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Population and Geographic Variation of Peromyscus leucopus in Relation to Climatic Factors

James G. Owen
Journal of Mammalogy
Vol. 70, No. 1 (Feb., 1989), pp. 98-109
DOI: 10.2307/1381673
Stable URL: http://www.jstor.org/stable/1381673
Page Count: 12
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Population and Geographic Variation of Peromyscus leucopus in Relation to Climatic Factors
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Abstract

Variation of nine cranial characters in the white-footed mouse, Peromyscus leucopus, from 38 localities in the state of Texas, was studied. Significant age effects were detected for each character, but no sexual dimorphism and no sex-by-age interaction. Mean locality scores on the first morphological principal component, a size vector, revealed a statewide trend for larger mice to occur in the Panhandle and Trans-Pecos and for smaller specimens to occur in southern and southeastern Texas. A projection of the locality centroids onto the first two morphological principal components did not exhibit a pattern that indicated subspecific differentiation. This interpretation was reinforced by the large overlap among 95% confidence ellipses for locality populations about their means and by chromosomal studies in the literature. Mantel's test indicated that populations morphologically more different also occupy geographic areas climatically more different. The first two climatic principal components, derived from four climatic variables that measure mean annual temperature, mean July and January temperature, and mean annual precipitation, were interpreted as vectors representing temperature and precipitation, respectively. A multiple-regression analysis of size against the first two climatic principal components indicated that trends in size of white-footed mice follow Bergmann's Rule. There were significant inverse correlations between the first climatic principal component and seasonality of temperature, and between the second climatic component and seasonality of precipitation. This indicates that the traditional interpretation of Bergmann's Rule as a thermoregulatory response to cooler climates is confounded with adaptations to increased seasonality. Size allometry in white-footed mice may be a morphological response to harsh periods of low resource availability in seasonal climates. Seed productivity, a primary source of food for P. leucopus in Texas, may be correlated positively with size, and serve as an adaptive basis for selection of larger mice, with higher nutritional needs, in areas of higher seed resource availability.

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