MORPHOMETRIC VARIATION IN KANGAROO RATS (GENUS DIPODOMYS) AND ITS RELATIONSHIP TO SELECTED ABIOTIC VARIABLES

Geographic patterns of morphometric variation, as represented by projections of samples on the first principal component, were obtained for 14 species of kangaroo rats (genus Dipodomys) by using principal components analysis. The amount of variation accounted for by the first principal component ranged in males from 37.5 (D. nelsoni) to 87.1% (D. californicus) with a mean of 61.2%. These values for females were from 51.1 (D. phillipsii) to 83.9% (D. californicus) with a mean of 65.3%. Characters that consistently accounted for the most variation for this component were total length of skull, basal length, greatest width of skull, and width of mastoid bullae. Values for the projections of the samples on principal component I (frequently considered a body-size index) were compared to values of latitude, and annual values and seasonal ranges of temperature, precipitation, and actual evapotranspiration by using Pearson's product-moment correlation analyses. Of these abiotic variables, annual temperature was considered a slightly more-appropriate predictor of size variation. Beyond a tendency for size to increase with decreasing annual temperature (in accordance with Bergmann's Rule), there was little general pattern of correlation between morphometric variation and these abiotic features. Had fewer species of kangaroo rats been examined, conclusions would have depended on the taxa analyzed. It appears that abiotic parameters may effect morphometric variation in some portions of the distribution of a species, but may be superseded by different factors in other parts of that taxon's range.