Predator-Prey Relationships
The following are notes from a recent Ungulate-Predator Relationship Workshop. These studies produced some very interesting numbers and show that some theories, such as predators only taking the old/weak prey, are just not true.

Impacts of Wolves and Mountain Lions on
Deer and Elk in Eastern Idaho

Dr. Dennis Murray, University of Idaho

Dr. Murray studied impacts of wolves and mountain lions on deer and elk in eastern Idaho. Predator/prey theory says additive predation would eventually eliminate prey completely. Compensatory predation is "taking only those animals who are doomed anyway." If predators also take viable healthy animals it can result in better food and conditions for remaining prey, which may result in increased offspring. To determine predation rates on prey populations, predators and prey must be studied year-around. Murray's study updates figures on Gary Powers' study in Unit 28. Wolves are coursing predators that chase prey over long distances in open habitat and have a relatively low success rate, selecting substandard prey. The success rate on elk is 20 percent.

Cougars hunt in heavier cover and have variable selection, often selecting prime-condition prey. One researcher reported 82 percent success rate on elk and deer. Wolves are more likely to be compensatory predators, cougars additive. Powers' study covered 1999-2001. Wolves and cougars were radio-collared and tracked and their kills analyzed. Deer and elk kills were nearly identical in proportion, with winter kills running about 25 percent deer, for both predators. In elk kills, both selected calves when possible. In deer, the majority of lion kills were adults, but for wolves it was fawns. Wolves and cougars both killed elk that were significantly older than did hunters. The animals killed by cougars had higher bone-marrow fat levels than those killed by wolves, indicating the prey was in better shape — again, the wolves being compensatory predators. Wolves utilized 80 percent of carcasses, cougars about 85. Each pack of wolves killed an animal every 2.2 to 2.7 days, on average. Cougars killed an animal about every nine days. Wolves are taking about 2.1 to 2.5 percent of the elk population in unit 28; cougars about 10-15 percent. Likely effects of predators on prey in Idaho are that cougar predation is additive and wolf predation is mildly additive/compensatory. Keep in mind this study was a small snapshot in time and in space. More study needs to be done on prey, and predator-prey studies need to be done under a range of predator and prey densities. Wolf harassment, even if they don't make a kill, causes "sublethal" impacts that stress out animals and cause further mortalities. If the study were done year-around, there would be more healthy animals in the mortalities.

Modeling Impacts of Wolves on Elk in Idaho
Jim Hayden, Panhandle Region wildlife manager

Hayden did modeling impacts of wolves on elk in Idaho. Calf ratios began to decline in some areas in the early 1990s, factors being severe winters in the Panhandle and large fires during 1988-2000 in central Idaho. Adding wolves in the mid-1990s was an additive impact. One model showed that in Unit 28, elk would stay fairly stable in good habitat over five years but would decline seriously in poor habitat. With no wolves their numbers would increase sharply. Units 66 and 69 showed the same. Units 10A and 15 were places where the model did not track known data. In Unit 28, population is declining by 13 percent annually. The second model showed that with 36 wolves instead of 18, the decline would be greater, but without wolves it would still be almost 10 percent, indicating something else is going on. The model shows how the population would change based on changing the number of kills by hunters, or the numbers of wolves, lion or bears in the unit. Conclusion is that adjusting populations of predators and hunters will compensate for wolf impacts in some units.

Multiple Predator Impacts in the Northwest
Dr. Kyran Kunkel, Turner Endangered Species Fund

Dr. Kunkel's studies took place near Glacier National Park on private and public lands. Different ecosystems have different prey species and interaction will be different. In his study, wolves peaked in about 1993 and then declined. There were wolves, mountain lions, black and grizzly bears in the area. Humans were also included as predators because there was harvest in the area. They captured and radio-collared adult female moose, whitetail deer and elk as well as cougars and wolves. There were 51 wolves in four packs during the 1987-95 study. Of collared deer, 73 percent survived. Cougars accounted for 30.2 percent of mortalities and wolves 25 percent. Bears were the primary predator on moose, and lions on elk. Hunter success declined due to predator impacts including hunting and low recruitment. Whitetail deer were the primary prey for wolves and lions. Predators were not killing animals which were "going to die anyway." Predation proved to be additive, not compensatory. Wolves located whitetail winter ranges and stayed in those areas to hunt, but would kill an elk or moose rather than deer if given the chance. Wolf kill rates are not stable: they varied 12-fold over the course of the study. When prey numbers declined, predator reproduction and numbers declined. Where cover was open and terrain steep, wolf kills declined. As game declined, wolf packs trespassed on each other's territory and were killed, resulting in a decline in wolf numbers and in reproduction. Cougars also declined, often starving to death. The study showed that if wolves were the only predator, prey numbers would not decline but in the multi-predator system, there will be ups and downs in both predator and prey numbers. Managing hunter harvest is a good response when prey declines.

Wolf Interactions and Impacts in British Columbia
Dr. Tom Bergerud, University of British Columbia

Dr. Bergerud studied wolf interactions and impacts in a multi-ungulate system in British Columbia. Bergerud published a paper in the Journal of Wildlife Management in 1974, which stated that predation by wolves and bears is recognized as a major limiting factor on caribou and moose. If wolf numbers could be managed, game numbers would not decline. Without management, wolves will regulate the ungulates, with the biggest impact being on recruitment. Bergerud believes that elk should not be countec on their winter range to determine density, but should instead be counted during calving. When wolves were poisoned in BC in 1982, prey species boomed and hunter success also; then wolves boomed which was followed by a decline in prey and hunter success. If you want to recruit 24 elk calves per 100, you can support nine wolves per 1000 kilometers squared. Bergerud predicts major impacts by wolves on game populations, including a major decline in the elk herd in northern Yellowstone.

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