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Understanding and predicting large-scale ecological responses to global environmental change requires comparative studies across geographic scales with coordinated efforts and standardized methodologies. We designed, applied and assessed standardized protocols to measure tundra herbivory at three spatial scales: plot, site (habitat), and study area (landscape). The plot and site-level protocols were tested in the field during summers 2014-2015 at eleven sites, nine of them comprising warming experimental plots included in the International Tundra Experiment (ITEX). The study area protocols were assessed during 2014-2018 at 24 study areas across the Arctic. Our protocols provide comparable and easy-to-implement methods for assessing the intensity of invertebrate herbivory within ITEX plots and for characterizing vertebrate herbivore communities at larger spatial scales. We discuss methodological constraints and make recommendations for how these protocols can be used and how sampling effort can be optimized to obtain comparable estimates of herbivory, both at ITEX sites and at large landscape scales. The application of these protocols across the tundra biome will allow characterizing and comparing herbivore communities across tundra sites and at ecologically relevant spatial scales, providing an important step towards a better understanding of tundra ecosystem responses to large-scale environmental change. CGB was funded by the Estonian Research Council (grant IUT 20-28), and the European Regional Development Fund (Centre of Excellence EcolChange). JDMS was supported by the Research Council of Norway (262064). OG and LB were supported by the French Polar Institute (program “1036 Interactions”) and PRC CNRS Russie 396 (program “ICCVAT”). DSH, NL, MAG, JB and JDR were supported by the Natural Sciences and Engineering Research Council (Canada). NL, MAG, JB and JDR were supported by the Polar Continental Shelf Program. NL was supported by the Canada Research Chair program and the Canada Foundation for Innovation. NL and JB were supported by Environment Canada and Polar Knowledge Canada. NL and MAG were supported by the Government of Nunavut, the Igloolik Community, and Université de Moncton. NL, MAG and JB were supported by the Northern Scientific Training Program. JMA was funded by Carl Tryggers stiftelse för vetenskaplig forskning and Qatar Petroleum (QUEX-CAS-QP-RD-18_19). IHM-S was funded by the UK Natural Environmental Research Council Shrub Tundra (NE/M016323/1) grant. ISJ was funded by the University of Iceland Research Fund. Fieldwork in Yamal peninsula (Erkuta, Sabetta and Belyi) for DE, NS and AS was supported by the Russian Foundation for Basic Research (No: 18-05-60261 and No: 18-54-15013), Fram Centre project YaES (No: 362259), the Russian Center of Development of the Arctic, and the “Yamal-LNG” company. Fieldwork in Utqiaġvik was supported by the U.S. Fish and Wildlife Service. Fieldwork in Svalbard was supported by the Norwegian Research Council (AFG No: 246080/E10), the Norwegian Polar Institute, Climate-ecological Observatory for Arctic Tundra – COAT, the Svalbard Environmental protection fund (project number 15/20), and the University Centre in Svalbard (UNIS) and the AB-338/AB-838 students of 2018. Sampling at Billefjorden was supported by GACR 17- 20839S.

Rain-on-Snow (ROS) events change snow pack properties and in extreme cases ice layers form which affect wildlife, vegetation and soils beyond the duration of the event. Active as well as passive microwave sensors have been used in the past to document ROS on regional scale. Either wet snow during a ROS event or the formation of crust afterwards are identified in most cases. The fusion of both approaches is promising for circumpolar monitoring.C-band radar is of special interest due to good data availability including a range of nominal spatial resolution (10 m–12.5 km). Previous studies indicated that radar backscatter is suitable to identify snow structure change. As an example L-band passive microwave observations from SMOS and C-band backscatter from Metop ASCAT have been jointly analysed and compared to snowpit observations in Scandinavia and Northwestern Siberia.A circumpolar dataset of potential ROS has been created. The gridded information has been eventually aggregated for events. Larger mid-winter events have been eventually extracted for 2012-2021. They occur mostly in the NE part of northern Eurasia (mostly November) and across Alaska (mostly December). The spatiotemporal patters of these events and the magnitude of snow structure change will be presented and discussed.

