The effect of snow cover on lemming population cycles in the Canadian High Arctic

Rising temperatures and changes in the precipitation regime will have a strong impact on the quality of the snow cover in the Arctic. A snow cover of good quality protecting lemmings from cold temperatures and predators is thought to be an important factor for maintaining the cyclic dynamic of their populations in the tundra. We examined if the characteristics of annual fluctuations (amplitude and shape of phases) in brown lemming (Lemmus trimucronatus) density could be determined by snow depth, snow density, sub-nivean temperature and persistence of snow. Using an 18-year time series of brown lemming abundance on Bylot Island in the Canadian Arctic, we tested if snow variables could explain the residual variation between the observed lemming density and the one predicted by models where cyclicity had been accounted for. Our analysis provides support for the hypothesis that snow cover can affect the amplitude and possibly also the periodicity of lemming population cycles in the High Arctic. Summer abundance of brown lemmings was higher following winters with a deep snow cover and a low-density snow pack near the ground but was unaffected by the date of establishment or melting and duration of the snow cover. Two snow variables showed a temporal trend; mean winter snow depth tended to increase and date of establishment of the hiemal threshold occurred earlier over time. These temporal trends, which should be favourable to lemmings, may explain why healthy population cycles have apparently been maintained at our study site contrary to other Arctic sites.     

Projected Polar Bear Sea Ice Habitat in the Canadian Arctic Archipelago

Background

Sea ice across the Arctic is declining and altering physical characteristics of marine ecosystems. Polar bears (Ursus maritimus) have been identified as vulnerable to changes in sea ice conditions. We use sea ice projections for the Canadian Arctic Archipelago from 2006 – 2100 to gain insight into the conservation challenges for polar bears with respect to habitat loss using metrics developed from polar bear energetics modeling.

Principal Findings

Shifts away from multiyear ice to annual ice cover throughout the region, as well as lengthening ice-free periods, may become critical for polar bears before the end of the 21^st century with projected warming. Each polar bear population in the Archipelago may undergo 2–5 months of ice-free conditions, where no such conditions exist presently. We identify spatially and temporally explicit ice-free periods that extend beyond what polar bears require for nutritional and reproductive demands.

Conclusions/Significance

Under business-as-usual climate projections, polar bears may face starvation and reproductive failure across the entire Archipelago by the year 2100.     

Diatoms and their relationship to environmental variables from lakes and ponds on Bathurst Island, Nunavut, Canadian High Arctic

Baseline and historical environmental data are sparse in the High Arctic, however diatom assemblages preserved in high arctic lake and pond sediment profiles can provide proxy data of past environmental changes. Ecological data, however, are still sparse. Diatom taxa preserved in the surficial sediment of lakes and ponds on Bathurst Island (75° 42 N, 97° 21 W), Nunavut, Canadian High Arctic, and their relationship to 34 environmental variables were examined using multivariate statistics. A total of 148 diatom taxa were identified from the surface sediments of 29 study sites. Five environmental variables, Fe³⁺, Total Phosphorus (Unfiltered) (TPU), Total Nitrogen (TN), Temperature (TEMP) and pH significantly (P0.05) accounted for most of the variation in the diatom assemblages. TN was also significantly correlated to other variables (e.g. TPF, DOC, POC). A CCA constrained to TN indicated that this variable best explained the species distributions, and a weighted-averaging (WA) model was developed to infer nutrient levels from the relative abundances of the 58 dominant taxa. Interestingly, previous limnological work indicated that nitrogen most likely limited algal production in some of these high arctic sites. This model may be used to quantitatively estimate past TN levels from diatom assemblages preserved in sediment cores from Bathurst Island, and may provide a means to track past environmental changes in the High Arctic.     

Cytological and ultrastructural preservation in Eocene Metasequoia leaves from the Canadian High Arctic

The ultrastructural examination by transmission electron microscopy of 45-million-year-old mummified leaves of Metasequoia extracted from the Upper Coal member of the Buchanan Lake Formation in Napartulik on Axel Heiberg Island revealed the preservation of intact chloroplasts and chloroplast components. Abundant tanniferous cell inclusions may indicate that the 3-mo period of constant daylight during the Artic summer induced high concentrations of tannins in the leaf tissues, which may have arrested microbial degradation of the litter. Quantified differences in the extent of chloroplast preservation through a vertical section of the lignite suggest that short-term shifts in the depositional environment took place, perhaps influencing the exposure of the leaf tissues to conditions that would either promote or inhibit decomposition.     

