Compared the annual reproductive success (RS) of male and female founding immigrants (FIs) with that of subsequent immmigrants (SIs), and the latter with that of natal residents (NRs) in two recently established colonies of Spermophilus columbianus in SW Alberta. Among females, FIs had significantly more juveniles at their litter emergence, and more yearlings present to age of emigration annually than did SIs. Juvenile and yearling offspring of SI females suffered higher annual rates of disappearance (presumed mortality) over the active season than did those of FIs. The matrilines of FIs produced significantly more juveniles, more yearlings to time of emigration, and more daughters to reproductive maturity annually than did those of SI females. Male FIs had higher annual survival rates and had more female neighbours per year than did SI, which suggests that the former had higher annual RS. The higher annual RS of male and female FIs probably resulted mainly from their monopolization of the best resources and a lower risk of predation as a result of their more cenrtal position in the colony. Comparison of the annual RS of SIs and NRs showed that c70% adult males present in the colonies were SIs. These males were significantly more likely to hold territories and to do so for significantly longer periods than their NR counterparts. Conversely, SI females annually brought above ground significantly fewer juveniles and had significantly fewer yearling offspring present to time of emigration than did NR females. Results provide support for the hypothesis that females, apart from FIs, benefit from philopatry; males gain reproductive advantage through dispersal. -from Authors

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territoriality Canada Columbian ground squirrel ground squirrel reproductive success Spermophilus columbianus Alberta