Camera trap arrays can generate thousands to millions of images that require exorbitant time and effort to classify and annotate by trained observers. Computer vision has evolved as an automated alternative to manual classification. The most popular computer vision solution is the supervised Machine Learning technique, which uses labeled images to train automated classification algorithms.We propose a multi-step semi-automated workflow that consists of (1) identifying and separating bad-from good-quality images, (2) parsing good images into animals, humans, vehicles, and empty, and (3) cropping animals from images and classifying them into species for manual inspection. We trained, validated, and evaluated this approach using 548,627 images from 46 cameras in two regions of the Arctic (northeastern Norway, and Yamal Peninsula, Russia).We obtained an accuracy of 0.959 for all three steps combined with the complete year test data set at Varanger and 0.922 at Yamal, reducing the number of images that required manual inspection to 7.9% of the original set from Varanger and 3.2% from Yamal.Researchers can modify this multi-step process to meet their specific needs for monitoring and surveying wildlife, providing greater flexibility than current options available for image classification.

Accelerating climate change is causing severe habitat fragmentation in the Arctic, threatening the persistence of many cold-adapted species. The Scandinavian arctic fox (Vulpes lagopus) is highly fragmented, with a once continuous, circumpolar distribution, it struggled to recover from a demographic bottleneck in the late 19th century. The future persistence of the entire Scandinavian population is highly dependent on the northernmost Fennoscandian subpopulations (Scandinavia and the Kola Peninsula), to provide a link to the viable Siberian population. By analyzing 43 arctic fox genomes, we quantified genomic variation and inbreeding in these populations. Signatures of genome erosion increased from Siberia to northern Sweden indicating a stepping-stone model of connectivity. In northern Fennoscandia, runs of homozygosity (ROH) were on average ~1.47-fold longer than ROH found in Siberia, stretching almost entire scaffolds. Moreover, consistent with recent inbreeding, northern Fennoscandia harbored more homozygous deleterious mutations, whereas Siberia had more in heterozygous state. This study underlines the value of documenting genome erosion following population fragmentation to identify areas requiring conservation priority. With the increasing fragmentation and isolation of Arctic habitats due to global warming, understanding the genomic and demographic consequences is vital for maintaining evolutionary potential and preventing local extinctions.

Rain-on-snow (ROS) events occur across many regions of the terrestrial Arctic in mid-winter. Snowpack properties are changing, and in extreme cases ice layers form which affect wildlife, vegetation and soils beyond the duration of the event. Specifically, satellite microwave observations have been shown to provide insight into known events. Only Ku-band radar (scatterometer) has been applied so far across the entire Arctic. Data availability at this frequency is limited, however. The utility of other frequencies from passive and active systems needs to be explored to develop a concept for long-term monitoring. The latter are of specific interest as they can be potentially provided at higher spatial resolution. Radar records have been shown to capture the associated snow structure change based on time-series analyses. This approach is also applicable when data gaps exist and has capabilities to evaluate the impact severity of events. Active as well as passive microwave sensors can also detect wet snow at the timing of an ROS event if an acquisition is available. The wet snow retrieval methodology is, however, rather mature compared to the identification of snow structure change since ambiguous scattering behaviour needs consideration. C-band radar is of special interest due to good data availability including a range of nominal spatial resolutions (10 m–12.5 km). Scatterometer and SAR (synthetic aperture radar) data have therefore been investigated. The temperature dependence of C-band backscatter at VV (V – vertical) polarization observable down to −40 ∘C is identified as a major issue for ROS retrieval but can be addressed by a combination with a passive microwave wet snow indicator (demonstrated for Metop ASCAT – Advanced Scatterometer – and SMOS – Soil Moisture and Ocean Salinity). Results were compared to in situ observations (snowpit records, caribou migration data) and Ku-band products. Ice crusts were found in the snowpack after detected events (overall accuracy 82 %). The more crusts (events) there are, the higher the winter season backscatter increase at C-band will be. ROS events captured on the Yamal and Seward peninsulas have had severe impacts on reindeer and caribou, respectively, due to ice crust formation. SAR specifically from Sentinel-1 is promising regarding ice layer identification at better spatial details for all available polarizations. The fusion of multiple types of microwave satellite observations is suggested for the creation of a climate data record, but the consideration of performance differences due to spatial and temporal cover, as well as microwave frequency, is crucial. Retrieval is most robust in the tundra biome, where results are comparable between sensors. Records can be used to identify extremes and to apply the results for impact studies at regional scale.

