Density Dependence and Survival of Elk in Northwestern Wyoming

Survival rates of elk (Cervus elaphus) were estimated from tag recovery data. Correlations of yearly survival rates of cow and female calf elk with climatic, hunter kill, and elk population density variables indicate that cow survival varies with climate, but female calf survival changes with both climate and cow population density. Although a variety of climatic, population density, and other environmental factors probably interact to determine elk survival, we could only demonstrate density-dependent survival in calf elk. Age-specific density dependence should be incorporated into models of elk population dynamics to ensure accurate predictions of elk population densities and maximum sustained yields. J. WILDL. MANAGE. 47(1):31-37 Modeling of optimum yield in wild ungulate populations is often based on an inverse relationship between population density and fecundity (Gross 1969, 1972; McCullough 1979). Simulation models used by many state wildlife agencies to determine harvest strategies incorporate this density-dependent reduction in reproductive rates, but assume that mortality is independent of population densities (Roelle and Bartholow 1977). Fowler (1981a) demonstrated that age-specificity of density-dependent mortality and reproduction can change the shape of a yield curve and significantly affect maximum sustained yield (MSY) population densities. Density-dependent mortality has been documented for a variety of large mammals (Fowler 1981b), but little information is available on sexand age-specific relationships between density and mortality in managed populations of North American ungulates. This information is prerequisite to successful modeling of MSY. The Wyoming Game and Fish Department has ear-tagged elk in northwestern Wyoming since 1943. Straley (1968) reported on an analysis of recovery data from these investigations in which average survival rates were calculated using composite-dynamic life table methods. Recently, several models have been proposed for the analysis of tag recovery data that do not rely on the unrealistic assumptions required by the composite-dynamic technique (Burnham and Anderson 1979). These models, which can be used to analyze data from either a single group of animals or multiple age classes within a group, allow for time-specific variation in survival and recovery rates. In this paper we calculate survival of Wyoming elk for selected years between 1951 and 1967 using tag recovery models developed by Brownie et al. (1978). We also analyze density-dependent and density-independent components of the environment that may affect female elk survival. We thank the Wyoming Game and Fish Department for providing data and M. D. Strickland, L. Irwin, J. Wilbrecht, R. Robbins, J. Straley, and J. Newman for assistance in interpreting these data. L. McDonald assisted with statistical analysis. Present address: Museum of Natural History, The University of Kansas, Lawrence, KS 66045. J. Wildl. Manage. 47(1):1983 31 This content downloaded from 157.55.39.255 on Sat, 16 Apr 2016 05:59:53 UTC All use subject to http://about.jstor.org/terms 32 ELK SURVIVAL IN NORTHWESTERN WYOMING * Sauer and Boyce