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Geographic Variation and Sexual Dimorphism in Ord's Kangaroo Rat, Dipodomys ordii

Michael L. Kennedy and Gary D. Schnell
Journal of Mammalogy
Vol. 59, No. 1 (Feb., 1978), pp. 45-59
DOI: 10.2307/1379874
Stable URL: http://www.jstor.org/stable/1379874
Page Count: 15
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Geographic Variation and Sexual Dimorphism in Ord's Kangaroo Rat, Dipodomys ordii
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Abstract

Geographic variation was assessed in 4,335 male and 3,518 female specimens of Ord's kangaroo rat (Dipodomys ordii) from throughout the range of the species. A total of 16 skull measurements was analyzed and, of these, 11 showed significant sexual dimorphism. Greatest skull length, bullar-premaxillary length, and basal length showed the greatest relative differences between sexes. All characters showed significant interlocality variation in both sexes. Relative to the degree of intralocality variability, the third molar width showed the least interlocality variation; the three characters mentioned above plus greatest skull depth and upper diastemal length were the most variable between localities within each sex. Localities were projected onto three principal components based on correlations of characters. Component I (a size factor) showed that for both sexes the large individuals occur east of the western Cordillera, and smaller animals are found to the west in the United States and Mexico. Populations of the eastern and western parts of the range are linked by those that are morphologically intermediate. At least two complexes are formed in the western part of the range. Specimens from Padre and Mustang islands are separated from the others by component II, which has high loadings for greatest skull width, least interorbital width, least supraoccipital width, and greatest interparietal width. The third component has its highest correlation with third molar width, and the southernmost localities are large for this character. Patterns of interlocality heterogeneity are discussed in terms of sympatry with other Dipodomys species.

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