Åshild Ø. Pedersen

Climate events synchronize the dynamics of a resident vertebrate community in the high Arctic.

All Together Now Environmental drivers, such as extreme weather events, impact population dynamics and can synchronize such dynamics across populations within a species. Given that many species depend on similar resources, such events might also be expected to synchronize dynamics across species, but the complexity of multispecies communities makes it difficult to reveal potential drivers in common. Hansen et al. (p. 313) took advantage of the simplicity of the year-round community on the high-arctic island of Spitsbergen to test for the presence of synchrony. Population fluctuations were synchronized across the three herbivore species (Svalbard reindeer, Svalbard rock ptarmigan, and sibling vole) and the single resident predator, the arctic fox, was in lagged synchrony. The driver of these fluctuations appears to be extreme winter rain-on-snow events that reduce the availability of winter forage due to ice cover. Reindeer, ptarmigan, vole, and fox populations on Svalbard respond together to extreme weather. Recently accumulated evidence has documented a climate impact on the demography and dynamics of single species, yet the impact at the community level is poorly understood. Here, we show that in Svalbard in the high Arctic, extreme weather events synchronize population fluctuations across an entire community of resident vertebrate herbivores and cause lagged correlations with the secondary consumer, the arctic fox. This synchronization is mainly driven by heavy rain on snow that encapsulates the vegetation in ice and blocks winter forage availability for herbivores. Thus, indirect and bottom-up climate forcing drives the population dynamics across all overwintering vertebrates. Icing is predicted to become more frequent in the circumpolar Arctic and may therefore strongly affect terrestrial ecosystem characteristics.

Warmer and wetter winters: characteristics and implications of an extreme weather event in the High Arctic

One predicted consequence of global warming is an increased frequency of extreme weather events, such as heat waves, droughts, or heavy rainfalls. In parts of the Arctic, extreme warm spells and heavy rain-on-snow (ROS) events in winter are already more frequent. How these weather events impact snow-pack and permafrost characteristics is rarely documented empirically, and the implications for wildlife and society are hence far from understood. Here we characterize and document the effects of an extreme warm spell and ROS event that occurred in High Arctic Svalbard in January–February 2012, during the polar night. In this normally cold semi-desert environment, we recorded above-zero temperatures (up to 7 °C) across the entire archipelago and record-breaking precipitation, with up to 98 mm rainfall in one day (return period of >500 years prior to this event) and 272 mm over the two-week long warm spell. These precipitation amounts are equivalent to 25 and 70% respectively of the mean annual total precipitation. The extreme event caused significant increase in permafrost temperatures down to at least 5 m depth, induced slush avalanches with resultant damage to infrastructure, and left a significant ground-ice cover (∼5–20 cm thick basal ice). The ground-ice not only affected inhabitants by closing roads and airports as well as reducing mobility and thereby tourism income, but it also led to high starvation-induced mortality in all monitored populations of the wild reindeer by blocking access to the winter food source. Based on empirical-statistical downscaling of global climate models run under the moderate RCP4.5 emission scenario, we predict strong future warming with average mid-winter temperatures even approaching 0 °C, suggesting increased frequency of ROS. This will have far-reaching implications for Arctic ecosystems and societies through the changes in snow-pack and permafrost properties.

Prevalence of nest predators in a sub-Arctic ecosystem

High nest loss is an important driver of gallinaceous bird population dynamics. Identifying factors determining the spatial distribution of potential nest predators and thereby indirectly risk of nest losses is therefore essential. The aim of this 1-year study was to estimate relative predation rates on artificial ground nests in willow ptarmigan (Lagopus lagopus) habitats, along replicate altitudinal gradients (transects, n = 60) spanning from sub-Arctic birch forest to the low-alpine tundra in three locations in northern Norway. In each transect, one artificial nest (track board) was placed in three different habitats: (1) birch forest, (2) edge between birch forest and low-alpine tundra and (3) low-alpine tundra. Total predation rates over all habitats within locations ranged from 47.4% to 77.5% and did not vary systematically in space and time. The average predation rate by avian predators was consistently high (58%), and mammalian predation rate was consistently low (5.6%). The consistently high level of predation inflicted by birds was mainly due to omnipresent corvids, especially the hooded crow (Corvus cornix). Analysis of species-specific predation rates showed that habitat and location effects were insignificant for all species, except for raven (Corvus corax) that showed clearly higher predation in one of the locations. The results indicate that from the perspective of the spatial distribution of potential nest predators in sub-Arctic birch forest, ground nesting birds like willow ptarmigan should not be expected to be selective with respect to nesting habitat in the ecotone between birch forest and the low-alpine tundra.

