Graduate Thesis Or Dissertation

 

A morphologic and morphometric analysis of the "Sorex vagrans species complex" in the Pacific Coast region Public Deposited

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  • Shrews of the "Sorex vagrans species complex" were classified into nine taxa on the basis of morphologic and morphometric analyses of 2,299 specimens from Washington, west of the Cascade Mountains in Oregon, and in the Coast Ranges of California. In Washington, Sorex monticolus setosus and S. m. obscurus occur west and east of the Cascade Mountains, respectively. Oregon specimens heretofore considered S. m. bairdii were shown to possess morphometric differences sufficient to indicate they were specifically distinct from S. monticolus in Washington. The Columbia River may have acted as a barrier that led to a speciation event separating bairdii and monticolus. Seven specimens from Oregon, referred to S. m. setosus, were collected within 27 km of a landslide that dammed the Columbia River about 740 years ago. The slide probably was responsible for introduction of the taxon into Oregon. Holotypes of S. yaquinae (= S. pacificus yaquinae) and S. pacificus appear morphologically identical (the latter is damaged), thus the taxa were synonomized; the latter species name has priority. These shrews occur in the Oregon Coast Range from Taft, Lincoln Co., to Coquille, Coos Co., eastward to H. J. Andrews Experimental Forest, Linn Co., southward in the Cascade Mountains to near the California border. Sorex pacificus (= S. E. yaguinae) is morphometrically distinct from bairdii with which it is sympatric in the northern portion of its geographic range. Also, it is morphometrically distinct from shrews heretofore considered S. p. sonomae and S. p. pacificus and sympatric in the southern portion of its range with shrews formerly assigned to the latter taxon. Geographic variation within sonomae and pacificus is sufficient to warrant application of distinct trinomials to both taxa. Within my study area, S. vagrans exhibits no discernable geographic subunits. For all taxa, except S. vagrans, I found a relationship between latitude and the size of the projection on the medial edge of the first upper incisors from largest in the north to no projection in the south. This relationship likely is related to substantial differences in temperature, precipitation, and associated environmental factors over the 1,250 km from northern Washington south to San Francisco Bay, California. The southward reduction and ultimate loss of the median tine combined with the progressive enlargement of several skull characters associated with greater masticatory ability strongly suggests a dietary function for the median tine. Thus, changes in food resources of shrews in a southward direction in relation to increasing aridity and high temperatures possibly was the selective force responsible for reduction or loss of tines in southern taxa.
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