Dynamics of a Colonizing Elk Population

Abstract

The estimated rate of increase (r) for a naturally colonizing elk (Cervus elaphus nelsoni) population in the shrub-steppe region of southcentral Washington was 0.20 for 1975-86 (2-13 yr post-colonization). From 1982 to 1986, r was 0.30. Survival of all age classes was high. During 1982-86 0.76 calves/female were weaned if 2-year-olds were included, or 0.91 calves/female if 2-year-olds were excluded. Age-specific pregnancy and survival rates were combined in a model to evaluate the impact of various parameter values on rates of increase. Observations and simulation results suggest that the high rate of increase observed was due to high first-year survival and probably substantial reproductive output from 2-year-old females. J. WILDL. MANAGE. 52(2):309-313 Although elk are not endigenous to the arid shrub-steppe of the Columbia River Basin, Washington, a natural colonization has established a resident population in the region (Rickard et al. 1977). This nonmigratory population increased since colonization in 1972, approaching a rate of increase that may be a practical maximum for the species (Murphy 1963, Raedeke et al. 1986, Gogan and Barrett 1987). Data on elk population dynamics during the early stages of population growth are rare, particularly for naturally colonizing populations (Gogan and Barrett 1987), and data on elk population dynamics in the shrub-steppe biome are nonexistent. In this paper, we present data on the dynamics of this rapidly increasing elk population and we examine the reproductive and survivorship schedules required to approach the practical maximum rate of increase. This work was supported by the U.S. Department of Energy under contracts DE-ACO676RLO 1830 and DE-AMO6-76RLO 2225. We thank W. H. Rickard and the National Environmental Research Park Program at Hanford for logistical support. R. D. Taber and K. J. Raedeke provided useful advice.