Holarctic Marmots as a factor of Biodiversity.
Rumiantsev V.Yu;, Nikol'skii A.A. & Brandler O.V. eds.,
Abstracts, 3d Conference on Marmots (Cheboksary, Russia, 25-30 August 1997),
Moscow ABF 1997, 216p. : 191.


SOCIALITY AND AVERAGE FITNESS IN YELLOW-BELLIED MARMOTS


O.A. Schwartz*, K.B. Armitage**

* Department of Biology, University of Northern Iowa
** Department of Systematics and Ecology, The University of Kansas, Lawrence, USA


Sociality in mammals occurs when the costs are less than the benefits; benefits may increase may increase direct (individual fitness) and/or indirect fitness. In a species where sociality varies, we here test the hypothesis that increased sociality leads to greater average fitness for the group. The yellow-bellied marmot (Marmota flaviventris) is a social rodent that inhabits the mountainous regions of the western United States. The resource needs of marmots are typically patchy in distribution, variable in quality, and occur in a continuum of sizes; the larger sites contain social groups. Female fitness may be enhanced by recruiting daughters to the natal site, thus forming mother-daughter matrilines that may persist for several generations before extinction. Nearly all yellow-bellied marmots in breeding units in the East River Valley of Gunnison County, Colorado have been live-trapped, permanently marked, and observed yearly from 1962 to 1993. We calculated net reproductive rate as a measures of fitness for 16 breeding units, and calculated correlations between it and the following measures of sociality in the unit: proportion of all age females recruited into the natal site per all age females present, proportion of adult females recruited into the natal site per all adult females, the mean number of matrilines, and mean number of adult females per matriline. The Ro was positively correlated with the mean number of females per matriline (r=0.76) and the percentages of all age (r=0.52) and adult (r=0.69) females who were resident in their natal colony. Degree of sociality (expressed as variation in the size of matrilines) in a breeding unit is likely a function of the surrounding habitat quality and the behavioral phenotypes of the individuals, but the result is increased fitness for the unit.


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