of results are seldom considered. Using species of butterflies and freshwater molluscs in Britain, we investigate the relationship between the range sizes measured by nine different methods and the sets of rare species they distinguish. A comparison of range sizes measured at different scales, Britain and Europe, is also made for the butterflies. We find that for many studies involving range size the various measures of range size are interchangeable. With respect to the identification of rare species the results are not as clear.