Foraging niche overlap among Rocky Mountain elk (Cervus elaphus nelsoni), Rocky Mountain mule deer (Odocoileus hemionus hemionus), and cattle (Bos taurus) was studied for 2 years on 37 000 ha of nonforested foothill and mountain habitat in northwestern Wyoming. Microhistological analysis was used to quantify botanical composition of ungulate diets from monthly fecal collections. Feeding habitat use was determined through monthly surveys from fixed-wing aircraft to record nonsolitary animals in nonforested habitat. Kulcyznski's similarity index was used to calculate dietary and feeding habitat overlap among the 3 ungulates, and these 2 indices were multiplied together to estimate foraging niche overlap. In all seasons, elk and cattle consumed grass-dominated diets (mean ¼ 61% and 81%, respectively), although elk diets were more diverse. Mule deer consumed more forbs and shrubs than either elk or cattle (P , 0.10). Foraging niche overlap was high (45%) between mule deer and elk in spring. Cattle in summer and fall had !60% foraging niche overlap with elk in spring, indicating that, in spring, elk foraged in many of the same places (largely sagebrush grassland) and ate diets similar in botanical composition to what cattle did during summer and fall (principally Festuca idahoensis, Pseudoroegneria spicata, and Achnatherum spp.). Foraging niche overlap also was high (41%-51%) between elk in winter and cattle in summer and fall. Therefore, if competitive or complementary relationships existed between elk and cattle, these interactions most likely occurred on sagebrush grasslands where cattle use in summer-fall was followed by elk use in winter-spring. We recommend that resource managers focus their forage utilization and range trend monitoring in foothill sagebrush grasslands. ResumenSe estudió el traslape del nicho de forrajeo entre el alce de las Montañ as Rocallosas, (Cervus elaphus nelsoni), el venado mula de las Montañ as Rocallosas (Odocoileus hemionus hemionus) y el ganado (Bos taurus); el estudio se condujo por dos añ os en 37 000 ha de hábitats deforestado al pie de montañ a y montañ oso situados en el noroeste de Wyoming. La composició n botá nica de la dieta de los ungulados se determinó a partir de muestras fecales colectadas mensualmente y con el uso del análisis microhistoló gico. El uso de há bitat alimenticio se determinó a través de muestreos mensuales por medio de un dispositivo aéreo de alas fijas para registrar los animales no solitarios en el há bitat deforestado. El índice de similaridad de Kulcyznski se uso para calcular el traslape de la dieta y del há bitat alimenticio entre los tres ungulados, y estos dos índices se multiplicaron para estimar el traslape del nicho de forrajeo. En todas las épocas de añ o, el alce y el ganado consumieron dietas dominadas por zacates (media ¼ 61% y 81%, respectivamente), aunque las dietas del alce fueron má s diversas. El venado mula consumió más hierbas y arbustos que el alce y el ganado (P , 0.10). En primavera, el traslape del nicho de forrajeo fue a...

No abstract

Computer simulation was used to determine the effects of wild elk (Cervus elaphus) on available forage, cattle herd size, and ranch gross margin in southwestern Montana beef cow-calf production systems. Data collected from 5 southwestern Montana ranches were used to develop input parameters for bio-economic models of elk forage harvest and beef production. Input parameters described ranch resources, animal inventories, and animal management. Cattle herd size ranged from 241 to 1147 head. Elk numbers varied by season within ranch and ranged from 49 to 421 head. Ranches were simulated as currently managed with elk present and with 10, 20, 30, and 100% of the elk removed. Simulated management scenarios were replicated 10 times. Data from each ranch were analyzed by one-way analysis of variance. Cattle herd size, gross margin, and available forage significantly (P < 0.05) increased when all elk were removed; however, the magnitude of these effects differed among ranches. Removal of all elk permitted cattle herd size to increase from 7 to 32% across ranches. Annual costs of elk on the 5 ranches (i.e.