Barren‐ground caribou (Rangifer tarandus groenlandicus) behaviour after recent fire events; integrating caribou telemetry data with Landsat fire detection techniques

Fire regimes are changing throughout the North American boreal forest in complex ways. Fire is also a major factor governing access to high‐quality forage such as terricholous lichens for barren‐ground caribou (Rangifer tarandus groenlandicus). Additionally, fire alters forest structure which can affect barren‐ground caribou's ability to navigate in a landscape. Here, we characterize how the size and severity of fires are changing across five barren‐ground caribou herd ranges in the Northwest Territories and Nunavut, Canada. Additionally, we demonstrate how time since fire, fire severity, and season result in complex changes in caribou behavioural metrics estimated using telemetry data. Fire disturbances were identified using novel gap‐free Landsat surface reflectance composites from 1985 to 2011 across all herd ranges. Burn severity was estimated using the differenced normalized burn ratio. Annual area burned and burn severity were assessed through time for each herd and related to two behavioural metrics: velocity and relative turning angle. Neither annual area burned nor burn severity displayed any temporal trend within the study period. However, certain herds, such as the Ahiak/Beverly, have more exposure to fire than other herds (i.e. Cape Bathurst had a maximum forested area burned of less than 4 km²). Time since fire and burn severity both significantly affected velocity and relative turning angles. During fall, winter, and spring, fire virtually eliminated foraging‐focused behaviour for all 26 years of analysis while more severe fires resulted in a marked increase in movement‐focused behaviour compared to unburnt patches. Between seasons, caribou used burned areas as early as 1‐year postfire, demonstrating complex, nonlinear reactions to time since fire, fire severity, and season. In all cases, increases in movement‐focused behaviour were detected postfire. We conclude that changes in caribou behaviour immediately postfire are primarily driven by changes in forest structure rather than changes in terricholous lichen availability.     

Climate-Driven Effects of Fire on Winter Habitat for Caribou in the Alaskan-Yukon Arctic

Climatic warming has direct implications for fire-dominated disturbance patterns in northern ecosystems. A transforming wildfire regime is altering plant composition and successional patterns, thus affecting the distribution and potentially the abundance of large herbivores. Caribou (Rangifer tarandus) are an important subsistence resource for communities throughout the north and a species that depends on terrestrial lichen in late-successional forests and tundra systems. Projected increases in area burned and reductions in stand ages may reduce lichen availability within caribou winter ranges. Sufficient reductions in lichen abundance could alter the capacity of these areas to support caribou populations. To assess the potential role of a changing fire regime on winter habitat for caribou, we used a simulation modeling platform, two global circulation models (GCMs), and a moderate emissions scenario to project annual fire characteristics and the resulting abundance of lichen-producing vegetation types (i.e., spruce forests and tundra >60 years old) across a modeling domain that encompassed the winter ranges of the Central Arctic and Porcupine caribou herds in the Alaskan-Yukon Arctic. Fires were less numerous and smaller in tundra compared to spruce habitats throughout the 90-year projection for both GCMs. Given the more likely climate trajectory, we projected that the Porcupine caribou herd, which winters primarily in the boreal forest, could be expected to experience a greater reduction in lichen-producing winter habitats (−21%) than the Central Arctic herd that wintered primarily in the arctic tundra (−11%). Our results suggest that caribou herds wintering in boreal forest will undergo fire-driven reductions in lichen-producing habitats that will, at a minimum, alter their distribution. Range shifts of caribou resulting from fire-driven changes to winter habitat may diminish access to caribou for rural communities that reside in fire-prone areas.     

