I used behavioral and biochemical data to examine the adaptive significance of intraspecific variation in the reproductive and dispersal strategies of male arctic ground squirrels (Spermophilus parryii plesius). The population studied was located in the Kluane Game Sanctuary, Yukon, Canada. Females in this population regularly mated with more than 1 male during a single period of sexual receptivity; electrophoretic paternity exclusion analyses indicated that litters were typically sired by a female's first mate. I found that male reproductive behavior varied as a function of mating order and, hence, the likelihood of siring young. Specifically, reproductive competition among males appeared to be most intense prior to a female's first copulation. Reproductive males defended territories during the period between the birth and weaning of young. Non-reproductive males that immigrated to the study site during this period established residence on burrow systems occupied by lactating females; changes in burrow ownership invariably resulted in the loss of those females' litters. Paternity exclusion analyses indicated that males were typically the sires of litters reared on their territories. Territory defense significantly increased juvenile survival by preventing burrow takeovers by immigrants. Reproductive males benefitted from territory defense by increasing the survival of probable offspring; I suggest that territory defense between the birth and weaning of young functioned as a form of paternal care. Although most males in the study population dispersed as juveniles, some males delayed dispersal until their yearling season. Whereas juvenile-dispersers were reproductively active as yearlings, yearling-dispersers did not reproduce until they were 2 years old. Yearling-dispersers were slow growing individuals whose body weights remained less than those of juvenile-dispersers until mid-way through their yearling season. Non-reproductive yearlings were implicated in burrow takeovers that resulted in litter loss. Preliminary data suggested that the lifetime reproductive success of yearling-dispersers was less than that of juvenile-dispersers. I argue that costs of dispersal are tolerable for large, but not small juveniles; as a result, small males are forced to remain in their natal areas and to forego reproduction as yearlings.Ph.D.Biological SciencesZoologyUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/128816/2/9208584.pd
