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We evaluated evidence of an effect of climate on the numerical response of a coyote (Canis latrans) population to their keystone prey, snowshoe hares (Lepus americanus), in a Canadian boreal forest. Six a priori hypotheses of the coyote numerical response were developed that postulated linear, nonlinear, additive, and interactive effects of prey and climate. Model selection procedures showed the North Atlantic Oscillation (NAO) had the strongest effect on the coyote numerical response via its interaction with snowshoe hare density, while other large-scale climate indices had very weak effects. For a given snowshoe hare density, a negative value of the NAO amplified the abundance of coyote and a positive NAO decreased coyote abundance. We hypothesize that the coyote numerical response is ultimately determined by the coyote functional response influenced by winter conditions determined by the NAO. [ABSTRACT FROM AUTHOR]

Snowshoe hares ( Lepus americanus Erxleben, 1777) fluctuate in 9-10 year cycles throughout much of their North American range. These cycles show large variations in cyclic amplitude and we ask what factors could cause amplitude variation. We gathered data from 1976 to 2012 on hare numbers in the boreal forest of Alaska, Yukon, Northwest Territories, and northern British Columbia to describe the amplitude of hare fluctuations and to evaluate four possible causes. First, weather could cause variation in amplitude via hare reproduction or survival, but this mechanism does not fit our data. Second, bottom-up processes involving forest succession could explain amplitude variation through changes in winter forage availability, but succession is too slow a variable in our study areas. Third, plant defenses entrained by hare over-browsing in one cycle can produce variation in plant quality and quantity in subsequent cycles. A mathematical model suggests this is a possible explanation. Fourth, predator recovery following the cyclic low is inversely related to hare cyclic amplitude, and the existing data are consistent with this mechanism. A standardized regional monitoring program is needed to improve our understanding of cyclic amplitude variation in hares and the possible role of predators and winter foods in affecting amplitude. [ABSTRACT FROM AUTHOR]

The trophic dynamics of the Yukon boreal forest have been under investigation at the Kluane Lake Research Station since 1973. We monitored and conducted experiments on the major species in this ecosystem, except the large mammals (for logistic reasons). The central problem has been to determine the causes of the 9 - 10 year cycle of snowshoe hares, and to achieve this we carried out several large-scale experiments manipulating food supplies, predator pressure, and soil nutrient availability to test hypotheses that food, predation, or habitat quality regulate populations. The hare cycle is driven top-down by predators, and most hares die because they are killed by predators. Predators also cause stress in female hares, and the stress response seems to be responsible for the loss of reproductive potential in the decline and low phases of the hare cycle. Many of the specialist predators and some herbivores in this ecosystem fluctuate with the hare cycle. Arctic ground squirrels do, but red squirrels do not, being linked closely to white spruce seed masting years. Small rodents fluctuate in numbers in two patterns. Red-backed voles and four species of Microtus voles have a 3 - 4 year cycle that seems to be driven by food supplies and social behaviour. Deer mice, in contrast, have fluctuated dramatically in the 38 years we have monitored them, but not cyclically. White spruce seed production varies with temperature and rainfall, but was not affected by adding nutrients in fertilizer. Global warming and reduced hare browsing in the last 20 years have helped to increase the abundance of shrubs in these forests. It will be challenging to predict how this system will change as climatic warming proceeds, because even closely related species in the same trophic level respond differently to perturbations. We recommend continued monitoring of the major species in these boreal forests. [ABSTRACT FROM AUTHOR]

The trophic dynamics of the Yukon boreal forest have been under investigation at the Kluane Lake Research Station since 1973. We monitored and conducted experiments on the major species in this ecosystem, except the large mammals (for logistic reasons). The central problem has been to determine the causes of the 9 - 10 year cycle of snowshoe hares, and to achieve this we carried out several large-scale experiments manipulating food supplies, predator pressure, and soil nutrient availability to test hypotheses that food, predation, or habitat quality regulate populations. The hare cycle is driven top-down by predators, and most hares die because they are killed by predators. Predators also cause stress in female hares, and the stress response seems to be responsible for the loss of reproductive potential in the decline and low phases of the hare cycle. Many of the specialist predators and some herbivores in this ecosystem fluctuate with the hare cycle. Arctic ground squirrels do, but red squirrels do not, being linked closely to white spruce seed masting years. Small rodents fluctuate in numbers in two patterns. Red-backed voles and four species of Microtus voles have a 3 - 4 year cycle that seems to be driven by food supplies and social behaviour. Deer mice, in contrast, have fluctuated dramatically in the 38 years we have monitored them, but not cyclically. White spruce seed production varies with temperature and rainfall, but was not affected by adding nutrients in fertilizer. Global warming and reduced hare browsing in the last 20 years have helped to increase the abundance of shrubs in these forests. It will be challenging to predict how this system will change as climatic warming proceeds, because even closely related species in the same trophic level respond differently to perturbations. We recommend continued monitoring of the major species in these boreal forests. [ABSTRACT FROM AUTHOR]

Snowshoe hares ( Lepus americanus Erxleben, 1777) fluctuate in 9-10 year cycles throughout much of their North American range. Regional synchrony has been assumed to be the rule for these cycles, so that hare populations in virtually all of northwestern North America have been assumed to be in phase. We gathered qualitative and quantitative data on hare numbers and fur returns of Canada lynx ( Lynx canadensis Kerr, 1792) in the boreal forest regions of Alaska, Yukon, Northwest Territories, and northern British Columbia to describe synchrony in the time window of 1970-2012. Broad-scale synchrony in lynx fur returns was strong from 1970 to about 1995 but then seemed to break down in different parts of this region. Hare populations at 20 sites in Alaska, the Yukon, and Northwest Territories showed peak populations that lagged by 1-4 years during the 1990s and 2000s cycles. The simplest hypothesis to explain these patterns of asynchrony in hare cycles is the movement of predators from British Columbia north into the Yukon and then east into the Northwest Territories and west into Alaska. A traveling wave of these cycles is clearly seen in the lynx fur returns from western Canada and Alaska from 1970 to 2009. One consequence of a failure of synchrony is that hare predators like Canada lynx and Great-horned Owls ( Bubo virginianus (Gmelin, 1788)) can move from one adjacent area to the next within this region and survive long enough to prolong low densities in hare populations that have declined earlier. [ABSTRACT FROM AUTHOR]