Breeding biology and provisioning of nestling snow buntings in the Canadian High Arctic

We examined basic breeding biology, as well as the effects of parental sex, brood size, nestling age, and nest habitat on foraging distances and parental food delivery rates of snow buntings (Plectrophenax nivalis) on Devon Island, NT, Canada, in the summers of 2003–2006. Clutch sizes and initiation dates were similar to those found in previous studies, although nest density was much higher. Feeding rates and foraging distances of buntings differed depending on the size and age of the brood, but were similar between nest habitats. Unlike in earlier studies, we found that male buntings made fewer feeding visits, but traveled longer distances to forage for food than females. Whether these differences between the sexes relate to reducing competition for prey, or to differing sex roles in parental care due to the poorly insulated nest cavities of this species, remains to be determined.     

Carbon sources for lake food webs in the Canadian High Arctic and other regions of Arctic North America

We investigated the role of autochthonous and terrestrial carbon in supporting aquatic food webs in the Canadian High Arctic by determining the diet of the dominant primary consumer, aquatic chironomids. These organisms were studied in fresh waters on 3 islands of the Arctic Archipelago (~74–76°N) including barren polar desert watersheds and a polar oasis with lush meadows. Stomach content analysis of 578 larvae indicated that chironomids primarily ingested diatoms and sediment detritus with little variation among most genera. Carbon and nitrogen stable isotope mixing models applied to 2 lakes indicated that benthic algae contributed 68–95% to chironomid diet at a polar desert site and 70–78% at a polar oasis site. Detritus, originating from either phytoplankton or terrestrial sources, also contributed minor amounts to chironomid diet (0–32%). Radiocarbon measurements for the 2 lakes showed that old terrestrial carbon did not support chironomid production. Carbon stable isotope ratios of chironomids in other High Arctic lakes provided further dietary evidence that was consistent with mixing model results. These findings indicate that, in the Canadian High Arctic, chironomids (and fish that consume them) are supported primarily by benthic algae in both polar desert and oasis lakes. In contrast, our review of carbon flow studies for lakes in other Arctic regions of North America shows that terrestrial carbon and phytoplankton can be important energy sources for consumers. This study provides a baseline to detect future climate-related impacts on carbon pathways in High Arctic lakes.     

Environmental influences on the structure of sedge meadows in the Canadian High Arctic

Wet sedge-dominated communities (sedge meadows) were sampled in five lowland oases in the Queen Elizabeth Islands of the Canadian High Arctic to assess species-environment relationships. The sites spanned 4° of latitude, and varied in lithology and intensity of grazing by muskoxen (Ovibos moschatus). A suite of 8 vascular species were common in all meadow stands, with an additional 4–6 species found in most stands. The position of these species in dominance-diversity curves was not significantly different between grazed and ungrazed meadows however, the grazed sites appeared to follow a log-normal distribution, while the ungrazed sites were more geometric. Redundancy analysis indicated that grazing intensity is important in determining structure in arctic sedge meadows, largely through increasing the cover of bryophytes and the availability of nitrogen. Greatest species richness was found in the more southerly sites which were moderately grazed and had diversity in microtopography. Abbreviations: AF – Alexandra Fiord, PBP – Polar Bear Pass, PMB – Princess Marie Bay, TL – Truelove Lowland, SP – Sverdrup Pass Nomenclature: Porsild, A.E. & Cody, W.J. 1980. Vascular plants of continental Northwest Territories. National Museums of Canada, Ottawa.     

Dive form and function in belugas Delphinapterus leucas of the eastern Canadian High Arctic

The underwater behaviour of 11 belugas or white whales was examined during summer using time-at-depth records relayed by satellite-linked data-loggers. Simultaneous tracking information was obtained for each whale. Eight distinct dive profiles were identified in submergences made to depths of >40 m. Four of these, together comprising 84% of these “deep” dives, were of a square profile. They were characterised by a continuous descent to a particular depth (usually the sea bed), a “bottom phase” at or near that depth, and a direct ascent to the surface. These dives are presumed to be made for benthic foraging. Other, much less common, dive shapes were “V”-shaped, parabolic and trapezoidal. “Shallow” dives (15–40 m depth) were of a variety of shapes, short duration and high average horizontal speeds. Many probably occurred during periods of directed travel. This population of belugas treats most of the water column as dead space separating resources of oxygen and nutrition. Received: 8 January 1998 / Accepted: 27 April 1998     

