Social enhancement of fitness in yellow-bellied marmots

摘要: The yellow-bellied marmot (Marmota flaviventris) is a social, ground-dwelling squirrel that lives either individually or in kin groups of from two to five adult females. Philopatry and daughter recruitment lead the formation persistence matrilines at habitat sites. By using 37 years demographic data for 12 sites, we could determine long-term trends effects group size on measures fitness, survivorship net reproductive rate, which otherwise are obscured by annual fluctuations these measures. Both number varied among sites rate matriline sizes. role social organization was explored further examining effect size, averaged over all fitness. For both relationship with curvilinear. Fitness increased increase then decreased largest groups. Decreased fitness four associated agonistic behavior, large 2-year-old females group, suppression. There no evidence acted their increasing indirect fitness; i.e., assisting relatives, but attempted direct Direct when mortality fission reduced surviving reproduction.