Accelerating climate change is causing severe habitat fragmentation in the Arctic, threatening the persistence of many cold-adapted species. The Scandinavian arctic fox (

The Arctic fox (Vulpes lagopus L.) population on the Kola Peninsula occupies an intermediate, and potentially connecting, position between foxes living on the Scandinavian Peninsula and populations further east in Russia, but very little is known about the status of this population. Here we summarize data from the literature, forgotten archival sources about research in the first half of the twentieth century, and the results of several independent expeditions undertaken over the past two decades. These materials include data on fur harvesting, incomplete monitoring data from official winter track counts of game animals, local knowledge, and our own observations. Our research revealed the extremely poor state of the Arctic fox population on the Kola Peninsula. According to our estimates, the current population is likely isolated and consists of no more than a few dozen adults. The fur return data, together with long-term data on small rodent abundance, suggest that irregular and fading out lemming cycles were a major driver of the Arctic fox population decline. The thorough research from the 1930s contrasts strongly with the lack of interest in studying and monitoring the population in recent decades, which is not even listed as a threatened species in the regional Red Data Book. In fact, the work performed here filled a more than a half-century gap in the study of the population and allowed us to determine the urgent need to resume research and immediately take active measures to protect and promote the recovery of the species in the region.

Studies of the effects of variation in resource availability are important for understanding the ecology of high-latitude mammals. This paper examines the potential of dental evidence (tooth wear and breakage) as a proxy for diet and food choice in Vulpes lagopus, the Arctic fox. It presents a preliminary study of dental microwear, gross wear score, and tooth breakage in a sample (n = 78 individuals) from the Yamal Peninsula of the Russian Arctic. While these measures have each been associated with feeding ecology in larger carnivorans (e.g., proportion of bone in the diet), they have yet to be combined in any study and have rarely been applied to smaller species or those from high latitudes. Arctic foxes from the north and south of the peninsula, and those from rodent peak and trough density periods, are compared to assess impact of changes in food availability across space and time. Results indicate that microwear textures vary in dispersion, with more variation in texture complexity, including higher values (suggesting more consumption of bone), in the rodent-poor period in the north of Yamal. Gross wear scores and tooth breakage are also significantly higher for the north of Yamal than the south. These data together suggest that dental evidence can provide important insights into variation in the feeding ecology of Arctic foxes and potentially into the impacts of changes in food abundance across space and time.

