Western harvest mouse (Reithrodontomys megalotis) COSEWIC assessment and update report: chapter 9

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Special Significance of the Species

In Canada, the western harvest mouse occurs only in restricted habitats of the intermontane grasslands of BC and the mixed grass prairie of southern Alberta. These two distinct populations are both at the northernmost limits of their North American range. Because of the selective pressures on individuals within populations at the periphery of a species distribution, marginal populations may be instrumental for maintaining the genetic diversity of a species (Scudder 1993). However, there are many instances where the opposite is true and swamping from core populations dis-allows local adaptation or clear differentiation.