Whitehorse, Canada
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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.

Cubley J.F.,University of Calgary | Cubley J.F.,Yukon College | Pattison D.R.M.,University of Calgary | Archibald D.A.,Queen's University | Jolivet M.,CNRS Geosciences Laboratory of Rennes
Canadian Journal of Earth Sciences | Year: 2013

The Grand Forks complex (GFC) is a metamorphic core complex within the composite Shuswap complex in the southern Omineca belt of the Canadian Cordillera. It is juxtaposed against the surrounding low-grade rocks of the pericratonic Quesnel terrane by outward-dipping Eocene normal faults. The GFC attained peak metamorphic conditions of 750-800 °C and 5.5-6.0 kbar (1 kbar = 100 MPa) in the late Paleocene to early Eocene, followed by ~2.5 kbar of near-isothermal decompression at upper-amphibolite to granulite facies conditions (~725-750 °C) in the early Eocene. Subsequent low-temperature greenschist-facies exhumation (~0.7-1.5 kbar) was accommodated by the brittle-ductile Kettle River normal fault (KRF) on the east flank of the complex and the Granby fault (GF) on the west flank. This study presents 16 new 40Ar/39Ar hornblende and biotite dates from the GFC and low-grade rocks in the hanging walls to the KRF and GF. Cooling of the GFC through the closure temperature of hornblende (~530 °C) is constrained to the interval between ~54 and 51.4 ± 0.5 Ma, whereas cooling through the closure temperature of biotite (~280 °C) occurred at 51.4 ± 0.2 Ma. In the hanging wall of the KRF, cooling through the closure temperature of hornblende and biotite occurred nearly coevally at 51.7 ± 0.6 Ma and 51.0 ± 1.0 Ma, respectively. Five apatite fission track dates (closure temperature ~110 °C) from the GFC and adjacent hanging walls are indistinguishable within error, yielding an average age of 34.6 ± 2.0 Ma. The lack of difference in biotite and apatite ages between the GFC and the low-grade hanging wall rocks against which it is juxtaposed suggests no significant movement on the KRF and GF after ca. 51 Ma. Results from this study and a previous study on U-Pb dating of the GFC document rapid cooling of the GFC in excess of 200 °C/Ma in a 4 Ma interval between 55 and 51 Ma (Eocene). This rapid phase of exhumation of the GFC was followed by 15 Ma of slow cooling (~10 °C/Ma) of the joined GFC and hanging wall between ~280 °C (biotite closure) and ~110 °C (apatite closure).

Reid D.G.,Wildlife Conservation Society | Bilodeau F.,Laval University | Krebs C.J.,University of British Columbia | Gauthier G.,Laval University | And 5 more authors.
Oecologia | Year: 2012

The insulative value of early and deep winter snow is thought to enhance winter reproduction and survival by arctic lemmings (Lemmus and Dicrostonyx spp). This leads to the general hypothesis that landscapes with persistently low lemming population densities, or low amplitude population fluctuations, have a low proportion of the land base with deep snow. We experimentally tested a component of this hypothesis, that snow depth influences habitat choice, at three Canadian Arctic sites: Bylot Island, Nunavut; Herschel Island, Yukon; Komakuk Beach, Yukon. We used snow fencing to enhance snow depth on 9-ha tundra habitats, and measured the intensity of winter use of these and control areas by counting rodent winter nests in spring. At all three sites, the density of winter nests increased in treated areas compared to control areas after the treatment, and remained higher on treated areas during the treatment. The treatment was relaxed at one site, and winter nest density returned to pre-treatment levels. The rodents' proportional use of treated areas compared to adjacent control areas increased and remained higher during the treatment. At two of three sites, lemmings and voles showed significant attraction to the areas of deepest snow accumulation closest to the fences. The strength of the treatment effect appeared to depend on how quickly the ground level temperature regime became stable in autumn, coincident with snow depths near the hiemal threshold. Our results provide strong support for the hypothesis that snow depth is a primary determinant of winter habitat choice by tundra lemmings and voles. © 2011 Springer-Verlag.