Interchange and Overlap Among Four Adjacent Arctic Caribou Herds

Barren ground caribou (Rangifer tarandus granti) are distributed in herds that seasonally use specific geographic regions within an annual range, with varying levels of fidelity during different periods (e.g., calving, insect relief, wintering). As a result, caribou management is generally tailored to individual herds that often range across administrative boundaries. Herd ranges can shift over time, seasonal ranges of adjacent herds often overlap, herds merge, and there is often little genetic differentiation among adjacent herds. If substantial herd interchange occurs, it would have important management implications by influencing estimates of herd size, herd composition, and harvest rates. We compiled satellite telemetry data from 2003–2015 for 4 large arctic caribou herds to quantify herd interchange rates. We calculated a metric of herd interchange based on the relationship of caribou locations to typical weekly herd ranges (all yrs combined) and the distance to other radio-collared caribou from each of the 4 herds (yr specific). Although herd membership cannot always be clearly defined based on location, this metric provides an objective measure of the strength of evidence of herd membership that can be used to make comparisons among herds and time periods. We also calculated herd overlap and quantified how it varied throughout the year. Herd interchange was rare in the 2 larger herds, generally occurring when caribou overwintered with an adjacent herd, whereas herd interchange from the 2 smaller herds was more frequent and could last longer than a year. Although sample sizes were limited, there were no clear patterns in herd interchange with year or annual herd size. The 2 smaller herds had large seasonal overlap with adjacent herds, suggesting that herd interchange may be related to spatiotemporal herd overlap and relative herd size. Our results can help managers understand herd interchange and overlap to make management decisions, interpret research results, and develop more accurate population models. © 2020 The Authors. The Journal of Wildlife Management published by Wiley Periodicals LLC on behalf of The Wildlife Society.     

Population structure of caribou in an ice‐bound archipelago

Aim

Archipelagos provide ideal natural systems for testing the effects of isolation and fragmentation of habitats on the genetic makeup of populations—an important consideration, given that many insular species are of conservation concern. Two theories predominate: Island Biogeography Theory (IBT) posits that proximity to the mainland drives the potential for migrants and gene flow. The Central Marginal Hypothesis (CMH) predicts that island populations at the periphery of a species range may experience low gene flow, small population size and high rates of genetic drift. We investigated population genetic structure, genetic diversity and key drivers of diversity for Arctic island‐dwelling caribou (Rangifer tarandus). Our aim was to inform intraspecific units for conservation and decipher how IBT and CMH could act in an archipelago where isolation is highly variable due to sea ice and open water.

Location

Canadian Arctic Archipelago, Canada (Latitude, 55–82°N; Longitude, 61–123°W).

Methods

We genotyped 447 caribou at 16 microsatellite loci; these caribou represented two subspecies (R. t. groenlandicus, R. t. pearyi) and three designatable units. We used hierarchical Bayesian clustering and ordination to determine genetic groups. We evaluated the influence of ecological and geographic variables on genetic diversity using linear mixed‐effects models and compared diversity among mainland and island herds.

Results

Bayesian clustering revealed nine genetic clusters with differentiation among and within caribou subspecies. Genetic differentiation was explained predominantly by isolation‐by‐distance across all caribou, even at the scale of subspecies. Island caribou were less genetically diverse than mainland herds; individual heterozygosity was negatively correlated with distance‐to‐mainland and the extent of autumn ice‐free coastline and positively correlated with unglaciated island size.

Main conclusions

Our findings underscore the importance of hierarchical analysis when investigating genetic population structure. Genetic diversity and its key drivers lend support to both IBT and CMH and highlight the pending threat of climate change for Arctic island caribou.

     

How landscape dynamics link individual‐ to population‐level movement patterns: a multispecies comparison of ungulate relocation data

