100 research outputs found
Evidence of Recent Treeline Dynamics in Southwest Yukon from Aerial Photographs
Small-scale vertical aerial photographs taken in 1947 and 1948 covering 200 km2 of the Kluane Ranges, southwest Yukon, were compared with corresponding photographs taken in 1989 for the purpose of characterizing changes in the distribution and abundance of white spruce (Picea glauca (Moench) Voss) at the alpine treeline. Digital photogrammetry, including orthorectification and on-screen interpretation, was supplemented by stereoscopic inspection of the original prints. Qualitative assessment of change across nine image pairs was accompanied by quantitative analysis of changes in spruce density and elevation using 1 hectare plots and 100 m wide elevational belt transects, respectively, superimposed on the orthorectified images. Significant changes were observed over the 41 years, but the degree of change varied throughout the study area. The most common changes were an increase in canopy size of individual trees and an increase in stand density resulting from the establishment of new individuals. Several instances of treeline advance were also observed. An absence of major natural disturbances or widespread land use change indicates that treeline change is attributable to climate. Results from concurrent dendroecological studies indicate that these dynamics represent only part of the total extent of change to occur during the 20th century.Des photographies aĂ©riennes verticales Ă petite Ă©chelle prises en 1947 et 1948 sur une aire de 200 km2 de la chaĂźne de montagnes Kluane, dans le sud-ouest du Yukon, ont Ă©tĂ© comparĂ©es Ă des photos correspondantes prises en 1989 dans le but de caractĂ©riser les changements en matiĂšre de rĂ©partition et dâabondance de lâĂ©pinette blanche (Picea glauca (Moench) Voss) Ă la hauteur de la limite alpine des arbres. La photogrammĂ©trie numĂ©rique, dont les techniques de redressement diffĂ©rentiel et dâinterprĂ©tation Ă lâĂ©cran, a Ă©tĂ© supplĂ©mentĂ©e par lâinspection stĂ©rĂ©oscopique des Ă©preuves photographiques originales. LâĂ©valuation qualitative du changement par rapport Ă neuf paires dâimages sâest accompagnĂ©e de lâanalyse quantitative des changements en matiĂšre de densitĂ© des Ă©pinettes et dâĂ©lĂ©vation Ă lâaide de parcelles de 1 hectare et de transects dâĂ©lĂ©vation en bandes de 100 m de large, respectivement, superposĂ©s sur les images ayant fait lâobjet du redressement diffĂ©rentiel. Dâimportants changements ont Ă©tĂ© observĂ©s au cours de la pĂ©riode de 41 ans, mais le degrĂ© de changement variait dâun endroit Ă lâautre visĂ© par lâĂ©tude. Les changements les plus courants consistaient en lâaugmentation de la taille du couvert des arbres individuels ainsi quâen lâaugmentation de la densitĂ© de peuplement dĂ©coulant de lâĂ©tablissement de nouveaux individus. Plusieurs occurrences dâavancement de la limite des arbres ont Ă©galement Ă©tĂ© observĂ©es. Lâabsence de perturbations naturelles majeures ou dâimportants changements sur le plan de lâutilisation des terres laisse croire que le changement de la limite des arbres est attribuable au climat. Les rĂ©sultats dĂ©coulant dâĂ©tudes dendroĂ©cologiques concurrentes indiquent que ces dynamiques ne reprĂ©sentent quâune partie de lâampleur totale du changement sâĂ©tant produit au cours du XXe siĂšcle
Does seasonal variation in forage quality influence the potential for resource competition between muskoxen and Peary caribou on Banks Island?