Rock Ptarmigan (Lagopus muta) breeding habitat use in northern Sweden

AbstractAlpine and arctic tundra regions are likely to retract as a result of climate warming and concerns have been raised over the status of the Rock Ptarmigan (Lagopus muta). In Fennoscandia, the Rock Ptarmigan has low population abundance, and predictions based on harvest statistics show population declines throughout the range. In this study, we used a long-term opportunistic dataset of Rock Ptarmigan observations, environmental predictors derived from a digital vegetation map and a digital elevation model to describe the breeding distribution at three different ecological scales. Patterns of spatial distribution were similar across all the three study scales. The presence of permanent snow-fields positively influenced the occurrence of Rock Ptarmigan at the territory and landscape scale. Open vegetation, rock-dominated areas and, in particular, dry heath influenced Rock Ptarmigan presence positively at all scales. Altitude and terrain heterogeneity were important variables at all scales, with higher probabilities of Rock Ptarmigan being present at intermediate altitude ranges, with a high degree of terrain heterogeneity. This is the first study to describe Rock Ptarmigan breeding distribution in Fennoscandia and our findings yield new insights into the environmental variables that are important for the spatial distribution of Rock Ptarmigan during the breeding season. When planning conservation efforts, this information should be used to inform management regarding the protection of core areas and buffer zones related to the conservation and harvest management of the Rock Ptarmigan.ZusammenfassungBruthabitatnutzung beim Alpenschneehuhn (Lagopus muta) in Nordschweden Es ist zu erwarten, dass alpine und arktische Tundralebensräume in Folge der Klimaerwärmung schrumpfen, und es wurden bereits Bedenken bezüglich des Status des Alpenschneehuhns (Lagopus muta) laut. In Fennoskandinavien kommt das Alpenschneehuhn in geringer Populationsdichte vor, und Prognosen auf der Grundlage von Jagdstatistiken zeigen Bestandsrückgänge im gesamten Verbreitungsgebiet. Für diese Studie verwendeten wir einen über einen längeren Zeitraum gesammelten Datensatz mit Zufallsbeobachtungen von Alpenschneehühnern, dazu unabhängige Umweltvariablen aus einer digitalen Vegetationskarte und ein digitales Höhenmodell, um die Brutverbreitung auf drei verschiedenen ökologischen Ebenen zu beschreiben. Die räumlichen Verbreitungsmuster waren für alle drei in der Studie betrachteten Ebenen ähnlich. Das Vorhandensein dauerhafter Schneefelder hatte einen positiven Einfluss auf das Vorkommen von Alpenschneehühnern, sowohl auf Revier- als auch auf Landschaftsebene. Offene Vegetation, felsenreiche Flächen und speziell trockenes Heideland beeinflussten das Vorkommen von Alpenschneehühnern auf allen drei Ebenen positiv. Die Variablen „Höhenstufe“ und „Heterogenität des Geländes“ waren auf jeder Ebene wichtig; die Wahrscheinlichkeit eines Alpenschneehuhn-Vorkommens war in mittleren Höhenlagen mit starker Geländeheterogenität höher. Dies ist die erste Untersuchung, die sich mit der Brutverbreitung des Alpenschneehuhns in Fennoskandinavien befasst, und unsere Befunde liefern neue Erkenntnisse darüber, welche Umweltvariablen für die räumliche Verteilung der Alpenschneehühner während der Brutzeit von Bedeutung sind. Bei der Planung von Naturschutzmaßnahmen sollten den für das Schutz- und Jagdmanagement Verantwortlichen die für die Gewährleistung von Kernund Pufferzonen relevanten Informationen zur Verfügung gestellt werden.

Scale-Dependent Responses of Predators and Their Prey to Spruce Plantations in Subarctic Birch Forests in Winter

Abstract: Planting of non-native spruce in subarctic birch forests introduces new habitats that change the landscape mosaic and increase the extent of artificial edges. This may alter the spatio-temporal predator—prey dynamics. In this study, we focused on small- to medium-sized ground-dwelling prey species and their mammalian predators in winter. In a spatially extensive snow-tracking study over 3 winters (2003–2005), we explored the spatial distribution of species at 3 spatial scales ranging from forest stands to landscape mosaics. We documented scale- and time-dependent responses to spruce plantations for red fox, stoat, mountain hare, and voles, which were the dominant species in the study. However, the responses to spruce plantations were mostly inconsistent across scales. A small-scale affinity for plantation edges, largely consistent over time, was found for all species. By contrast, habitat selection for and against spruce plantations at stand scale alternated profoundly among the different years, although in qualitatively similar patterns among the dominant species, which suggests a common cause. At the landscape scale only red fox was negatively related to proportion of spruce plantations, while mountain hares exhibited annual shifts in occurrence relative to the amount of spruce. Predators and prey were spatially and temporally related at the 2 smallest scales (i.e., within and among forest stands) in a manner that may be explained by year- and standspecific snow conditions affecting the predator—prey interactions within the community.

