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| Technical Bulletin No. 0893: Ecological Interactions Among Caribou, Moose, and Wolves: Literature Review |
| Type: |
Technical Bulletin No. 0893 |
| Published: |
December 2004 |
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| File Size: |
614 KB |
Category: |
Reports |
| File Type: |
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(Adobe PDF) |
Frequency: |
As Needed |
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| Bibliographic Citation |
| National Council for Air and Stream Improvement, Inc. (NCASI). 2004. Ecological Interactions Among Caribou, Moose, and Wolves: Literature Review. Technical Bulletin No. 0893. Research Triangle Park, NC: National Council for Air and Stream Improvement, Inc. |
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| Abstract |
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. Some of the most viable caribou populations are those that employ anti-predator strategies which reduce encounter rates with wolves at calving time. These include migrating away from wolf denning habitat, seeking refuge on islands, bogs, and shorelines, and parturient females dispersing away from caribou concentrations.
Food selection by wolves is influenced by profitability relative to energetic costs of travel, especially in snow, and dangers in attacking large prey. If primary prey become less abundant, it may be more profitable for wolves to switch to another prey species. Critical thresholds in predator and prey densities affect population dynamics. In some areas, woodland caribou populations are too low to sustain wolves without alternate prey such as moose. Caribou appear in decline or may be eliminated in areas where wolves exceed critical densities. On the other hand, caribou populations have been known to change by several orders of magnitude, especially where herds are migratory and alternate prey for wolves are low in numbers or lacking. Several factors such as age, nutritional state, season, disease, parasites, and genetic load are capable of affecting caribou vulnerability to predation. The very young and the very old are usually the most heavily preyed upon.
Recent changes in ungulate and carnivore distributions may be influenced by climate change and human activities. Measures implemented to conserve woodland caribou populations include hunting restrictions, reintroductions, predator control, parks and protected areas, and national and provincial recovery strategies.
Caribou habitat and commercial forest overlap in some regions and the effects of forestry on caribou vary according to the ecological setting. Roads and seismic-exploration trails may allow greater penetration of wolves into areas occupied by caribou, and vehicular traffic may displace caribou into closer proximity to moose and wolves. The design of forest harvest pattern may significantly affect predator-prey relationships. A mosaic of small cutovers across extensive areas or cutting upland sites in close proximity to fen/bog habitat may be undesirable for caribou management. Silvicultural activities that are compatible with lichen retention and discourage moose browse production are expected to be the most beneficial for caribou. Although fire control may conserve caribou habitat in the short term, fire is an integral part of the boreal forest and this animal is adapted to a fire environment. Further research and management needs have been recommended. |
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