Document: JOH-3-56-7

Elk and bison: Foraging in the landscape of fear of Yellowstone National Park .

LAUNDRÉ, J.W.* ^1,2 and L.HERNÁNDEZ ²

Idaho State University, Pocatello, ID 83209 ¹
Instituto de Ecología, A.C.-CEISS, Aldama, Chi, Mexico ²

Abstract:
In 1999, it was reported that elk (Cervus elaphus) and bison (Bison bison) in Yellowstone National Park responded behaviorally to the reintroduction of wolves (Canis lupus) by significantly increasing their vigilance rates. Subsequently, we investigated if wolves were also affecting habitat use patterns and diet quality of elk and bison. Habitat use was determined by counting the number of pellet groups (elk) or flops (bison) we found in 10 m² sample plots located every 50 m from the forest edge to 500 m into the open meadow. Diet quality was assessed by measuring fecal nitrogen, phosphorous, and protein of both species. Data on habitat use and diet were collected from areas with and without wolves in 1998 and 1999. Relative to habitat use in areas with wolves, the number of elk pellet groups per 10 m² was significantly (P = 0.001, r² = 0.657) and negatively related to distance from the forest edge. No difference was found in the number of pellet groups per distance from edge in non-wolf areas. There was no difference for wolf nor non-wolf areas in the number of bison droppings per distance. In areas with wolves, percent fecal nitrogen (1.6 %, SE = 0.40), protein (9.8%, SE = 0.57), and phosphorus (2,097 mg/kg, SE = 258.6) were significantly less than non-wolf areas (N = 2.1 %, SE = 0.68; Protein = 13.1 %, SE = .67, P = 4,110 mg/kg, SE = 532.2). Again, no differences were seen in these parameters for bison. Habitat use results suggest, in addition to increased vigilance, elk are further responding to the landscape of fear established by wolves by shifting their habitat use patterns. Results of diet analyses further indicate this shift is to poorer quality but likely safer forage areas. It is proposed this shift in habitat use and reduction in diet quality will have significant long range impacts on the elk population as well as the vegetative communities of Yellowstone Park. Bison, however, have not responded in this manner, possibly increasing vigilance for this species is sufficient to the lower predation risk relative to wolves.

Keywords: elk, bison, wolves, diets, habitat use

This abstract is being presented at: 4:30 PM in session:
Oral Session #17: Mammalian Herbivory.