Publisher's version (útgefin grein), Climatic impacts are especially pronounced in the Arctic, which as a region is warming twice as fast as the rest of the globe. Here, we investigate how mean climatic conditions and rates of climatic change impact parasitoid insect communities in 16 localities across the Arctic. We focus on parasitoids in a widespread habitat, Dryas heathlands, and describe parasitoid community composition in terms of larval host use (i.e., parasitoid use of herbivorous Lepidoptera vs. pollinating Diptera) and functional groups differing in their closeness of host associations (koinobionts vs. idiobionts). Of the latter, we expect idiobionts—as being less fine‐tuned to host development—to be generally less tolerant to cold temperatures, since they are confined to attacking hosts pupating and overwintering in relatively exposed locations. To further test our findings, we assess whether similar climatic variables are associated with host abundances in a 22 year time series from Northeast Greenland. We find sites which have experienced a temperature rise in summer while retaining cold winters to be dominated by parasitoids of Lepidoptera, with the reverse being true for the parasitoids of Diptera. The rate of summer temperature rise is further associated with higher levels of herbivory, suggesting higher availability of lepidopteran hosts and changes in ecosystem functioning. We also detect a matching signal over time, as higher summer temperatures, coupled with cold early winter soils, are related to high herbivory by lepidopteran larvae, and to declines in the abundance of dipteran pollinators. Collectively, our results suggest that in parts of the warming Arctic, Dryas is being simultaneously exposed to increased herbivory and reduced pollination. Our findings point to potential drastic and rapid consequences of climate change on multitrophic‐level community structure and on ecosystem functioning and highlight the value of collaborative, systematic sampling effort., We are grateful for data from the Greenland Ecosystem Monitoring Programme provided by the Department of Bioscience, Aarhus University, Denmark, in collaboration with Greenland Institute of Natural Resources, Nuuk, Greenland, and the Department of Biology, University of Copenhagen, Denmark, and data from the Greenland Ecosystem Monitoring Programme provided by Asiaq—Greenland Survey, Nuuk, Greenland. We acknowledge CSC–IT Center for Science Ltd., Espoo, Finland, for the allocation of computational resources. Rósa Erlendsdóttir kindly provided access to the sampling site in Votilækur, Iceland. We thank Marie‐Andree Giroux and Kristen Peck for their assistance in Igloolik and Marjo Kilpinen, Eija Takala and Emma Hakanen for their hard work in the laboratory. We gratefully acknowledge funding from the Academy of Finland (grants 276909, 285803 to T.R., and 276671 to M.V.K.), Nessling Foundation (grants 201700420, 201600034, 201500090 to T.K.), Jane and Aatos Erkko Foundation, Societas pro Fauna et Flora Fennica, The Danish Environmental Protection Agency (N.M.S.), French Polar Institute‐IPEV (program “Interactions 1036” to O.G. and B.S.), INTERACT, Russian Foundation for Basic Research (grant 18‐05‐60261 to A.S. and N.S.), Research Council of Norway (grant 249902/F20), the Natural Sciences and Engineering Research Council of Canada (PGS‐D award to S.K.M., CGS‐D award to A.M.S., Discovery Grant to J.B.), Churchill Northern Studies Centre (Northern Research Fund Award to A.M.S. and M.P.), Canadian Polar Commission (Northern Scientific Training Program Award to D.L.B., K.H.I.D., S.K.M., A.M.S., and M.P.), ArcticNet, Polar Continental Shelf Project, Parks Canada, Fonds Québécois de Recherche ‐ Nature et Technologies, Polar Knowledge Canada, Entomological Society of Canada, University of Guelph. The Icelandic Research Fund (Rannsóknasjóður, grant nr 152468‐051 to I.C.B.). Thanks to PhyloPic contributors Gareth Monger and Melissa Broussard.

1. Large carnivores influence ecosystem dynamics in multiple ways, for example, by suppressing meso-carnivores and providing carrions for smaller scavengers. Loss of large carnivores is suggested to cause meso-carnivore increase and expansion. Moreover, competition between meso-carnivores may be modified by the presence of larger carnivores. In tundra ecosystems, the smallest meso-carnivore, the Arctic fox, has experienced regional declines, whereas its larger and competitively superior congener, the red fox, has increased, potentially due to changes in the abundance of apex predators. 2. We explored if variation in the occurrence of wolverine and golden eagle impacted the occurrence and co-occurrence of the Arctic fox and red fox in relation to varying abundances of small rodents within the Scandinavian tundra. 3. We applied multi-species occupancy models to an extensive wildlife camera dataset from 2011–2020 covering 98 sites. Daily detection/non-detection of each species per camera trap site and study period (late winter; March–May) was stacked across years, and species occupancy was related to small rodent abundance while accounting for time of the year and status of simulated carcass. 4. The Arctic fox was more likely to co-occur with the red fox when the wolverine was present and less likely to co-occur with the red fox when golden eagles were present and the wolverine was absent. Red foxes increased in occupancy when co-occurring with the larger predators. The Arctic fox responded more strongly to small rodent abundance than the red fox and co-occurred more often with the other species at carcasses when rodent abundance was low. 5. Our findings suggest that the interspecific interactions within this tundra predator guild appear to be surprisingly intricate, driven by facets of fear of predation, interspecific mediation and facilitation, and food resource dynamics. These dynamics of intraguild interactions may dictate where and when conservation actions targeted towards the Arctic fox should be implemented.

