Estimates of Elk Summer Range Nutritional Carrying Capacity Constrained by Probabilities of Habitat Selection

Abstract

We used habitat-selection data from a reintroduced population of elk (Cervus elaphus) in northeastern Nevada, USA, to develop a resource-selection function to adjust nutritional carrying capacity estimates. Constrained estimates provide population levels that minimize overuse of key foraging communities. We estimated economic nutritional carrying capacity (INCC) for 236-kg lactating cow elk in autumn 1999 and 2000 to reflect expected animal performance under maintenance (2,550 kcal/kg DM) and good (2,750 kcal/kg DM) levels of standing digestible energy. We used our resource-selection function to redistribute INCC densities (RSFD) for aspen (Populus tremuloides), conifer, curl-leaf mountain mahogany (Cercocarpus ledifolius), sagebrush (Artemisia spp.)–herb, and snowbrush ceanothus (Ceanothus velutinus) cover types across the summer range and then adjusted original INCC estimates according to these RSFD when expected densities exceeded original INCC estimates. Maintenance performance INCC estimates were 2,533 cow elk (95% CI: 1,327–3,739) in 1999 and 1,655 (95% CI: 886–2,424) in 2000. Good performance INCC estimates were 2,264 cow elk (95% CI: 1,150–3,378) in 1999 and 1,100 (95% CI: 384–1,816) in 2000. The best habitat model provided evidence that forage availability and distance to water influenced habitat selection. Adjustments in INCC for 1999 and 2000 and at both performance levels corresponded to decreases of 18–35% in original INCC estimates. Decreases were attributed to more cow elk predicted by RSFD to be in aspen, conifer, and sagebrush–herb cover types than predicted by INCC. Each year, RSFD predicted that fewer elk would use mahogany and snowbrush cover types than original INCC models. The adjusted carrying capacity estimates provided population levels that should avoid appreciable alteration of aspen, conifer, and sagebrush–herb communities while ensuring nutritious resources during lean periods. Our paper provides a critical refinement for nutritional carrying capacity models through incorporating prediction of animal selection of nutritional resources.