Aim To demonstrate how the interrelations of individual movements form large‐scale population‐level movement patterns and how these patterns are associated with the underlying landscape dynamics by comparing ungulate movements across species. Locations Arctic tundra in Alaska and Canada, temperate forests in Massachusetts, Patagonian Steppes in Argentina, Eastern Steppes in Mongolia. Methods We used relocation data from four ungulate species (barren‐ground caribou, Mongolian gazelle, guanaco and moose) to examine individual movements and the interrelation of movements among individuals. We applied and developed a suite of spatial metrics that measure variation in movement among individuals as population dispersion, movement coordination and realized mobility. Taken together, these metrics allowed us to quantify and distinguish among different large‐scale population‐level movement patterns such as migration, range residency and nomadism. We then related the population‐level movement patterns to the underlying landscape vegetation dynamics via long‐term remote sensing measurements of the temporal variability, spatial variability and unpredictability of vegetation productivity. Results Moose, which remained in sedentary home ranges, and guanacos, which were partially migratory, exhibited relatively short annual movements associated with landscapes having very little broad‐scale variability in vegetation. Caribou and gazelle performed extreme long‐distance movements that were associated with broad‐scale variability in vegetation productivity during the peak of the growing season. Caribou exhibited regular seasonal migration in which individuals were clustered for most of the year and exhibited coordinated movements. In contrast, gazelle were nomadic, as individuals were independently distributed and moved in an uncoordinated manner that relates to the comparatively unpredictable (yet broad‐scale) vegetation dynamics of their landscape. Main conclusions We show how broad‐scale landscape unpredictability may lead to nomadism, an understudied type of long‐distance movement. In contrast to classical migration where landscapes may vary at broad scales but in a predictable manner, long‐distance movements of nomadic individuals are uncoordinated and independent from other such individuals. Landscapes with little broad‐scale variability in vegetation productivity feature smaller‐scale movements and allow for range residency. Nomadism requires distinct integrative conservation strategies that facilitate long‐distance movements across the entire landscape and are not limited to certain migration corridors.     

The Circumpolar Arctic vegetation map

Abstract. Question: What are the major vegetation units in the Arctic, what is their composition, and how are they distributed among major bioclimate subzones and countries? Location: The Arctic tundra region, north of the tree line. Methods: A photo‐interpretive approach was used to delineate the vegetation onto an Advanced Very High Resolution Radiometer (AVHRR) base image. Mapping experts within nine Arctic regions prepared draft maps using geographic information technology (ArcInfo) of their portion of the Arctic, and these were later synthesized to make the final map. Area analysis of the map was done according to bioclimate subzones, and country. The integrated mapping procedures resulted in other maps of vegetation, topography, soils, landscapes, lake cover, substrate pH, and above‐ground biomass. Results: The final map was published at 1:7 500 000 scale map. Within the Arctic (total area = 7.11 × 106 km²), about 5.05 × 10⁶ km² is vegetated. The remainder is ice covered. The map legend generally portrays the zonal vegetation within each map polygon. About 26% of the vegetated area is erect shrublands, 18% peaty graminoid tundras, 13% mountain complexes, 12% barrens, 11% mineral graminoid tundras, 11% prostrate‐shrub tundras, and 7% wetlands. Canada has by far the most terrain in the High Arctic mostly associated with abundant barren types and prostrate dwarf‐shrub tundra, whereas Russia has the largest area in the Low Arctic, predominantly low‐shrub tundra. Conclusions: The CAVM is the first vegetation map of an entire global biome at a comparable resolution. The consistent treatment of the vegetation across the circumpolar Arctic, abundant ancillary material, and digital database should promote the application to numerous land‐use, and climate‐change applications and will make updating the map relatively easy.     

High genetic connectivity and introgression from domestic reindeer characterize northern Alaska caribou herds

Defining genetic populations and detecting hybridization with introduced or domestic taxa are two major concerns for the conservation of population-level diversity. We studied the genetic population structure of large, migratory caribou herds (Rangifer tarandus granti) on Alaska’s North Slope and their potential hybridization with introduced domestic reindeer (R. t. tarandus). Using a population genetics approach, we determined: (1) whether the four caribou herds could be differentiated; (2) how distance and population size appear to drive genetic population structure; and (3) how contact with reindeer has affected the genetic identity of herds. Samples from four caribou herds (n = 245) and reindeer (n = 67) were analyzed at 19 microsatellite loci. We found that North Slope caribou are isolated by distance, with no differentiation among herd pairs except for the most geographically distant herds (F _st  = 0.003, Jost’s D = 0.023; P-values < 0.001). We detected reindeer-caribou admixture in all populations except Kodiak Island, including 8 % of individuals in caribou herds and 14 % of individuals in Seward Peninsula reindeer herds. However, considering the stable or increasing trend in North Slope herds, reindeer introgression has had no apparent deleterious effect on herd demographics. Our findings indicate long-term genetic exchange among North Slope caribou herds when their ranges overlap, and suggest that herd size may influence susceptibility to reindeer introgression. As North Slope herd ranges are increasingly altered by industrial development, this study can provide a baseline for detecting potential future impacts to what are currently large, diverse, and naturally evolving herds.     