Impacts of warming and fertilization on nitrogen-fixing microbial communities in the Canadian High Arctic

The impacts of simulated climate change (warming and fertilization treatments) on diazotroph community structure and activity were investigated at Alexandra Fiord, Ellesmere Island, Canada. Open Top Chambers, which increased growing season temperatures by 1-3 degrees C, were randomly placed in a dwarf-shrub and cushion-plant dominated mesic tundra site in 1995. In 2000 and 2001 20N:20P2O5:20K2O fertilizer was applied at a rate of 5 gm(-2) year(-1). Estimates of nitrogen fixation rates were made in the field by acetylene reduction assays (ARA). Higher rates of N fixation were observed 19-35 days post-fertilization but were otherwise unaffected by treatments. However, moss cover was significantly positively associated with ARA rate. NifH gene variants were amplified from bulk soil DNA and analyzed by terminal restriction fragment length polymorphism analysis. Non-metric multidimensional scaling was used to ordinate treatment plots in nifH genotype space. NifH gene communities were more strongly structured by the warming treatment late in the growing season, suggesting that an annual succession in diazotroph community composition occurs.     

High Bacterial Diversity of Biological Soil Crusts in Water Tracks over Permafrost in the High Arctic Polar Desert

In this study we report the bacterial diversity of biological soil crusts (biocrusts) inhabiting polar desert soils at the northern land limit of the Arctic polar region (83° 05 N). Employing pyrosequencing of bacterial 16S rRNA genes this study demonstrated that these biocrusts harbor diverse bacterial communities, often as diverse as temperate latitude communities. The effect of wetting pulses on the composition of communities was also determined by collecting samples from soils outside and inside of permafrost water tracks, hill slope flow paths that drain permafrost-affected soils. The intermittent flow regime in the water tracks was correlated with altered relative abundance of phylum level taxonomic bins in the bacterial communities, but the alterations varied between individual sampling sites. Bacteria related to the Cyanobacteria and Acidobacteria demonstrated shifts in relative abundance based on their location either inside or outside of the water tracks. Among cyanobacterial sequences, the proportion of sequences belonging to the family Oscillatoriales consistently increased in relative abundance in the samples from inside the water tracks compared to those outside. Acidobacteria showed responses to wetting pulses in the water tracks, increasing in abundance at one site and decreasing at the other two sites. Subdivision 4 acidobacterial sequences tended to follow the trends in the total Acidobacteria relative abundance, suggesting these organisms were largely responsible for the changes observed in the Acidobacteria. Taken together, these data suggest that the bacterial communities of these high latitude polar biocrusts are diverse but do not show a consensus response to intermittent flow in water tracks over high Arctic permafrost.     

Birth Order, Age, and Hunting Success in the Canadian Arctic

What explains variation in hunting success? This paper examines foraging success among Inuit hunters, paying particular attention to factors that account for differential returns in hunting. Although there are several possibilities for explaining hunting success, this study finds that birth order and age are important predictors of foraging returns. Furthermore, data on food sharing suggests that birth order has important effects on the distribution of food. That is, early-born hunters not only produce more food, they give much of that food to their parents, who then distribute it to the hunter’s younger siblings. These findings are discussed within the context of local resource enhancement and the value of early-born sons to Inuit parents.     

Greater nitrogen and/or phosphorus availability increase plant species’ cover and diversity at a High Arctic polar semidesert

Enhanced nitrogen (N) deposition at high latitudes is a circumpolar phenomenon. Low soil phosphorus (P), however, may limit vegetation responses to increased N inputs. From 2000 to 2002, the effects of N at 0, 0.5 (a rate occurring in Greenland and Iceland) and 5 (equivalent to deposition in areas of Europe) g N m⁻² a⁻¹ and P (0.1 g m⁻² a⁻¹) treatments on plant species’ cover and diversity were determined at a polar semidesert site (ambient deposition c 0.1 g N m⁻² a⁻¹) in Svalbard (79°N). The largest response was to combined 5 g N plus 1 g P m⁻² a⁻¹, where cover of Saxifraga oppositifolia increased c fourfold, density of Salix polaris leaves c ninefold, seedlings of several ‘new’ species (Draba oxycarpa, Saxifraga caespitosa, Sagina nivalis) were established and ‘immigration’ of Bryum arcticum and ‘extinction’ of Schistidium apocarpum were observed. There were fewer, less pronounced, effects on the plant community at 0.5 g N m⁻² a⁻¹. Low P availability did indeed appear to restrict vegetation response to N. There was a trend for plant species’ richness and diversity to increase with 1 g P m⁻² a⁻¹ at 0 and 0.5 g N m⁻² a⁻¹, but not at 5 g N m⁻². Plant species showed individualistic responses so that generalisation by functional type was not possible. Such increased colonisation by moss species of bare soil, and greater densities of previously unrecorded angiosperm seedlings, are not usually observed in more closed (subarctic) tundra as a response to N and P additions. These changes are likely to influence significantly nutrient cycles, whole system carbon budgets and surface energy and water balances. Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users.     