Inter- and intra-annual variation in forage quality may influence population dynamics of Peary caribou and muskoxen on Banks Island. From 1993 to 1998 we collected 300 composite samples of sedge (Carex aquatilis and Carex spp.), willow (Salix arctica), legume (Oxytropis spp. and Astragalus spp.), and avens (Dryas integrifolia). Samples were collected in mid-June (start of the growing season), mid-July (peak of the growing season), mid-late August (senescence), and early (November), mid- (February), and late- (April/May) winter. We analysed forages for percent digestibility (in vitro acid-pepsin dry matter digestibility), crude protein (CP), fibre, lignin, and energy content. There was significant inter-annual variation in levels of lignin, fibre, and energy, and significant intra-annual (seasonal) variation for all quality measures and forages, which reflected the strong difference in quality between summer and winter. We discuss the relationship between forage quality and seasonal diet composition of Peary caribou and muskoxen, and the potential implications for the reduced Peary caribou and high muskoxen populations
Adaptations of a native Subantarctic flightless fly to dehydration stress: more plastic than we thought? ( Short Communication)
Water conservation is a critical aspect affecting the survival, distribution and abundance of terrestrial arthropods. In this study we investigate mechanisms of dehydration tolerance of the native, flightless fly, Calycopteryx moseleyi, inhabiting contrasting environments at two localities in the Kerguelen Islands. We compare the survival abilities and management of body water content of adult flies from two different ecophenotypes when exposed to conditions of low relative humidity. Our results suggest a broad plasticity in the responses of C. moseleyi to desiccation, showing distinct local adaptations to environmental conditions
Plant interactions are unimportant in a subarctic-alpine plant community
We investigated whether plant interaction intensity in a subarctic-alpine meadow is important for determining community structure and species abundance. Using two common species as phytometers, we measured interaction intensity using a neighbor removal approach. Eight biotic and abiotic variables known to influence species abundance and community structure were measured, with regression trees used to examine how plant interactions and the biotic and abiotic variables were related to species evenness, richness, and phytometer spatial cover. A range of interactions was present, with both strong competition and facilitation present over small-scale abiotic and biotic gradients. Despite the variation in interaction intensity, it was generally unrelated to either community structure or phytometer cover. In other words, plant interactions were intense in many cases but were not important to community structure. This may be due to the prevalence of clonal species in this system and the influence of previous year's interactions on plant survival and patterns of community structure. These results also suggest how conflicting theories of the role of competition in unproductive environments may be resolved. Our findings suggest that plant interactions may be intense in reducing individual growth, while simultaneously not important in the context of community structure. Plant interactions need to be viewed and tested relative to other factors and stresses to accurately evaluate their importance in plant communities, with continued differentiation between the intensity of plant interactions and their relative importance in communities
Wolf Reproduction in Response to Caribou Migration and Industrial Development on the Central Barrens of Mainland Canada
Reproductive success of mammals is greatly influenced by food availability. Where wolves (Canis lupus) prey on migratory barren-ground caribou (Rangifer tarandus), caribou migration patterns strongly influence food availability for wolves. However, industrial development in formerly undeveloped wolf range could also negatively influence wolf reproduction, either directly (by disrupting normal feeding behavior) or indirectly (by impacting caribou migrations). We used a cross-sectional timeseries regression to analyze eight years of wolf reproductive data with respect to spatial and temporal variation in caribou migration and economic development in a 49 900 km2 area of the Northwest Territories, Canada. Reproductive success decreased as the distance from wolf dens to caribou migration routes increased, while the timing of caribou migrations had little effect. There was no measurable effect of current levels of economic development on reproductive success, although evidence suggests the potential for indirect effects. Continued monitoring is required to identify possible thresholds of adverse effects for wolf populations.La rĂ©ussite de reproduction des mammifĂšres dĂ©pend beaucoup de la disponibilitĂ© de la nourriture. LĂ oĂč les loups (Canis lupus) ont comme proie le caribou de la toundra en migration (Rangifer tarandus), le schĂ©ma des migrations du caribou joue un grand rĂŽle sur la disponibilitĂ© de nourriture des loups. Cela dit, lâexpansion industrielle dans dâanciennes aires de rĂ©partition non amĂ©nagĂ©es du loup pourrait aussi avoir une influence nĂ©gative sur la reproduction du loup, directement (perturbation du comportement dâalimentation habituel) ou indirectement (impact sur la migration du caribou). Nous avons recouru Ă une rĂ©gression chronologique transversale pour analyser huit annĂ©es de donnĂ©es de reproduction du loup par rapport Ă la variation spatiale et temporelle de la migration du caribou et au dĂ©veloppement Ă©conomique dans une zone de 49 900 km2 des territoires du Nord-Ouest, au Canada. La rĂ©ussite de reproduction diminuait au fur et Ă mesure que la distance entre les taniĂšres de loups et les routes de migration du caribou augmentaient, tandis que le moment choisi pour les migrations du caribou avait peu dâeffets. Le dĂ©veloppement Ă©conomique actuel nâavait aucun effet mesurable sur la rĂ©ussite de reproduction, bien que certains indices laissent croire quâil pourrait avoir des effets indirects. Il y a donc lieu dâeffectuer une surveillance continue afin de dĂ©terminer les seuils possibles dâeffets nuisibles sur les populations de loups
Influence of Shrub Canopies on Growth Rate and Pre-Hibernation Mass of Juvenile Arctic Ground Squirrels
The wide-spread encroachment of canopy-forming shrubs into northern and alpine tundra communities is likely to alter many plantâanimal interactions, with direct and indirect impacts on herbivore populations. Specifically, shrub encroachment may impact habitat quality for herbivores by changing predation risk as a result of reduced visibility. We investigated the association between visibility and growth of juvenile arctic ground squirrels Urocitellus parryii across an alpine tundra ecotone with varying shrub cover. Marked individuals were weighed throughout the period following emergence from natal burrows in early summer until just prior to hibernation. Both males and females showed a positive association between habitat-specific visibility and post-emergence growth rate. There was a positive relationship between post-emergence juvenile growth rate and pre-hibernation mass for females but not males. As shrubs increase, ground squirrel populations may be adversely affected by reductions in habitat-scale visibility
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