Evidence of alphaherpesvirus infections in Alaskan caribou and reindeer

Background  

The reindeer (Rangifer tarandus tarandus) industry in Alaska began with animals imported from Siberia (Russia) in the 1890's. Cervid herpes virus 2 (CvHV2) is endemic in reindeer in Scandinavia. We sought to determine if the same virus, or similar herpesviruses, were circulating in Alaskan reindeer and caribou (Rangifer tarandus granti). Serum samples from 292 reindeer were collected during annual reindeer handlings (1988-2005) near Nome, Alaska. In 2005, swab samples were collected from 40 calves from this herd, near Nome, Alaska. In 2007, ocular and nasal swab samples were collected from 30 apparently healthy reindeer calves near Wales, Alaska. Samples of plasma and white blood cells were collected from three Alaskan caribou herds, Mulchatna (n = 24), Teshekpuk (n = 34) and the Western Arctic (n = 87) in 2009.     

Prioritization of landscape connectivity for the conservation of Peary caribou

Adequate connectivity between discontinuous habitat patches is crucial for the persistence of metapopulations across space and time. Loss of landscape connectivity is often a direct result of fragmentation caused by human activities but also can be caused indirectly through anthropogenic climate change. Peary caribou (Rangifer tarandus pearyi) are widely dispersed across the islands of the Canadian Arctic Archipelago and rely on sea ice to move seasonally between island habitats throughout their range. Seasonal connectivity provided by sea ice is necessary to maintain genetic diversity and to facilitate dispersal and recolonization of areas from which caribou have been extirpated. We used least‐cost path analysis and circuit theory to model connectivity across Peary caribou range, and future climate projections to investigate how this connectivity might be affected by a warming climate. Further, we used measures of current flow centrality to estimate the role of High Arctic islands in maintaining connectivity between Peary caribou populations and to identify and prioritize those islands and linkages most important for conservation. Our results suggest that the Bathurst Island complex plays a critical role in facilitating connectivity between Peary caribou populations. Large islands, including Banks, Victoria, and Ellesmere have limited roles in connecting Peary caribou. Without rigorous greenhouse gas emission reductions our projections indicate that by 2100 all connectivity between the more southern Peary caribou populations will be lost for important spring and early‐winter movement periods. Continued connectivity across the Canadian Arctic Archipelago, and possibly Peary caribou persistence, ultimately hinges on global commitments to limit climate change. Our research highlights priority areas where, in addition to emission reductions, conservation efforts to maintain connectivity would be most effective.     

Impacts of climate change on the seasonal distribution of migratory caribou

Arctic ecosystems are especially vulnerable to global climate change as temperature and precipitation regimes are altered. An ecologically and socially highly important northern terrestrial species that may be impacted by climate change is the caribou, Rangifer tarandus . We predicted the current and potential future occurrence of two migratory herds of caribou [Rivière George herd (RG) and Rivière-aux-Feuilles (RAF) herd] under a Canadian General Circulation Model climate change scenario, across all seasons in the Québec–Labrador peninsula, using climatic and habitat predictor variables. Argos satellite-tracking collars have been deployed on 213 caribou between 1988 and 2003 with locations recorded every 4–5 days. In addition, we assembled a database of climate (temperature, precipitation, snowfall, timing and length of growing season) and habitat data obtained from the SPOT VEGETATION satellite sensor. Logistic regression models indicated that both climatic and physical habitat variables were significant predictors of current migratory caribou occurrence. Migratory caribou appeared to prefer regions with higher snowfall and lichen availability in the fall and winter. In the summer, caribou preferred cooler areas likely corresponding to a lower prevalence of insects, and they avoided disturbed and recently burnt areas. Climate change projections using climate data predicted an increased range for the RAF herd and decreased range for the RG herd during 2040–2069, limiting the herds to northeastern regions of the Québec–Labrador peninsula. Direct and indirect consequences of climate change on these migratory caribou herds possibly include alteration in habitat use, migration patterns, foraging behaviour, and demography, in addition to social and economic stress to arctic and subarctic native human populations.     

