Within-population craniometric variability of insular populations of deer mice, Peromyscus maniculatus, elucidated by landscape configuration

Within-population genetic variability of twelve insular and four mainland p opulations of deer mice (Peromyscus maniculatus) was assessed using craniom etric characters. and compared to results previously obtained from RAPD dat a. An index of Craniometric Variance (CVar) was computed from pairwise dist ances among all specimens. Variations in CVar measures were then compared t o landscape variables using a linear regression approach. Our results sugge st that CVar decreases in presence of large number of a competitive species (the boreal redback vole. Clethrionomys gapperi; r = -0.527. p < 0.037) in deer mouse populations. Island remoteness (r = -0.251, p <0.220) and the g eometry of the bank opposite to each island (r = -0.459, p < 0.067) were ma rginally correlated with CVar, but the linear combination of these two vari ables. forming a composite isolation index. represented the major factor ex plaining the observed CVar (r = -0.648. p < 0.011). Using a multiple regres sion model. 76.3% of the C Var was explained by a combination of this isola tion index and the competitors' abundance. These results suggest that takin g into account landscape barriers as well as the dispersal behavior of smal l mammals might provide sounder ecological variables than geographical dist ances alone for predicting within-population genetic variability in a netwo rk of habitat patches.