Skip to main content
Advanced Search

Filters: Tags: M1-Changes in Plant and Animal Distributon (X) > partyWithName: Boonstra, R. (X)

22 results (66ms)   

View Results as: JSON ATOM CSV
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...
thumbnail
Epigeous mushroom production in the boreal forest ecosystem varies dramatically from year to year. We tested the hypothesis that the aboveground production of epigeous mushrooms in the Kluane region, Yukon, could be predicted by summer rainfall. There is a single crop in this part of the boreal zone with maximum production during the first 2 weeks of August. We measured standing crops from 1993 to 2007 at 13 areas along 210 km of the Alaska Highway and Haines Road in the southwestern Yukon. Aboveground mushroom crops averaged 24 kg/ha wet weight but varied from 0.0 to 117 kg/ha over the 15 years of study, with a coefficient of variation among years of 143%. Epigeous mushroom production could be predicted from June...
No population increases without limit. The processes that prevent this can operate in either a density-dependent way (acting with increasing severity to increase mortality rates or decrease reproductive rates as density increases), a density-independent way, or in both ways simultaneously. However, ecologists disagree for two main reasons about the relative roles and influences that density-dependent and density-independent processes have in determining population size. First, empirical studies showing both processes operating simultaneously are rare. Second, time-series analyses of long-term census data sometimes overestimate dependence. By using a density-perturbation experiment on arctic ground squirrels, we...
No population increases without limit. The processes that prevent this can operate in either a density-dependent way (acting with increasing severity to increase mortality rates or decrease reproductive rates as density increases), a density-independent way, or in both ways simultaneously. However, ecologists disagree for two main reasons about the relative roles and influences that density-dependent and density-independent processes have in determining population size. First, empirical studies showing both processes operating simultaneously are rare. Second, time-series analyses of long-term census data sometimes overestimate dependence. By using a density-perturbation experiment on arctic ground squirrels, we...
Epigeous mushroom production in the boreal forest ecosystem varies dramatically from year to year. We tested the hypothesis that the aboveground production of epigeous mushrooms in the Kluane region, Yukon, could be predicted by summer rainfall. There is a single crop in this part of the boreal zone with maximum production during the first 2 weeks of August. We measured standing crops from 1993 to 2007 at 13 areas along 210 km of the Alaska Highway and Haines Road in the southwestern Yukon. Aboveground mushroom crops averaged 24 kg/ha wet weight but varied from 0.0 to 117 kg/ha over the 15 years of study, with a coefficient of variation among years of 143%. Epigeous mushroom production could be predicted from June...
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...
Live-trapping of animals in natural populations is one of the main ways to determine population processes. We examined the effects of live-trapping on the expression of N-methyl-D-aspartate (NMDA) receptor subunits in the hippocampus of snowshoe hares. Snowshoe hares were obtained either with or without the stress of live-trapping. The CA1, CA3 and dentate gyrus were dissected and analyzed for the presence of NMDA receptor subunits. Trapping resulted in a significant reduction of NMDA receptor 1 (NR1) in each of the regions examined but did not affect the levels of either NMDA receptor 2A or 8 (NR2A or NR2B). Co-immunoprecipitation analysis showed that the association between NR1 and NR2A was decreased in the trapped...
Live-trapping of animals in natural populations is one of the main ways to determine population processes. We examined the effects of live-trapping on the expression of N-methyl-D-aspartate (NMDA) receptor subunits in the hippocampus of snowshoe hares. Snowshoe hares were obtained either with or without the stress of live-trapping. The CA1, CA3 and dentate gyrus were dissected and analyzed for the presence of NMDA receptor subunits. Trapping resulted in a significant reduction of NMDA receptor 1 (NR1) in each of the regions examined but did not affect the levels of either NMDA receptor 2A or 8 (NR2A or NR2B). Co-immunoprecipitation analysis showed that the association between NR1 and NR2A was decreased in the trapped...