Caribou Distribution and Movements in a Northern Alaska Oilfield

As industrial development increases in the range of barren-ground caribou (Rangifer tarandus granti) across the warming Arctic, the need to understand the responses of caribou to development and to assess the effectiveness of mitigation measures increase accordingly. The Central Arctic Herd (CAH) of caribou ranges across northern Alaska, USA, and the herd's summer range includes the Prudhoe Bay and Kuparuk oilfields, where the herd has been exposed to oil development for >4 decades. We used location data from global positioning system (GPS) radio-collars deployed on female CAH caribou for 106 collar-years, recording locations every 2 hours during 2008–2019, to examine caribou distribution and movements during 7 different seasons of the year in relation to infrastructure in the Kuparuk oilfield, which is characterized by more design improvements and mitigation measures than the older Prudhoe Bay oilfield. We examined movement metrics in terms of distance to gravel infrastructure (roads and pads) and time before and after movements across infrastructure (crossings). We also employed integrated step-selection analysis to compare caribou movements with random movements. Caribou distribution was influenced by insect activity, distance to coast, landcover, and terrain ruggedness, and we found large seasonal differences in caribou responses to infrastructure. Consistent with previous research findings, avoidance of areas near roads and pads was strongest during the calving season and some caribou used roads and pads as insect-relief habitat when oestrid flies (warble fly [Hypoderma tarandi] and nose bot fly [Cephenemyia trompe]) were active. Caribou moved through the Kuparuk oilfield repeatedly during summer, averaging >2 road or pad crossings a day when harassment by mosquitoes (Aedes [Ochlerotatus] spp.) and oestrid flies were the predominant factors influencing caribou movements. Caribou moved faster while crossing roads and pads but showed little pattern in speed or turn angle with distance to roads and pads. These results demonstrate that the effects of petroleum development on a caribou herd with long-term exposure to industrial activity vary widely by season. Maternal caribou avoid active roads and pads during calving, but the incorporation of appropriate mitigation measures in oilfield design allows caribou to move through the Kuparuk oilfield during other snow-free seasons. © 2020 The Wildlife Society.     

Caribou (<Emphasis Type="Italic">Rangifer tarandus</Emphasis>) and Inuit Nutrition Security in Canada

Caribou (Rangifer tarandus) has been fundamental to the diet and culture of Arctic Indigenous Peoples for thousands of years. Although caribou populations observe natural cycles of abundance and scarcity, several caribou herds across the Circumpolar North have experienced dramatic declines in recent decades due to a range of interrelated factors. Broadly, the objectives of this study are to examine food and nutrition security in relation to wildlife population and management status across Inuit Nunangat (the Inuit homeland, consisting of four regions across the Canadian Arctic). Specifically, we: (1) characterize the contribution of caribou to Inuit nutrition across northern Canada and (2) evaluate the population and management status of caribou herds/populations harvested by Inuit. Dietary data were derived from the 2007–2008 Inuit Health Survey, which included dietary information for Inuit adults (n?=?2097) residing in thirty-six communities, spanning three regions (the Inuvialuit Settlement Region, Nunavut, and Nunatsiavut) of the Canadian North. Published information regarding the range, abundance, status, and management status of caribou herds/populations was collected through document analysis and was validated through consultation with northern wildlife experts (territorial governments, co-management, and/or Inuit organizations). While caribou contributed modestly to total diet energy (3–11% of intake) across the regions, it was the primary source of iron (14–37%), zinc (18–41%), copper (12–39%), riboflavin (15–39%), and vitamin B12 (27–52%), as well as a top source of protein (13–35%). Restrictions on Inuit subsistence harvest (harvest quotas or bans) are currently enacted on at least six northern caribou herds/populations with potential consequences for country food access for over twenty-five Inuit communities across Canada. A holistic multi-sectorial approach is needed to ensure the sustainability of wildlife populations, while supporting Inuit food and nutrition security in the interim.     

