Abstract
Predation, especially wolf (Canis lupus) predation, limits many North American caribou (Rangifer tarandus) populations below the density that food resources could sustain. The impact of predation depends on the parameters for the functional and numerical response of the wolves, relative to the potential annual increment of the caribou population. Differences in predator-avoidance strategies largely explain the major differences in caribou densities that occur naturally in North America. Caribou migrations that spatially separate caribou from wolves allow relatively high densities of caribou to survive. Non-migratory caribou that live in areas where wolf populations are sustained by alternate prey can be eliminated by wolf predation.
Highlights
Predation, especially wolf (Cams lupus) predation, limits many North American caribou (Rangifer tarandus) populations below the density that food resources could sustain
Strategy or when predators are sustained by alternate. It appears that caribou populations in the boreal prey species even when the prey species of interest forests of North America historically co-existed is at low densities
Numerous limiting factors including winter severity, insect harassment, diet quality and accidents undoubtedly have an impact on caribou populations and result in year to year fluctuations in caribou populations
Summary
In the absence of major predators or high levels of human harvest, caribou and reindeer (Rangifer tarandus) populations generally increase until their populations become regulated by densitydependent competition for food (Klein 1968, Leader-Williams 1980, Skogland 1985). Annual increment is small because there is little competition and the population growth rate is high, there is a small breeding population. Annual increment again becomes small because despite an abundant breeding population, the growth rate is low due to density-dependent competition for resources. In the absence of predators or harvesting, the population will generally increase until competition for resources reduces the growth rate and annual increment to zero. Rangifer populations regulated by competition for food resources often attain densities exceeding 2/km (Table 1)
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