PARENT SESSION

LIMITED DENSITY-DEPENDENCE IN YELLOW-BELLIED MARMOTS. Orlando A. Schwartz¹ and Kenneth B. Armitage². ¹ Department of Biology, University of Northern Iowa, Cedar Falls, IA, USA; ² Department of Ecology and Evolutionary Biology, University of Kansas, Lawrence, KS, USA.

ABSTRACT- Multiple lines of evidence have shown that population regulation of yellow-bellied marmots is extrinsic and largely density-independent. Our study populations of marmots reside in a high montane habitat where the growing season is short. Variations in growing season and temperature and moisture availability may affect fitness parameters. Predation is high with at least seven species preying on marmots. The polygynous social system of marmots is an adaptation to these environmental pressures. Most marmots live in social groups consisting of a resident male and from one to five females; fitness is highest in groups with three females. We examined demographic data from a core area of the study where most marmots live in social groups to determine if there were density-dependent effects. Using data from 1967 to 1998 we calculated a correlation matrix between density and overall survival; survival of young, yearling, and adult; mean and variance of litter size; net reproductive rate; and generation length. Only net reproductive rate was positively correlated with density, and a significant regression was found. During periods of relatively stable weather and low predation, harems grow or fission to optimum sizes with greater reproductive fitness; thus density and net reproductive rate covary.

KEY WORDS: density-dependence, fitness, Marmota flaviventris , social