Shrub cover in northern Nunavik: can herbivores limit shrub expansion?

Recent climate changes have increased the primary productivity of many Arctic and subarctic regions. Erected shrub has been shown to increase in abundance over the last decades in northern regions in response to warmer climate. At the same time, caribou herds are declining throughout the circumboreal regions. Based on observation of heavy browsing on shrubs at Deception Bay (Nunavik, Canada), we hypothesized that the densification of shrubs observed in nearby locations did not occur at our study site despite of observed warming because of a recent peak of the Rivière-aux-Feuilles caribou herd. To assess shrub cover changes, we compared a 1972 mosaic of aerial photos to a 2010 satellite image over a 5 km² area, divided into 56 grids of 100 30 m × 30 m cells. Most cells (n = 4,502) did not show any changes in the cover of shrubs but those who did were as likely to increase as to decrease. The relative cover of shrubs in cells who changed was not higher in 2010 (6.1 ± 0.2 %) than in 1972 (7.3 ± 0.4 %). More than 70 % of birch and willow had more than 50 % of their shoot browsed, suggesting that caribou may limit shrub expansion at this site. We cannot rule out that abiotic factors also contribute to the inertia in shrub cover. Increases in shrub abundance reported in Nunavik and elsewhere were located closer to the tree line or in discontinuous permafrost, whereas our site is characterized by herbaceous arctic tundra, continuous permafrost and relatively low annual precipitation.     

Modern and ancient DNA reveal recent partial replacement of caribou in the southwest Yukon

The long‐term persistence of forest‐dwelling caribou (Rangifer tarandus caribou) will probably be determined by management and conservation decisions. Understanding the evolutionary relationships between modern caribou herds, and how these relationships have changed through time will provide key information for the design of appropriate management strategies. To explore these relationships, we amplified microsatellite and mitochondrial markers from modern caribou from across the Southern Yukon, Canada, as well as mitochondrial DNA from Holocene specimens recovered from alpine ice patches in the same region. Our analyses identify a genetically distinct group of caribou composed of herds from the Southern Lakes region that may warrant special management consideration. We also identify a partial genetic replacement event occurring 1000 years before present, coincident with the deposition of the White River tephra and the Medieval Warm Period. These results suggest that, in the face of increasing anthropogenic pressures and climate variability, maintaining the ability of caribou herds to expand in numbers and range may be more important than protecting the survival of any individual, isolated sedentary forest‐dwelling herd.     

Rapid carbon turnover beneath shrub and tree vegetation is associated with low soil carbon stocks at a subarctic treeline

Climate warming at high northern latitudes has caused substantial increases in plant productivity of tundra vegetation and an expansion of the range of deciduous shrub species. However significant the increase in carbon (C) contained within above‐ground shrub biomass, it is modest in comparison with the amount of C stored in the soil in tundra ecosystems. Here, we use a ‘space‐for‐time’ approach to test the hypothesis that a shift from lower‐productivity tundra heath to higher‐productivity deciduous shrub vegetation in the sub‐Arctic may lead to a loss of soil C that out‐weighs the increase in above‐ground shrub biomass. We further hypothesize that a shift from ericoid to ectomycorrhizal systems coincident with this vegetation change provides a mechanism for the loss of soil C. We sampled soil C stocks, soil surface CO₂ flux rates and fungal growth rates along replicated natural transitions from birch forest (Betula pubescens), through deciduous shrub tundra (Betula nana) to tundra heaths (Empetrum nigrum) near Abisko, Swedish Lapland. We demonstrate that organic horizon soil organic C (SOC_org) is significantly lower at shrub (2.98 ± 0.48 kg m^?2) and forest (2.04 ± 0.25 kg m^?2) plots than at heath plots (7.03 ± 0.79 kg m^?2). Shrub vegetation had the highest respiration rates, suggesting that despite higher rates of C assimilation, C turnover was also very high and less C is sequestered in the ecosystem. Growth rates of fungal hyphae increased across the transition from heath to shrub, suggesting that the action of ectomycorrhizal symbionts in the scavenging of organically bound nutrients is an important pathway by which soil C is made available to microbial degradation. The expansion of deciduous shrubs onto potentially vulnerable arctic soils with large stores of C could therefore represent a significant positive feedback to the climate system.     