Selecting the right location for a den during the breeding season is a type of habitat selection in the Arctic fox (Vulpes lagopus) that is likely to affect its reproductive success. A den’s suitability likely depends on its ability to provide shelter, as well as its proximity to prey resources. Depending on the different relative risks that Arctic foxes may face across their broad circumpolar range, Arctic foxes may place different emphases on selection for shelter and prey resources in different ecosystems. Understanding the different requirements for reproduction under different ecological conditions is highly relevant to conservation efforts in areas where Arctic foxes are threatened by rapid environmental changes. Here, we investigated the relative selection for shelter and prey resources in southern Yamal Peninsula (Russia) using data from 45 dens collected over a 13-year period. Arctic foxes preferred to breed in dens with more den entrances; an indicator of shelter quality. Arctic foxes also preferred dens surrounded by more prey resources (quantified by the amount of river valley habitat), but this result was less conclusive. These results complement the findings reported from other study areas, illustrating that Arctic foxes in ecosystems with diverse predator communities may put emphasis on selection for shelter quality. In less productive ecosystems, Arctic foxes may rather put emphasis on selection for prey resources. As tundra ecosystems become more productive and generalist predators move north, the reproductive requirements and habitat selection of Arctic foxes may change accordingly, depending on the species’ ability to adapt.

Most birds incubate their eggs to allow embryo development. This behaviour limits the ability of adults to perform other activities. Hence, incubating adults trade-off incubation and nest protection with foraging to meet their own needs. Parents can either cooperate to sustain this trade-off or incubate alone. The main cause of reproductive failure at this reproductive stage is predation and adults reduce this risk by keeping the nest location secret. Arctic sandpipers are interesting biological models to investigate parental care evolution as they may use several parental care strategies. The three main incubation strategies include both parents sharing incubation duties (?biparental?), one parent incubating alone (?uniparental?), or a flexible strategy with both uniparental and biparental incubation within a population (?mixed?). By monitoring the incubation behaviour in 714 nests of seven sandpiper species across 12 arctic sites, we studied the relationship between incubation strategy and nest predation. First, we described how the frequency of incubation recesses (NR), their mean duration (MDR), and the daily total duration of recesses (TDR) vary among strategies. Then, we examined how the relationship between the daily predation rate and these components of incubation behaviour varies across strategies using two complementary survival analysis. For uniparental and biparental species, the daily predation rate increased with the daily total duration of recesses and with the mean duration of recesses. In contrast, daily predation rate increased with the daily number of recesses for biparental species only. These patterns may be attributed to two independent mechanisms: cryptic incubating adults are more difficult to locate than unattended nests and adults departing the nest or feeding close to the nest can draw predators' attention. Our results demonstrate that incubation behaviour as mediated by incubation strategy has important consequences for sandpipers? reproductive success. This article is protected by copyright. All rights reserved.

