Genetic Variability Within and Among Populations of the Black‐tailed Prairie Dog

Genetic heterogeneity over short geographic distances has been observed for many populations of small mammals (house mice: Selander, 1970; deer mice: Wright, 1978; pocket gophers: Patton and Yang, 1977; Smith et al., 1978; Wright, 1978; Patton and Feder, 1981) as well as for large, highly mobile species such as the elephant (Osterhoff et al., 1974), moose (Ryman et al., 1977, 1980), red deer (Gyllensten et al., 1980), and white-tailed deer (Manlove et al., 1976; Chesser et al., 1982). For most studies of the genetic structure of populations the specific mechanisms of genetic differentiation have not been identified. To understand the causes of population subdivision more fully, comparison of genetic variability should be made among the breeding and/or social units, rather than arbitrarily selected samples. Allele frequency differences among observed social groups within populations have been documented for house mice (Selander, 1970), dark-eyed juncos (Baker and Fox, 1978), marmots (Schwartz and Armitage, 1980), and humans (Neel and Ward, 1972). The organization of populations into independent breeding units may have important effects on the shortterm evolution of populations (Wright, 1980) as well as on the maintenance of genetic polymorphisms (Chesser et al., 1980; Karlin and Campbell, 1980). The black-tailed prairie dog (Cynomys ludovicianus) is perhaps the most socially complex of any rodent species (King, 1955; Koford, 1958). Prairie dog populations are comprised of several small coteries (har-