Technical Bulletin No. 0893: Ecological Interactions Among Caribou, Moose, and Wolves: Literature Review

 Woodland caribou populations are declining in many areas of Canada and there is concern that the decline may be associated with timber harvesting. Caribou, moose, and wolves share a long evolutionary history and their relationships may become altered by large-scale landscape disturbance. This technical bulletin presents a review of scientific literature pertaining to the hypothesis that increases in moose and wolf populations after timber harvesting have adverse effects on caribou. Specifically, large-scale habitat changes that have allowed moose populations to increase and thereby sustain higher wolf numbers presumably have resulted in excessive predation on caribou, apparently resulting in caribou population declines. Differentiation of caribou by ecotype rather than phenotype has advantages for conservation purposes. The forest-dwelling ecotype of woodland caribou often move across extensive areas at low densities, and populations have been difficult to define and monitor. Woodland caribou and moose often partition habitats on the landscape, such that caribou tend to graze mostly lichens and occupy nutrient-poor forest types, while moose browse vascular plant species such as willows, which are associated with more productive environments. The relatively high reproductive potential of moose enables their populations to respond rapidly to a superabundance of forage produced after forest fires or logging. Carrying capacities for caribou increase more slowly and are likely to decline suddenly after such disturbances. Some caribou populations experience the effects of multiple predators such as grizzly bears, black bears, cougars, coyotes, wolverines, lynx, eagles, and humans. The predation rate is determined by the predator’s functional and numerical responses to changes in prey density.