This is a pre-print of an article published in Oecologia. The final authenticated version is available online at: https://doi.org/10.1007/s00442-019-04580-0 Identifying resources driving long-term trends in predators is important to understand ecosystem changes and to manage populations in the context of conservation or control. The arctic fox population in Iceland has increased steadily over a period of 30 years, an increase that has been attributed to an overall increase in food abundance. We hypothesized that increasing populations of geese or seabirds were driving this growth. We analyzed stable isotopes in a long-term series of collagen samples to determine the role of these different resources. The isotopic signatures of arctic foxes differed consistently between coastal and inland habitats. While δ15N displayed a non-linear change over time with a slight increase in the first part of the period followed by a decline in both habitats, δ13C was stable. Stable isotope mixing models suggested that marine resources and rock ptarmigan were the most important dietary sources, with marine resources dominating in coastal habitats and rock ptarmigan being more important inland. Our results suggest that seabirds may have been driving the arctic fox population increase. The rapidly increasing populations of breeding geese seem to have played a minor role in arctic fox population growth, as rock ptarmigan was the most important terrestrial resource despite a considerable decrease in their abundance during recent decades. This study shows that a long-term population trend in a generalist predator may have occurred without a pronounced change in main dietary resources, despite ongoing structural changes in the food web, where one species of herbivorous birds increased and another decreased.

Lemmings are a key component of tundra food webs and changes in their dynamics can affect the whole ecosystem. We present a comprehensive overview of lemming monitoring and research activities, and assess recent trends in lemming abundance across the circumpolar Arctic. Since 2000, lemmings have been monitored at 49 sites of which 38 are still active. The sites were not evenly distributed with notably Russia and high Arctic Canada underrepresented. Abundance was monitored at all sites, but methods and levels of precision varied greatly. Other important attributes such as health, genetic diversity and potential drivers of population change, were often not monitored. There was no evidence that lemming populations were decreasing in general, although a negative trend was detected for low arctic populations sympatric with voles. To keep the pace of arctic change, we recommend maintaining long-term programmes while harmonizing methods, improving spatial coverage and integrating an ecosystem perspective. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1007/s13280-019-01198-7) contains supplementary material, which is available to authorized users.

Indirect effects of climate change are often mediated by trophic interactions and consequences for individual species depend on how they are tied into the local food web. Here we show how the response of demographic rates of an arctic bird of prey to fluctuations in small rodent abundance changed when small rodent community composition and dynamics changed, possibly under the effect of climate warming. We observed the breeding biology of rough‐legged buzzards (Buteo lagopus) at the Erkuta Tundra Monitoring Site in southern Yamal, low arctic Russia, for 19 years (1999–2017). At the same time, data on small rodent abundance were collected and information on buzzard diet was obtained from pellet dissection. The small rodent community experienced a shift from high‐amplitude cycles to dampened fluctuations paralleled with a change in species composition toward less lemmings and more voles. Buzzards clearly preferred lemmings as prey. Breeding density of buzzards was positively related to small rodent abundance, but the shift in small rodent community lead to lower numbers relative to small rodent abundance. At the same time, after the change in small rodent community, the average number of fledglings was higher relative to small rodent abundance than earlier. These results suggest that the buzzard population adapted to a certain degree to the changes in the major resource, although at the same time density declined. The documented flexibility in the short‐term response of demographic rates to changes in structure and dynamics of key food web components make it difficult to predict how complex food webs will be transformed in a warmer Arctic. The degree of plasticity of functional responses is indeed likely to vary between species and between regions, depending also on the local food web context.

This is a post-peer-review, pre-copyedit version of an article published in Ambio. The final authenticated version is available online at: http://dx.doi.org/10.1007/s13280-019-01198-7. Lemmings are a key component of tundra food webs and changes in their dynamics can affect the whole ecosystem. We present a comprehensive overview of lemming monitoring and research activities, and assess recent trends in lemming abundance across the circumpolar Arctic. Since 2000, lemmings have been monitored at 49 sites of which 38 are still active. The sites were not evenly distributed with notably Russia and high Arctic Canada underrepresented. Abundance was monitored at all sites, but methods and levels of precision varied greatly. Other important attributes such as health, genetic diversity and potential drivers of population change, were often not monitored. There was no evidence that lemming populations were decreasing in general, although a negative trend was detected for low arctic populations sympatric with voles. To keep the pace of arctic change, we recommend maintaining long-term programmes while harmonizing methods, improving spatial coverage and integrating an ecosystem perspective.

