Territoriality and male reproductive success in arctic ground squirrels

Although territorial defense is a common form of reproductive competition a mong male vertebrates, the exact reproductive consequences of this behavior are often poorly understood. To explore relationships between territoriali ty and reproductive success in a nongroup-living mammal, we quantified patt erns of space use, mating success, and fertilization success for males in a free-living population of arctic ground squirrels (Spermophilus parryii pl esius). Because litters of this species are sired almost exclusively by a f emale's first mate, we predicted that territory ownership would be associat ed with first access to estrous females. During the 2-week period when mati ng occur-red, each male in the study population attempted to defend a disti nct portion of the habitat, although the success of this defense varied amo ng individuals. Twenty-six of 28 females monitored mated with the male on w hose territory they resided. However, the majority of females observed thro ughout estrus (65%; n = 20) also mated with at least one other ale, indicat ing that territory ownership was not associated with, exclusive access to f emales. In contrast, territory oivnership was significantly associated with first access to estrous females; 20 (71.4%) of 28 females mated first with the male on whose territory they resided. In this regard, the behavior of S. parryii plesius parallels that of socially monogamous birds in which ter ritorial defense by males functions to deter extrapair copulations by femal es. Although territorial defense represents an important component of male reproductive success in arctic ground squirrels, other aspects of male beha vior (e.g., the ability to dominate agonistic interactions on the day of a female's estrus) are also critical. We suggest that future studies of verte brate mating systems will benefit by viewing such defense as only one of mu ltiple axes along which conspecific males compete for access to females.