Local patterns of variation in the California scrub oak, Quercus Dumosa Nutt. (Fagaceae)

Four vegetative characters of leaves (length, width, petiole length and a number of teeth) and two reproductive characters (acorn length and acorn width) were measured in 58 individual plants located in Wildwood Park, a natural area in Thousand Oaks, California, U.S.A. The 58 plants were grouped into seven units, or subpopulations, separated from each other by at least 100 meters. The data was analyzed statistically to determine if these seven subpopulations are distinct interbreeding units. Hypotheses proposed to account for the variation were: genetic drift and founder effect, natural selection, hybridization, nonuniform dispersal of genotypes and environmental factors. The results of univariate and multivariate analysis suggested a pattern of relationships among the individuals and subpopulations related to their distribution. The results suggested that there are not seven units, but three. Each of these units is composed of two adjacent subpopulations. Evidence points to restriction of gene flow as a possible cause of the variation pattern. Other factors, such as environmental fluctuations, could not be excluded. Hybridization with other oak species, however, was rejected. The total variation among these plants was judged to be great, but within limits described by plant taxonomists.