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Residual effects of nutrient additions were sustained in shrubs 4-8 years after fertilization stopped in a northern boreal forest in Yukon, Canada. We measured the growth rate of grey willow (Salix glauca L.) and bog birch (Betula glandulosa Michx.) twigs during the growing seasons of 1998, 2001, and 2002, 4-8 years after NPK fertilization from 1987 to 1994 had ceased. We also measured the nitrogen concentration of the 1998 growth tissue. Willow twigs had significantly higher growth rates in previously fertilized shrubs than control shrubs in these 3 years, even greater than differences observed during fertilization. Willow also had higher N concentration in fertilized twigs than control twigs. Birch growth was...
Categories: Publication; Types: Citation; Tags: M1-Ecosystems, M1-Flora
Categories: Publication; Types: Citation; Tags: M1-Birds
Predation is a central organizing process affecting populations and communities. Traditionally, ecologists have focused on the direct effects of predation--the killing of prey. However, predators also have significant sublethal effects on prey populations. We investigated how fluctuating predation risk affected the stress physiology of a cyclic population of snowshoe hares (Lepus americanus) in the Yukon, finding that they are extremely sensitive to the fluctuating risk of predation. In years of high predator numbers, hares had greater plasma cortisol levels at capture, greater fecal cortisol metabolite levels, a greater plasma cortisol response to a hormone challenge, a greater ability to mobilize energy and poorer...
Snow cover is a key environmental component for tundra wildlife that will be affected by climate change. Change to the snow cover may affect the population dynamics of high-latitude small mammals, which are active throughout the winter and reproduce under the snow. We experimentally tested the hypotheses that a deeper snow cover would enhance the densities and winter reproductive rates of small mammals, but that predation by mustelids could be higher in areas of increased small mammal density. We enhanced snow cover by setting out snow fences at three sites in the Canadian Arctic (Bylot Island, Nunavut, and Herschel Island and Komakuk Beach, Yukon) over periods ranging from one to four years. Densities of winter...
Categories: Publication; Types: Citation; Tags: M1-Mammals
Estimating population densities of small mammals (< 100 g) has typically been carried out by intensive livetrapping, but this technique may be stressful to animals and the effort required is considerable. Here, we used camera traps to detect small mammal presence and assessed if this provided a feasible alternative to livetrapping for density estimation. During 2010-2012, we used camera trapping in conjunction with mark-recapture livetrapping to estimate the density of northern red-backed voles (Myodes rutilus) and deer mice (Peromyscus maniculatus) in the boreal forest of Yukon, Canada. Densities for these 2 species ranged from 0.29 to 9.21 animals/ha and 0 to 5.90 animals/ha, respectively, over the course of this...
The Kluane forest is unusual in that it is less productive than other boreal forests because it lies in a rain-shadow zone in the Yukon Territory. Densities of the boreal red-backed vole Clethrionomys rutilus are known to be food-limited in the Kluane region, and its food sources, mostly plants, could be rainfall-limited. Above-average rainfall in the Kluane region could reduce the summer water deficit, which would in turn enhance primary production and reduce food limitation in voles, ultimately leading to a population outbreak. We experimentally tested these two predictions by irrigating three sites in the boreal forest from 1995 to 1999, and concurrently comparing numbers of voles and availability of their potential...
Categories: Publication; Types: Citation; Tags: M1-Birds


map background search result map search result map Cyclic dynamics of snowshoe hares on a small island in the Yukon Herbivores - Forest grouse and ptarmigan Is the relationship between predator and prey abundances related to climate for lynx and snowshoe hares? Arctic ground squirrel population collapse in the boreal forests of the Southern Yukon Why Do the Boreal Forest Ecosystems of Northwestern Europe Differ from Those of Western North America? Cyclic dynamics of snowshoe hares on a small island in the Yukon Why Do the Boreal Forest Ecosystems of Northwestern Europe Differ from Those of Western North America? Herbivores - Forest grouse and ptarmigan Is the relationship between predator and prey abundances related to climate for lynx and snowshoe hares? Arctic ground squirrel population collapse in the boreal forests of the Southern Yukon