Graduate Thesis Or Dissertation

A morphometric analysis of geographic variation within Sorex monticolus

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  • Shrews previously recognized as Sorex monticolus were classified into two species (one with 14 subspecies, the other monotypic) on the basis of a morphometric analysis of 3610 individuals from throughout their range. Sorex m. neomexicanus has been recognized previously as a subspecies of Sorex monticolus but is recognized herein as a distinct species. This taxon occurs in the Sacramento and Capitan mountains of New Mexico. This region possibly acted as a boreal-forest refugium for S. monticolus-type shrews during the Pleistocene glaciation, and during the warmer interglacial period, after the most recent glaciation, the valleys became too arid for survival and these shrews survived in forested, montane regions of New Mexico. These mountains are sufficiently isolated from other mountainous regions in the state to reduce or eliminate gene flow between these populations of shrews. S. monticolus as defined herein exhibits relatively little morphometric variation. Even among nominate races, the only obvious morphometric variation is a north-south cline in greatest length of skull. There is a general trend of increasing size from south to north. The southern subspecies restricted to isolated mountains (S. m. monticolus and S. m. parvidens) have the shortest skull lengths of all S. monticolus. The subspecies found in the northern coastal and insular areas of southeast Alaska and British Columbia (S. m. longicaudus, S. m. prevostensis, S. m. malitiosus, S. m. insularis, S. m. calvertensis, S. m. alascensis, and S. m. elassodon) have the longest skulls. S. m. setosus, S. m. isolatus, S. m. soperi, S. m. obscurus and S. m. shumaginensis all have skulls of intermediate length. Insular and coastal populations of S. monticolus have longer skulls than the S. monticolus that occupy the mainland. Shrews with long skulls that occur on the mainland (S. m. longicaudus and S. m. alascensis) also occur on some islands, and the mainland portion of their distributions are restricted to a narrow band along the coasts of Alaska and British Columbia. The southernmost subspecies of S. monticolus with short skulls are restricted to small montane islands. The morphometric variation among nominate races is sufficient to warrant continued separation at the subspecies level of all taxa except S. m. calvertensis and S. m. elassodon. Were it not for differences in pelage color, based on my morphometric analysis, S. m. calvertensis and S. m. elassodon should be synonomyzed.
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