Dynamics of Interacting Elk Populations within and Adjacent to Rocky Mountain National Park

• Published in: The Journal of wildlife management 2002-07, Vol.66 (3), p.757-775
• Main Authors: Lubow, Bruce C., Singer, Francis J., Johnson, Therese L., Bowden, David C.
• Format: Article
• Language: English
• Subjects: Animal and plant ecology; Animal populations; Animal, plant and microbial ecology; Animals; Biological and medical sciences; Deer; Demecology; Elk; Elks; Fundamental and applied biological sciences. Psychology; Mammalia; National parks; Parametric models; Parks & recreation areas; Population dynamics; Population ecology; Population estimates; Population size; Survival rates; Vertebrata; Wildlife ecology; Wildlife management
• ISSN: 0022-541X; 1937-2817
• DOI: 10.2307/3803141

We studied population subdivision and density-dependent and independent factors influencing population processes between 1965 and 2001 for elk (Cervus elaphus) inhabiting Rocky Mountain National Park (park) and the adjacent Estes Valley (town), Colorado, USA. Elk numbers within the park were held relatively constant by management controls until 1967, after which time they were allowed to increase without human interference. Radiotelemetry of 73 elk indicated limited exchange between the subpopulations; combined with clear distinctions in population dynamics, this suggests that these subpopulations are relatively independent despite the absence of physical barriers between them. The elk subpopulation within the park initially increased at 6.5%/year between 1968 and 1970, then growth gradually slowed-exhibiting density-dependent reductions both in calf survival and recruitment with increasing population size-and approached an estimated carrying capacity of 1,069 ± 55 (x̄ ± SE). Since 1991, this subpopulation has remained within ±5% of this equilibrium. The adjacent Estes Valley subpopulation grew at an estimated maximum 5-year average rate of 11.0% from 1979 to 1983 and is still increasing at 5.2%/year (1991-2001 average). Estimated town population currently is about 70% of our projected carrying capacity of 2,869 ± 415 elk based on projection of observed calf recruitment decline with increasing population. Both carrying-capacity estimates are consistent with independent estimates based on forage biomass and energy considerations. Adult cow survival rate was not found to differ between park and town, and we estimated a constant rate of 0.913 [95% CI = 0.911, 0.915]. Bull survival rates increased in the park from 0.52 to 0.79 between 1965 and 2001, but remained constant at 0.42 [0.35, 0.47] in the Estes Valley. Colder winter temperatures were correlated with reduced calf recruitment (calves:cow at age 0.5 yr) and with reduced calf survival (between age 0.5 and 1.5 yr) in town. Recruitment of town elk also increased with warmer summer temperatures and greater summer precipitation. No weather covariates were significantly correlated with calf recruitment or survival in the park. Declining calf recruitment has been nearly linear and similar in both the park and town. In the park, calf survival responded little to density when the population was well below carrying capacity, but responded at an increasing rate as the population neared carrying capacity. This patt