Body Size Variations in Caribou Ecotypes and Relationships With Demography

ABSTRACT In many vertebrates size is one of the most influential and variable individual characteristics and a strong determinant of reproductive success. Body size is generally density dependent and decreases when intraspecific competition increases. Frequent and long-distance movements increase energy expenditures and, therefore, may also influence body size, particularly in highly mobile species. Caribou (Rangifer tarandus, also known as reindeer) exhibit tremendous variation in size and movements and thus represent an excellent candidate species to test the relationships between body size, population size, and movements. We analyzed body measurements of adult female caribou from 7 herds of the Québec-Labrador Peninsula, Canada, and we related their morphology to population size, movements, and annual ranges. The herds represented 3 ecotypes (migratory, montane, and sedentary). Ecotypes and herds differed in size (length), shape (roundness), and movements. The sedentary ecotype was larger and moved 4 to 7 times less than the migratory ecotype in the 1990s. At the start of a demographic growth period in the early 1960s, migratory caribou from the Rivière-George (hereafter George) herd had longer mandibles than caribou of the sedentary ecotype. Mandible length in the George herd declined in the 1980s after rapid population growth, while individuals performed extensive movements and the herd's annual range increased. Migratory caribou then became shorter than sedentary caribou. After the George herd decline in the 1990s, mandible length increased again near levels of the 1980s. Caribou from the migratory Rivière-aux-Feuilles herd later showed a similar decline in mandible length during a period of population growth, associated with longer movements and increasing annual range. We hypothesize that the density-dependent effect observed on body size might have been exerted through summer habitat degradation and movement variations during herd growth. Our study has 2 important implications for caribou management: the distinctiveness of different populations and ecotypes, and the correlations between population trajectories and changes in body condition and habitat.     

Dynamic selection for forage quality and quantity in response to phenology and insects in an Arctic ungulate

Spatiotemporal variation in forage is a primary driver of ungulate behavior, yet little is known about the nutritional components they select, and how selection varies across the growing season with changes in forage quality and quantity. We addressed these uncertainties in barren‐ground caribou (Rangifer tarandus), which experience their most important foraging opportunities during the short Arctic summer. Recent declines in Arctic caribou populations have raised concerns about the influence of climate change on summer foraging opportunities, given shifting vegetation conditions and insect harassment, and their potential effects on caribou body condition and demography. We examined Arctic caribou selection of summer forage by pairing locations from females in the Central Arctic Herd of Alaska with spatiotemporal predictions of biomass, digestible nitrogen (DN), and digestible energy (DE). We then assessed selection for these nutritional components across the growing season at landscape and patch scales, and determined whether foraging opportunities were constrained by insect harassment. During early summer, at the landscape scale, caribou selected for intermediate biomass and high DN and DE, following expectations of the forage maturation hypothesis. At the patch scale, however, caribou selected for high values of all forage components, particularly DN, suggesting that protein may be limiting. During late summer, after DN declined below the threshold for protein gain, caribou exhibited a switch at both spatial scales, selecting for higher biomass, likely enabling mass and fat deposition. Mosquito activity strongly altered caribou selection of forage and increased their movement rates, while oestrid fly activity had little influence. Our results demonstrate that early and late summer periods afford Arctic caribou distinct foraging opportunities, as they prioritize quality earlier in the summer and quantity later. Climate change may further constrain caribou access to DN as earlier, warmer Arctic summers may be associated with reduced DN and increased mosquito harassment.     

Plant production and nitrogen accumulation above- and belowground in low and tall birch tundra communities: the influence of snow and litter

Background and Aim

A vegetation transition to taller and denser deciduous shrub tundra is currently occurring in many locations across the low Arctic, and is associated with climate change. Here, we investigated if deeper snow is a mechanism for enhanced shrub growth.

