Geographic Variation in Variability of Pemphigus Populicaulis

ability profiles is studied based on stem mother, alate and gall characters of the aphid Pem-phigus populicaulis. Significant differences among the coefficients of variation of the suite of characters in every locality were found by two methods—Bartlett's test for homogeneity of variances (using log-transformed data) and Friedman's nonparametric test for randomized blocks. Nine characters are highly variable and six are consistently low in variability. Coef-ficients of variation show significant heterogeneity among localities for every character by Bartlett's test, and for all but two characters using a modified Friedman's test. The variability profiles of the 66 localities were clustered into three groups based on both size and shape by the fc-means algorithm. A mixture of two types of profiles occurs throughout the middle latitudes of the study area, while the third type is found in its northern and southern regions. This geographic pattern may in part be due to the year of collection. Attempts to relate the magnitude of the coefficients of variation to several ecological indices were unsuccessful. [Variability, variability profiles, geographic variation, coefficients of variation, Pemphigus.] This study investigates whether rela-tive morphological variability varies geo-