Snøskohare – og gaupesyklusene i det boreale Nord-Amerika er et av de best kjente eksempler på populasjonssykluser. Sammenlignet med andre sykliske arter har denne syklusen en relativ konstant periode på 9–10 år. Haretettheten varierer typisk 20–30 ganger mellom topp- og bunnår. Mye økologisk forskning har ved hjelp av forskjellige metoder forsøkt å avdekke årsakene til snøskoharesyklusene, også med imponerende storskala felteksperimenter. Predasjon er den viktigste syklusdriveren, og i tillegg til direkte dødelighet, kan også stress fra intens jakt fra rovdyr og matmangel i nedgangsfasen spille en rolle. Snøskoharen er en nøkkelart i det boreale økosystemet i Nord-Amerika og et viktig byttedyr ikke bare for gaupe, men også for mange andre predatorer som coyote, rødrev eller hubro. Gjennom direkte og indirekte interaksjoner i næringsnettet påvirker snøskoharen dynamikken til store deler av økosystemet. Snøskoharen og den kanadiske gaupa er betydelig mindre enn de eurasiske hare- og gaupeartene, og bare de nordamerikanske artene har så klare og godt dokumenterte populasjonssykluser.

Human-wildlife problems often arise when predators kill livestock. This can develop into serious conflicts between traditional pastoralists and other stakeholders, such as government officials and conservationists. In the Yamal Peninsula (Russia), nearly half of the indigenous Nenets people are reindeer herders. They have recently faced many challenges, such as high mortality of reindeer from pasture icing or disease outbreaks. In addition, predation of arctic fox on reindeer calves is perceived as an increasing problem. Here, we use an interdisciplinary approach to study this emerging predation problem. We present here results from semi-structured interviews with indigenous people, as well as from biological monitoring of fox populations. Our field data were obtained in Erkuta, in the south of Yamal and in Sabetta in the north, close to a newly built industrial settlement. We show how different factors may have come together to create a problematic situation. These factors include the abandonment of the fur trade in the 1990s, the building of huge industrial facilities providing possible resource subsidies and the increasing frequency of abnormal weather events leading to weak reindeer, high reindeer mortality and abundant carcasses as resources for predators. We discuss how each of these factors affects the abundance of predators as well as the understanding of the herders.

Most birds incubate their eggs, which requires time and energy at the expense of other activities. Birds generally have two incubation strategies: biparental where both mates cooperate in incubating eggs, and uniparental where a single parent incubates. In harsh and unpredictable environments, incubation is challenging due to high energetic demands and variable resource availability. We studied the relationships between the incubation behaviour of sandpipers (genus Calidris) and two environmental variables: temperature and a proxy of primary productivity (i.e. NDVI). We investigated how these relationships vary between incubation strategies and across species among strategies. We also studied how the relationship between current temperature and incubation behaviour varies with previous day's temperature. We monitored the incubation behaviour of nine sandpiper species using thermologgers at 15 arctic sites between 2016 and 2019. We also used thermologgers to record the ground surface temperature at conspecific nest sites and extracted NDVI values from a remote sensing product. We found no relationship between either environmental variables and biparental incubation behaviour. Conversely, as ground-surface temperature increased, uniparental species decreased total duration of recesses (TDR) and mean duration of recesses (MDR), but increased number of recesses (NR). Moreover, small species showed stronger relationships with ground-surface temperature than large species. When all uniparental species were combined, an increase in NDVI was correlated with higher mean duration, total duration and number of recesses, but relationships varied widely across species. Finally, some uniparental species showed a lag effect with a higher nest attentiveness after a warm day while more recesses occurred after a cold day than was predicted based on current temperatures. We demonstrate the complex interplay between shorebird incubation strategies, incubation behaviour, and environmental conditions. Understanding how species respond to changes in their environment during incubation helps predict their future reproductive success.

