Distribution, abundance, size, and genetic variation of Peromyscus maniculatus on the Gulf Islands of British Columbia

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Abstract
On the Gulf Islands, Peromyscus maniculatus is found only on islands larger than 25 hectares (ha). Mandarte (5 ha) was an exception to this pattern but 15 other islands less than 25 ha had no deer mice. Tumbo (121 ha) was the only island larger than 25 ha without deer mice. Deer mice were abundant on the occupied islands and nearly all mice were adults in breeding condition. The average body weight of island mice was higher than for mainland deer mice.Genetic variation at the transferrin locus in P. maniculatus has also been examined. TfJ, the most common allele, had an average frequency of 0.74 on the islands, the same as the frequency of TfJ on the mainland. The variance of allele frequency was the same in mice on large and small islands. Physical proximity of islands was not related to allele frequency. Indeed, islands connected at low tide by sand beaches had widely different allele frequencies, and in one case a different set of alleles. These data quite clearly suggest a lack of genetic exchange between islands, even islands so close as to be connected at low tide. Little contemporary colonisation by P. maniculatus is evident. Extinction without subsequent colonisation appears to be the rule on these islands. The deer mice on these islands are not in a state of dynamic equilibrium.Dans les îles du Golfe, en Colombie Britannique, on rencontre des Peromyscus maniculatus seulement dans les îles pi us grandes que 25 hectares (ha), Mandarte (5 ha) constitue l'exception. mais 15 autres îles plus petites que 25 ha sont dépourvues de campagnols, Tumbo (121 ha) est la seule île plus grande que 25 ha à être dépourvue de campagnols. Dans les îles occupées, les campagnols sont présents en abondance et presque tous sont des adultes en état de reproductïon. Le poids moyen des campagnols insulaires est pins grand que celui des campagnols habitant le continent.

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