Mitochondrial DNA diversity in an apomictic Daphnia complex from the Canadian High Arctic

Cyclic parthenogenesis is the ancestral mode of reproduction in the cladoceran crustacean, Daphnia pulex, but some populations have made the transition to obligate parthenogenesis and this is the only mode of reproduction known to occur in arctic populations. Melanism and polyploidy are also common in arctic populations of this species. Prior allozyme studies of arctic D. pulex revealed substantial levels of clonal diversity on a regional scale. Clonal groupings based on cluster analysis of allozyme genotypes do not conform to groupings based on the presence/absence of melanin or on ploidy level. In order to further elucidate genetic relationships among arctic D. pulex clones, mitochondrial DNA (mtDNA) variation was examined in 31 populations from two Canadian high-arctic sites. The data were also compared to a previous study of mtDNA variation in populations from a Canadian low-arctic site. Cladistic analysis of restriction site variation of the entire mitochondrial genome and nucleotide sequence variation of the mitochondrial control region was used to construct genetic relationships among mitochondrial genotypes. Three distinct mitochondrial lineages were detected. One lineage was associated with diploid, nonmelanic clones and is the same as the lineage that is found in temperate populations of D. pulex. The other two lineages (A & B) were associated with polyploid, melanic clones. Sequence divergence between the A and B lineages was 2.4%. Sequence divergence between D. pulex and either of these two lineages exceeded 3%. It is suggested that the melanic, polyploid clones are hybrids between males of D. pulex (and/or a closely related congener, D. pulicaria) and females of either of two ancestral melanic species that have mitochondrial lineages A and B. Geographic patterns of mitochondrial diversity in ‘melanic’ lineage B support the hypothesis of an high-arctic refuge for the ancestral species during the last glacial period.     

Nitrogen fixation by three species of leguminosae in the Canadian High Arctic Tundra

Abstract. Significant levels of nitrogenase activity (nitrogen fixation) were demonstrated in three species of Arctic legumes ( Oxytropis maydelliana, O. arctobia and Astragalus alpinus ) growing in high tundra at Sarcpa Lake, Melville Peninsula, N.W.T. Nitrogenase activity of intact plants was correlated with the number of nodules per plant, with field soil temperatures and limited by water shortage. Activity in freshly detached nodules showed a plateau of maximum activity between 10°C and 25°C and a near linear decline with temperature down to 0°C. Unusually, the segmented nodules of all three species are perennial in which growth and leghaemoglobin production resumes each spring from an overwintering apical meristem. Nodules are most numerous in the warmer soil stratum (2–10 cm. depth). Other studies indicate that the arctic rhizobia belong to a single cold-adapted species which has co-evolved with the legumes of tundra.     

Seasonal and annual variability in the quality of important forage plants on Banks Island,Canadian High Arctic

