Aitken K.E.H.,University of British Columbia |
Aitken K.E.H.,Yukon College |
Martin K.,University of British Columbia |
Martin K.,Environment Canada
Journal of Wildlife Management | Year: 2012
Nest-site availability limits cavity-using populations in many harvested forests; however, little is known about the extent of nest-site limitation in mature forests with a full complement of excavator species and intact processes of cavity creation and loss. To examine the role of nest-site availability in limiting cavity-using populations in mature mixed conifer forests in central British Columbia, Canada, we conducted an 11-year before-after control-impact experiment in which we increased nest-site availability via nest box addition. Our 7 sites (3 treatments, 4 controls) had low cavity densities (<2/ha) prior to treatment and cavity occupation rates were also low (<10%/yr), which is a relationship often cited in the literature as evidence of non-limitation in cavity-nesting populations. Following nest box addition at our treatment sites, which tripled the availability of cavities, total density of bird and mammal nests more than tripled. Density of mountain chickadee (Poecile gambeli) nests increased 9-fold on treatment sites and returned to pre-treatment levels following box removal, suggesting that chickadee populations were limited by cavity availability at our study sites. Density of red squirrel (Tamiasciurus hudsonicus) and northern flying squirrel (Glaucomys sabrinus) nests and roosts also increased significantly at treatment sites following box addition and declined following box removal. We noted little change in chickadee or squirrel nest density at control sites monitored concurrently. Squirrels preferred large-sized over small-sized boxes, and significantly enlarged the entrance areas of small boxes by chewing, suggesting that there may have been a shortage of suitable nest and roost sites for them in our study area. We contend that low cavity occupancy rates may not accurately reflect nest-site availability for cavity nesters in mature forests, and that cavity size may influence the true availability of cavities on the landscape. Copyright © 2011 The Wildlife Society.
Krebs C.J.,University of British Columbia |
Boonstra R.,University of Toronto |
Boutin S.,University of Alberta |
Sinclair A.R.E.,University of British Columbia |
And 5 more authors.
Arctic | Year: 2014
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 fuctuate with the hare cycle. Arctic ground squirrels do, but red squirrels do not, being linked closely to white spruce seed masting years. Small rodents fuctuate 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 fuctuated 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. © The Arctic Institute of North America.
Kolpaschikov L.,Extreme North Agricultural Research Institute |
Makhailo V.,St Petersburg Institute For Informatics And Automation |
Russell D.E.,Yukon College
Ecology and Society | Year: 2015
The Taimyr wild reindeer herd, i.e., caribou (Rangifer tarandus), is one of the most important wildlife resources in the Russian Far North and may constitute the largest migratory Rangifer herd in the world. Over the last 60 years the herd has undergone a recovery from low numbers in the 1940s, reaching high densities by 1970 that concerned wildlife managers and domestic husbandry herds, with an 11.7% annual growth rate. At that time an aggressive commercial harvest of the herd was implemented, and organized wolf control was initiated with the goal of stabilizing herd numbers and injecting needed economic activity into the region. These actions dampened the rate of increase throughout the 1970s and 1980s to a 3.0% annual growth rate. From 1991, after the collapse of the Soviet Union and the loss of financial capability to sustain the commercial harvest and continue wolf control, the population again increased at a 5.6% annual growth rate, until peaking in 2000 at just more than 1 million animals. Since 2000 the herd has been in decline; harvesting, primarily unregulated, has increased; the wolf population has increased; and range conditions have deteriorated. Understanding what has occurred in the Taimyr range can provide North American managers with valuable lessons in understanding the large migratory herds on this continent, especially given that the social and political situation in Russia enabled intensive management, i.e., harvest and wolf control, that may not be able to be duplicated in North America. © 2015 by the author(s).
Christensen L.,Yukon College |
Krogman N.,University of Alberta
Ecology and Society | Year: 2012
The objective of this paper is to provide a preliminary discussion of how to improve our conceptualization of social thresholds using (1) a more sociological analysis of social resilience, and (2) results from research carried out in collaboration with the Champagne and Aishihik First Nations of the Yukon Territory, Canada. Our sociological analysis of the concept of resilience begins with a review of the literature followed by placement of the concept in the domain of sociological theory to gain insight into its strengths and limitations. A new notion of social thresholds is proposed and case study research discussed to support the proposition. Our findings suggest that rather than view social thresholds as breakpoints between two regimes, as thresholds are typically conceived in the resilience literature, that they be viewed in terms of collectively recognized points that signify new experiences. Some examples of thresholds identified in our case study include power in decision making, level of healing from historical events, and a preference for small-scale development over large capital intensive projects. © 2012 by the author(s). Published here under license by the Resilience Alliance.
Cubley J.F.,University of Calgary |
Cubley J.F.,Yukon College |
Pattison D.R.M.,University of Calgary
Canadian Journal of Earth Sciences | Year: 2012
The Grand Forks complex (GFC) is an elongate, north-south-trending metamorphic core complex in the Shuswap domain of southeastern British Columbia. It comprises predominantly upper-amphibolite- to granulite-facies paragneisses, schists, orthogneisses, amphibolites, and calc-silicates of the Paleoproterozoic to Paleozoic Grand Forks Group. The GFC is juxtaposed against low-grade rocks of the Quesnel terrane across two bounding Eocene normal faults: the Kettle River fault (KRF) on the east flank and the Granby fault (GF) on the west flank. Peak metamorphic Sil + Kfs ± Grt ± Crd (Sil, sillimanite; Kfs, potassium feldspar; Grt, garnet; Crd, cordierite) assemblages in paragneiss and Hbl ± Opx ± Cpx (Hbl, hornblende; Opx, orthopyroxene; Cpx, clinopyroxene) assemblages in amphibolite in the GFC formed at 750 ± 25 °C, 5.6 ± 0.5 kbar (1 kbar = 100 MPa; 20 ± 2 km depth). Stratigraphically overlying Sil + St-bearing pelitic schists (St, staurolite) within the complex record peak conditions of 600 ± 15 °C, 5.5 + 0.25 kbar. Crd + Ilm + Spl (Crd, cordierite; Ilm, ilmenite; Spl, spinel) and Crd + Qtz (Qtz, quartz) coronal textures in paragneiss, and Cpx + Opx + Pl + Mt (Pl, plagioclase; Mt, magnetite) symplectites in amphibolite, formed at 735 ± 20 °C, 3.3 ± 0.5 kbar, indicating hightemperature, near-isothermal decompression of the GFC of ~2.3 ± 0.7 kbar (~8.2 ± 2.5 km) from peak conditions. Transitional greenschist-amphibolite metamorphic assemblages in the hanging wall of the KRF indicate conditions of ~425 ± 25 °C and 2.2 ± 0.6 kbar (~8 ± 2 km depth), with local contact metamorphism around Jurassic intrusions as high as 630-650 °C at ~2.5 ± 0.5 kbar. The pressure contrast across the Kettle River fault prior to greenschist facies displacement was ~0.8 ± 0.7 kbar, for a vertical offset of ~2.9 ± 2.5 km. This is similar to estimates for the Granby fault on the west flank of the GFC. The GFC therefore experienced a twostage exhumation history: early high-temperature decompression at upper-amphibolite- to granulite-facies conditions, followed by lowtemperature exhumation at greenschist-facies conditions owing to movement on the Eocene Granby and Kettle River faults.