Ecologia De Poblaciones

OIKOS 101: 591–601, 2003

Assessing differential prey selection patterns between two sympatric large carnivores
Jason S. Husseman, Dennis L. Murray, Gary Power, Curt Mack, C. R. Wenger and Howard Quigley

Husseman, J. S., Murray, D. L., Power, G., Mack, C., Wenger, C. R. and Quigley, H. 2003. Assessing differential prey selection patterns between two sympatric large carnivores. – Oikos 101:591– 601. Several conceptual models describing patterns of prey selection by predators have been proposed, but such models rarely have been tested empirically, particularly with terrestrial carnivores. We examined patterns of prey selection by sympatric wolves (Canis lupus) and cougars (Puma concolor) to determine i) if both predators selected disadvantaged prey disproportionately from the preypopulation, and ii) if the specific nature and intensity of prey selection differed according to disparity in hunting behavior between predator species. We documented prey characteristics and kill site attributes of predator kills during winters 1999– 2001 in Idaho, and located 120 wolf-killed and 98 cougar-killed ungulates on our study site. Elk (Cer6us elephus) were the primary prey for bothpredators, followed by mule deer (Odocoileus hemionus). Both predators preyed disproportionately on elk calves and old individuals; among mule deer, wolves appeared to select for fawns, whereas cougars killed primarily adults. Nutritional status of prey, as determined by percent femur marrow fat, was consistently poorer in wolf-killed prey. We found that wolf kills occurred in habitat that was morereflective of the entire study area than cougar kills, suggesting that the coursing hunting behavior of wolves likely operated on a larger spatial scale than did the ambush hunting strategy of cougars. We concluded that the disparity in prey selection and hunting habitat between predators probably was a function of predator-specific hunting behavior and capture success, where the longer prey chases andlower capture success of wolf packs mandated a stronger selection for disadvantaged prey. For cougars, prey selection seemed to be limited primarily by prey size, which could be a function of the solitary hunting behavior of this species and the risks associated with capturing prime-aged prey. J. S. Husseman and D. L. Murray, Dept of Fish and Wildlife Resources, Uni6. of Idaho, Moscow, ID 83844-1136, USA ( jason – husseman@hotmail.com). Present address of DLM: Depts of Biology and En6ironmental and Resource Studies, Trent Uni6., Peterborough, ON, K9J 7B8 Canada. – G. Power, Lemhi County Winter Predator Study, Salmon, ID 83467, USA. – C. M. Mack, Nez Perce Tribe, PO Box 365, Lapwai, ID 83501, USA. – C. R. Wenger, USDA Forest Ser6ice, Salmon-Challis National Forest, Salmon, ID 83467, USA. –H. Quigley, Hornocker Wildlife Institute, Bozeman, MT 59718, USA.

The patterns of prey selection exhibited by various predator species tend to be shaped by a suite of factors, including predator and prey behavior, morphology, and habitat requirements related to hunting or escape (Bakker 1983, Kruuk 1986). In general, such factors interact to affect predator-prey encounter and captureprobabilities, and thus ultimately determine prey selec-

tion patterns occurring within a particular predatorprey system (Pastorok 1981, Sih and Moore 1990, Litvak and Leggett 1992). Yet, even within a given prey species the attributes of depredated individuals may vary spatially, temporally, or between predator species, implying that patterns of differential prey vulnerability to predation need notalways follow a standard model.

Accepted 17 October 2002 Copyright © OIKOS 2003 ISSN 0030-1299
OIKOS 101:3 (2003)

591

Indeed, while the notion that predators select disadvantaged individuals disproportionately from the prey population has received widespread empirical support (Errington 1946, Curio 1976, Keith et al. 1984, Murray 2002), many studies have failed to detect such patterns...