Abstract. In vitro acid‐pepsin digestibility (IVDMD), crude protein (CP), fibre, lignin, and energy content were measured for a variety of forage plants collected annually from Banks Island over five summers and three winters from 1993–1998. Summer samples were collected during mid‐June (start of growing season), mid‐July (peak of growing season), and mid‐late August (senescence). Winter samples were collected in early (November), mid‐ (February), and late‐ (April/May) winter. Samples, collected in areas of both high and low muskox density, included Carex aquatilis, unidentified Carex, Salixarctica, Dryasintegrifolia, Cassiope tetragona, Saxifraga spp., Astragalus spp., Oxytropis spp., lichen, and grass. Seasonal dynamics in forage quality during the growing season were similar to those reported elsewhere in the arctic and high arctic and were consistent across years. However, there were significant year effects in lignin, fibre, and energy content of forages and the crude protein (CP) content of C. aquatilis in winter, indicating annual differences in the quality of forage available to herbivores. The quality of forages on Banks Island was similar between areas subjected to different densities of muskox (ca. 1.6–1.9 versus 0.3 ‐ 0.4/km²) implying that quality was not affected by these grazing intensities. The Banks Island high arctic ecosystem supports an abundance of herbivores. It has been hypothesized that this is because forage quality and/or quantity are superior on Banks Island than elsewhere in the high arctic. Our results regarding forage quality are equivocal. Although the maximum CP content of forages from Banks Island was generally higher than reported elsewhere in the arctic and high arctic, CP content reported elsewhere fell within the interannual range reported from Banks Island. Fibre and energy content of forages from Banks Island were similar to slightly lower than elsewhere in the arctic and high arctic. Such comparisons must be considered in light of the interannual variability in quality we report.     

Phenological and growth responses of Papaver radicatum along altitudinal gradients in the Canadian High Arctic

Phenology and growth of Papaver radicatum Rottb. was monitored over four summers (1990–1993) at 12 sites, along a dolomitic and a granitic altitudinal gradient (330 m a.s.l.–770 m a.s.l.) at Sverdrup Pass, central Ellesmere Island, Canada. The gradients provided substantial differences in environmental characteristics. Three of the four seasons (1990, 1991 and 1993) had more than 400 thawing degree-days (TDD) in the valley, while the 1992 season had less than 300. The granitic sites had consistently higher temperatures than the dolomitic sites, despite their northerly aspect. Increasing elevation reduced total degree-day accumulation ( c . 40 degree-days/100 m) and length of potential growing season. The proportion of the population producing flower buds was similar at all sites in any given year, but there were differences among years. Production of flowers and fruits per site, decreased with altitude along the dolomitic gradient in 1991 and 1992. There was no difference in the number of buds or flowers produced per plant with increasing altitude, although larger plants with multiple flowers were found only on low elevation granitic sites. Plants from the dolomitic sites were smaller and flowered, on average, after the site accumulated 150 degree-days, while plants on the granitic sites were larger and bloomed after 200 degree-days. Papaver is able to grow and reproduce over a wide range of environmental conditions and moderate climate warming would likely promote its growth and establishment, unless other factors, especially snow-free periods and water availability, become limiting.     

Note on sea-ice nematodes (Monhysteroidea) from Resolute Passage, Canadian High Arctic

Nematodes from the bottom section of first-year ice sampled every 4 days during April/May 1992 at two adjacent sites of an ice field station in Resolute Passage have been identified as members of the Monhysteroidea: Theristus melnikovi Tchesunov, 1986; Cryonema tenue Tchesunov and Riemann, 1995; and three unknown monhysterids that are similar to Cryonema. The maximum population density of nematodes was 23 810 m⁻². None of the ice nematodes has ever been reported from benthic samples and their occurrence in ephemeral sea ice is the subject of hypotheses. Since a drastic change of the community structure was noted to take place within a few days, it is assumed that the majority of ice-nematode species do not represent an autochthonous faunal element in the examined habitat and that the main site for their reproduction is elsewhere. The nematode community found near the undersurface of ephemeral ice is apparently influenced by particular import and export processes that are unknown as yet. Received: 2 October 1996 / Accepted: 15 December 1996     

Birth seasonality,photoperiod, and social change in the Central Canadian Arctic

Birth seasonally at high latitudes is a complex phenomenon which is undoubtedly affected by a subtle interaction between environmental rhythmicity (most notably in photoperiod and temperature) and cultural adaption. There is intriguing evidence that human gonadotrophic activity (and hence fertility) may be affected by seasonal fluctuations in light intensity and duration. Nevertheless, cultural factors are important insofar as they mediate between environmental rhythmicity and human fertility/birth patterns. This article examines the distribution of births over several decades in an Inuit community located 300 miles north of the Arctic Circle. Several shifts in birth seasonality are noted, the most significant of which is a dramatic shift from pronounced seasonality in the 1970s to non-seasonality in the 1980s. Longitudinal ethnographic fieldwork has allowed an examination of social and economic changes accounting for the rather sudden disappearance of birth seasonality. These include increasing reliance upon wage employment and social assistance, decreased dependence upon subsistence hunting and trapping, changing attitudes on the part of young people entering their prime reproductive years, and the introduction of television, radio, and southern-style recreational activities.