Methods

To determine if a moderate and climatically realistic increase in snow depth can enhance shrub productivity, we compared growth responses between ambient and experimentally deepened snow plots in low birch hummock tundra. To determine the potential influence of factors other than deepened snow that are associated with taller, denser shrubs, we also compared shrub growth between low birch hummock and tall birch-dominated tundra.

Results

Neither deciduous shrub above- nor belowground production nor nitrogen accumulation was enhanced by deepened snow. However, deciduous birch shrub new shoot production was 23× larger and total vascular shoot to belowground biomass ratios were higher in the tall birch tundra than the birch hummock (~0.7 and ~0.4, respectively), indicating that the combination of deeper snow together with other internal feedbacks greatly enhanced birch growth.

Conclusions

Together, our results strongly suggest that the much larger litter production in tall birch ecosystems is an important internal feedback that may or may not interact with deeper snow to promote birch growth in tall shrub tundra.

     

Relationships between graminoid growth form and levels of grazing by caribou (Rangifer tarandus) in Alaska

Herbivores and their forage interact in many ways, in some instances to the benefit or detriment of herbivore and vegetation. Studies of wildebeest (Connochaetes taurinus) in Africa and snow geese (Chen caerulescens) in the Arctic have suggested that these grazers enhance graminoid production in certain sites by repeatedly using them. Other studies have concluded that herbivores are sensitive to local variation in forage quality and quantity, and preferentially use those sites that are intrinsically more productive. In this study, caribou (Rangifer tarandus) were observed foraging at different densities on two adjacent Alaskan ranges, within which particular feeding sites contained predictably high, medium, or low densities of caribou. Vegetation from one high- and one low-use site on each of the high- and low-density ranges was sampled and monitored for productivity, measured as re-growth following clipping, with the objectives of determining which forage characteristics influence usage by grazers and whether the productivity and nature of graminoid growth after clipping were related to grazing history. Forage biomass density (g/m³), shoot density (number/m²), stand densities of nutrients and minerals (g/m³), and forage concentrations of nutrients and minerals (g/100 g tissue) correlated positively with use of sites by caribou. Productivity was independent of previous use by grazers, but consistent within ranges. These results indicate that caribou are sensitive to local variation in forage quality and quantity, preferentially use those sites with higher returns of nutrients and minerals, and have the potential to enhance graminoid growth on sites that are inherently more productive.     

Wildlife species benefitting from a greener Arctic are most sensitive to shrub cover at leading range edges

Widespread expansion of shrubs is occurring across the Arctic. Shrub expansion will substantially alter arctic wildlife habitats. Identifying which wildlife species are most affected by shrubification is central to predicting future arctic community composition. Through meta‐analysis, we synthesized the published evidence for effects of canopy‐forming shrubs on birds and mammals in the Arctic and Subarctic. We examined variation in species behaviour, distribution and population dynamics in birds and mammals in response to shrub cover (including shrub cover indicators such as shrub occurrence, extent, density and height). We also assessed the degree of heterogeneity in wildlife responses to shrub cover and synthesized the remaining literature that did not fit the criteria for our quantitative meta‐analyses. Species from higher green vegetation biomass habitats (high Normalized Difference Vegetation Index, NDVI, across their distribution) were more likely to respond positively to shrub cover, demonstrating the potential for species to expand from boreal to arctic habitats under shrubification. Wildlife populations located in the lowest vegetation biomass (low NDVI) areas of their species’ range had the greatest proportion of positive responses to shrub cover, highlighting how increases in performance at leading edges of invaders distributions may be particularly rapid. This demonstrates the need to study species at these leading edges to accurately predict expansion potential. Arctic specialists were poorly represented across studies (limited to 5 bird and 0 mammal species), this knowledge gap potentially explains the few reported negative effects of shrub cover (3 of 29 species). Species responses to shrub cover showed substantial heterogeneity and varied among sites and years in all studies with sufficient replication to detect such variation. Our study highlights the importance of responses at species range edges in determining outcomes of shrubification for arctic birds and mammals and the need for greater examination of potential wildlife losers under shrubification.