Krebs C.J.,University of British Columbia | Boonstra R.,University of Toronto | Gilbert S.,Yukon College | Reid D.,Wildlife Conservation Society | And 2 more authors.
Journal of Mammalogy | Year: 2011

Management agencies and quantitative ecologists need robust estimates of population density. The best way of converting population estimates of livetrapped small mammals to population density is not clear. We estimated population density on livetrapping grids with 4 estimators applied to 3 species of boreal forest and 3 species of tundra rodents to test for relative differences in density estimators. We used 2 spatial estimators proposed by Efford (2009) and 2 traditional boundary-strip estimators designed for grid livetrapping. We analyzed markrecapture data from 104 trapping sessions from the boreal forest at Kluane, Yukon (n = 4,818 individuals), and 56 trapping sessions from tundra areas of Herschel Island and Komakuk Beach in northern Yukon (n = 1,327 individuals). For boreal forest rodents on average both boundary-strip methods produced density estimates larger than Efford's maximum-likelihood (ML) estimator by as much as 50% at all population densities up to 25 animals/ha. For tundra rodents both boundary-strip methods produced density estimates smaller than Efford's ML at low density (<1.5/ha) and larger than Efford's ML density by 36-63% at high density (25/ha). Efford's inverse prediction estimator produced larger density estimates than the ML estimator by 4% for the boreal forest and 32% for the tundra rodents. Relationships were high between all the estimators, such that trends in density could be inferred from all methods. Determining the bias in population density estimators in small mammals will require data from populations spatially closed and completely enumerated. For our small mammals Efford's ML estimator typically provided density estimates smaller than those produced by conventional boundary-strip estimators. © 2011 American Society of Mammalogists.

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.

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).

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.

Hare P.G.,Government of Yukon | Thomas C.D.,Government of Yukon | Topper T.N.,Yukon College | Gotthardt R.M.,Government of Yukon
Arctic | Year: 2012

Since 1997, more than 207 archaeological objects and 1700 faunal remains have been recovered from 43 melting ice patches in the southern Yukon. The artifacts range in age from a 9000-year-old (calendar) dart shaft to a 19th-century musket ball. This paper provides an update on Yukon ice patch research and summary data on select areas of research conducted since 2003. More than 200 radiocarbon dates have been run on ice patch archaeological and faunal materials, and these data allow us to observe and comment on apparent temporal trends. Analysis undertaken since 2003 has improved our understanding of the development and maintenance of hunting technologies, including dart shaft design, wood selection, and point styles. Of particular interest is the description of three different techniques for the construction of throwing darts and the observation of stability in the hunting technology employed in the study area over seven millennia. Radiocarbon chronologies indicate that this period of stability was followed by an abrupt technological replacement of the throwing dart by the bow and arrow after 1200 BP. © The Arctic Institute of North America.

Krebs C.J.,University of British Columbia | Reid D.,Wildlife Conservation Society | Kenney A.J.,University of British Columbia | Gilbert S.,Yukon College
Canadian Journal of Zoology | Year: 2011

We estimated population density of brown lemmings (Lemmus sibiricus (Kerr, 1792)), Greenland collared lemmings (Dicrostonyx groenlandicus (Traill, 1823)), and tundra voles (Microtus oeconomus (Pallas, 1776)) on Herschel Island from 2007 to 2010 by mark-recapture on three live-trapping areas. Limited data were also available from Komakuk Beach on the north Yukon coast. In contrast to most previous studies, brown and collared lemmings were partly out of phase. Brown lemmings on Herschel reached peak density in 2007-2008 and were low in 2009-2010, while collared lemmings were at peak density in 2007-2008 and again in 2010. Large adult male body size was characteristic of peak populations. Brown lemmings increased dramatically in the peak summer of 2008 and collared lemmings increased rapidly when winter breeding under the snow was successful in 2009-2010. By contrast, at Komakuk Beach, we could see no clear signs of fluctuations in these three species. Winter snow conditions may be too severe for population persistence on the coastal plain along the north coast of the Yukon. Further work is needed to unravel why peak lemming densities are so variable among sites and why lemming fluctuations are so pronounced on the arctic coastal plain of Alaska and virtually absent on the coastal plain of the north Yukon.

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