1. We examined the effects of food and predators on population limitation in the arctic ground squirrel (Spermophilus parryii plesius Richardson) in the boreal forest of the south-western Yukon. We focused on ground squirrel reproduction and overwinter survival. 2. Squirrel populations were monitored by live-trapping and radio-telemetry from 1993 to the spring of 1996 on four control and four experimental areas (one predator exclosure treatment, two food addition treatments, and one predator exclosure plus food addition treatment). 3. Predator exclusion increased body condition, percentage lactating, percentage weaning litters, litter size, and doubled population density relative to controls, but had no effect on...
thumbnail
We examined whether arctic ground squirrel (Spermophilus parryii plesius) populations in northern boreal forest in the Yukon Territory, Canada, were limited by food, predators, or a combination of both, during the decline and low phases of a snowshoe hare cycle. From 1990 to 1995, populations were monitored in large-scale (1 km2) experimental manipulations. Squirrels were studied on eight 9-ha grids: four unmanipulated control grids, two food-supplemented grids, a predator-exclosure grid, and a predator-exclosure + food-supplemented grid. Population density was measured on all grids by livetrapping and active-season survival was measured using radiotelemetry. Population densities were lowest in 1992 and 1993 (2...
Epigeous mushroom production in the boreal forest ecosystem varies dramatically from year to year. We tested the hypothesis that the aboveground production of epigeous mushrooms in the Kluane region, Yukon, could be predicted by summer rainfall. There is a single crop in this part of the boreal zone with maximum production during the first 2 weeks of August. We measured standing crops from 1993 to 2007 at 13 areas along 210 km of the Alaska Highway and Haines Road in the southwestern Yukon. Aboveground mushroom crops averaged 24 kg/ha wet weight but varied from 0.0 to 117 kg/ha over the 15 years of study, with a coefficient of variation among years of 143%. Epigeous mushroom production could be predicted from June...
Epigeous mushroom production in the boreal forest ecosystem varies dramatically from year to year. We tested the hypothesis that the aboveground production of epigeous mushrooms in the Kluane region, Yukon, could be predicted by summer rainfall. There is a single crop in this part of the boreal zone with maximum production during the first 2 weeks of August. We measured standing crops from 1993 to 2007 at 13 areas along 210 km of the Alaska Highway and Haines Road in the southwestern Yukon. Aboveground mushroom crops averaged 24 kg/ha wet weight but varied from 0.0 to 117 kg/ha over the 15 years of study, with a coefficient of variation among years of 143%. Epigeous mushroom production could be predicted from June...
No population increases without limit. The processes that prevent this can operate in either a density-dependent way (acting with increasing severity to increase mortality rates or decrease reproductive rates as density increases), a density-independent way, or in both ways simultaneously. However, ecologists disagree for two main reasons about the relative roles and influences that density-dependent and density-independent processes have in determining population size. First, empirical studies showing both processes operating simultaneously are rare. Second, time-series analyses of long-term census data sometimes overestimate dependence. By using a density-perturbation experiment on arctic ground squirrels, we...
thumbnail
The 10-year cycle of abundance in the snowshoe hare, Lepus americanus, is one of the most striking features of the ecology of the boreal forests. Ten-year snowshoe-hare cycles in Canada were first analyzed quantitatively by wildlife biologists in the 1960s, using the meticulous fur-trading records of the Hudson Bay Company, which was founded in 1671. The rise and fall in the Canada lynx, a specialist predator of snowshoe hares, was shown to mirror the rise and fall of its prey population. Cycles appear to challenge the implicit assumption that there is a balance in nature. Large-scale experiments in the Yukon have shown that the snowshoe-hare cycle is a product of an interaction between predation and food supply,...
map background search result map search result map Experimental manipulation of predation and food supply of arctic ground squirrels in the boreal forest What Drives the 10-Year Cycle of Snowshoe Hares? Climatic determinants of berry crops in the boreal forest of the southwestern Yukon Mushroom crops in relation to weather in the southwestern Yukon Mushroom crops in relation to weather in the southwestern Yukon Climatic determinants of berry crops in the boreal forest of the southwestern Yukon Experimental manipulation of predation and food supply of arctic ground squirrels in the boreal forest What Drives the 10-Year Cycle of Snowshoe Hares?