Spatial patterns of goose grubbing suggest elevated grubbing in dry habitats linked to early snowmelt

The western Palaearctic tundra is a breeding habitat for large populations of European geese. After their arrival in spring, pink-footed geese (Anser brachyrhynchus) forage extensively on below-ground plant parts, using a feeding technique called grubbing that has substantial impact on the tundra vegetation. Previous studies have shown a high frequency of grubbing in lowland fen vegetation. In the present study, we examined the occurrence of grubbing in other habitat types on Spitsbergen, in the Arctic archipelago of Svalbard. Goose grubbing was surveyed along 19 altitudinal transects, going from the valley bottom to altitudes dominated by scree. Grubbing was more frequent in the wet habitat type at low altitudes compared to the drier habitat type at higher altitudes. For the dry habitat type, a higher frequency of grubbing was found in study plots with a south-east facing exposure where snowmelt is expected to be early. This suggests that pink-footed geese primarily use dry vegetation types for grubbing when they are snow-free in early spring and the availability of snow-free patches of the preferred wet vegetation types in the lowlands is limited. Dry vegetation types have poorer recovery rates from disturbance than wet ones. Sites with early snowmelt and dry vegetation types may therefore be at greater risk of long-term habitat degradation. We conclude that the high growth rate of the Svalbard-breeding pink-footed goose population suggests that increasing impacts of grubbing can be expected and argue that a responsible monitoring of the effects on the tundra ecosystem is crucial.

Complementary use of density estimates and hunting statistics: different sides of the same story?

The use of hunting statistics for population monitoring has often been criticized because such data are affected by several sources of error. Still, for many harvested populations, hunting statistics are the only available data source and cautious use of such data may be valuable for management. Here we assessed to what extent long-term monitoring of Svalbard rock ptarmigan spring densities and hunting statistics (bag size and proportion of juveniles in the hunting bag) reflect similar population fluctuations. We found a decreasing trend in both bag size and proportion of juveniles in the bag, but no trend in ptarmigan spring densities. However, annual fluctuations of ptarmigan spring density and bag size were correlated. Together, these time series indicate that both population abundance (bag size) and recruitment (proportion of juveniles in the bag) are decreasing, but the reproductive component fraction (density of territorial males) is not yet compromised. This biological interpretation remains, however, uncertain due to lack of hunting effort data. Monitoring programs using hunting statistics should therefore critically discuss and evaluate what the hunting statistics reflect and fine-tune the hunter data collection to obtain maximum biological relevance. Still, our results illustrate that the combination of population estimates and hunting statistics can provide more nuanced information about the population status than the density estimates alone.

Changed Arctic-alpine food web interactions under rapid climate warming: implication for ptarmigan research

Ptarmigan are herbivorous birds that are year-round residents of alpine and arctic ecosystems — presently subjected to the most rapid climate warming on earth. Yet, compared to other bird taxa there has been little climate impact research on ptarmigan. Ptarmigan population dynamics, in particular in the sub/low-arctic, appears to be strongly influenced by complex interactions with a suite of functionally diverse predators in the food webs. We review evidence supporting that the strength of such predator—ptarmigan interactions has been altered, most likely due to climate change, having led to rapidly declining ptarmigan populations and in some places national red listing. Predation-mediated population declines are likely linked to dampened population cycles of keystone mammal herbivores (inducing increased apparent competition/reduced apparent mutualism), altitudinal/latitudinal expansions of boreal mesopredators and possibly mismatched ptarmigan plumage colour in spring and fall. Yet, other rapid food web mediated impacts are likely to act bottom—up, such as phenological mismatches with food plants and competitive interactions with other irrupting herbivores. We advocate that ptarmigan researchers should team up with specialists on other taxa in order to adopt a food web approach to their research. Coordinated action of research teams, to make comparative studies among ptarmigan species or populations imbedded in food webs of varying structure or ambient climate, may be rewarding in the age of rapid ongoing climate changes.

Nest-predator prevalence along a mountain birch–alpine tundra ecotone

Dette er postprint versjonen av en artikkel publisert i Wildlife Research. Den publiserte versjonen av artikkelen kan finnes her: http://www.publish.csiro.au/paper/WR11031

Snowmobile impact on diurnal behaviour in the Arctic fox

ABSTRACT As tourism increases globally, studies have documented impacts on wildlife from anthropogenic disturbances. In this observational experiment we aimed to investigate if snowmobile traffic affected the diurnal activity of Arctic fox in High Arctic Svalbard. We conducted the study in two areas in Svalbard, one control area with low snowmobile traffic and one experimental area with high snowmobile traffic. In each area 10 camera-traps, baited with reindeer carcasses, were positioned and programmed to take photographs every five minutes. The proportion of photographs with foxes was higher during the night than during the day, and the difference between night and day was larger in the area with more snowmobile traffic. By using data obtained according to a similar study design in two Arctic Russian sites, Yamal and Nenetsky, with little human activity and low snowmobile traffic, we were able to compare Arctic fox activity patterns in Svalbard on a larger scale. Our results indicate that snowmobile traffic had an impact on the diurnal activity of the Arctic fox in Svalbard, while there were no obvious diurnal activity patterns among Russian foxes. Even the area with low snowmobile traffic in Svalbard showed increased use of the reindeer carcasses during the night compared to one of the Russian sites, where foxes used carcasses equally during day and night. Such knowledge is of importance in designing cautious management practices.