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Variation in an isolated population of shrews of the Vagrans-Obscurus group Jackson, Mary Fairfield

Abstract

A study of shrews of the genus Sorex was undertaken at Point Grey, Vancouver, B.C. Trapping commenced in October 1949 and was continued except for brief periods until May 1951. A total of 1296 small mammals, including 670 shrews were obtained during the period. In the laboratory the animals were examined for parasites and condition of the reproductive system. Standard skull and body measurements, and counts of the number of caudal vertebrae were made on all shrews. Complete separation of the two species of shrews reported to be present on the campus ( Sorex vagrans and Sorex obscurus ) was found to be impossible on the basis of these measurements, even when sex and age of the animals were considered. An arbitrary separation of 95 percent of the material based on tail length and length of the maxillary tooth row was achieved. Differences in pelage were apparent, but not sufficient to separate the two species. Intergradation in all morphological features was taken as evidence that the two species are hybridizing to a considerable extent. Some evidence that the breakdown of mechanisms isolating the two populations has not been complete is presented. Hybridization in a local population such as the one studied was not considered a sufficient basis to change the specific status of S. vagrans and S. obscurus. Further study of these two species in other areas where they coexist in the same habitat is indicated.

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