The Edge Effect in Population Genetics

Abstract

Many animal species have been observed in which populations living near the edge of the range differ from those more centrally placed. Sometimes different peripheral populations resemble each other more closely than they do the central ones. Such a distribution is likely to be due either to more rapid change in central than in peripheral localities, or vice versa. In discussion of particular instances each alternative possibility has its adherents. It is suggested in this paper that in two examples from the European fauna (bank voles of the genus Clethrionomys and the snail Cepaea nemoralis) the distinct edge populations are less likely to be relicts than recent developments. Consideration of the response of populations of different sizes and breeding structure to the environmental conditions in various parts of the range suggests that we shall not know whether this is usually so, or whether peripheral populations play an important part in evolution, until the effects of coadaptation and interpopulation migration are better understood.