Arctic plants are affected by many stressors. Root-associated fungi are thought to influence plant performance in stressful environmental conditions. However, the relationships are not transparent; do the number of fungal partners, their ecological functions and community composition mediate the impact of environmental conditions and/or influence host plant performance? To address these questions, we used a common arctic plant as a model system: Bistorta vivipara. Whole plants (including root system) were collected from nine locations in Spitsbergen (n=214). Morphometric features were measured as a proxy for performance and combined with metabarcoding datasets of their root-associated fungi (amplicon sequence variants, ASVs), edaphic and meteorological variables. Seven biological hypotheses regarding fungal influence on plant measures were tested using structural equation modelling. The best-fitting model revealed that local temperature affected plants both directly (negatively aboveground and positively below-ground) and indirectly - mediated by fungal richness and the ratio of symbio- and saprotrophic ASVs. Fungal community composition did not impact plant measurements and plant reproductive investment did not depend on any fungal parameters. The lack of impact of fungal community composition on plant performance suggests that the functional importance of fungi is more important than their identity. The influence of temperature on host plants is therefore complex and should be examined further.

1. Increasing populations of mesopredators are suspected to cause declines in vulnerable wildlife to the extent that mesopredator decimation actions (culling) have become commonplace. Design constraints, especially a lack of spatial replication, often hamper the assessment of the impact of such actions. However, extensive temporal replication (i.e. time series) and accounting for potentially confounding variables may alleviate this problem. 2. In alpine-arctic tundra, the red fox Vulpes vulpes is increasing, while many bird species are declining, likely due to increased predation. Here, we assessed the impact of a long-term (12-year) and spatially extensive (~3,500 km2) red fox culling action on the red-listed willow ptarmigan Lagopus lagopus in the Norwegian Arctic. Ptarmigan populations were monitored annually in the impact area and in an adjacent no-action area, including a 5-year period before the action commenced. While logistical constraints prohibited monitoring of red fox population densities, the number of culled foxes and three influential food web covariates were monitored after the onset of the culling action. 2. A Before-After-Control-Impact-Paired-Series (BACIPS) analysis without food web covariates indicated that red fox culling curbed the decline of the population in the impact area, and that ptarmigan population density became ~25% higher than in the reference area. 4. Spatially and temporally variable drivers within the food web confounded the simple BACIPS analysis. Accounting for three food web drivers as covariates in a linear mixed model after the onset of action, yielded a more unbiased impact estimate that amounted to ~40% higher ptarmigan population density (4.3 more ptarmigan/km2) in the red fox impact area. 5. Synthesis and applications. We provide the first evidence of the role of the recent expansion of red fox in the decline of bird populations in tundra. We also show that red fox culling may be able to curb such declines, given that management actions are large scale and long term. As mesopredator culling campaigns are often expensive and controversial, it is important that their impacts are accurately assessed. We demonstrate that the accuracy of impact assessments can be profoundly increased by monitoring drivers of food web dynamics that impinge on the target species so that such drivers can be included as covariates in the analysis. This applies in particular to declining bird populations in boreal and arctic food webs ruled by strong multi-annual interaction cycles.

Understanding the dynamics of biodiversity in the past will contribute to a better informed inference of future biodiversity. Palaeoecological patterns in biodiversity are mainly preserved in natural archives such as lake sediments. Using ancient DNA from the sediment of 10 lakes from northern Fennoscandia, we analysed terrestrial plant diversity pattern for the entire Holocene, and how these patterns correspond to drivers of change such as temperature and biota. We modeled temporal trends in taxonomic richness and turnover using generalized additive models (GAM). We included delta oxygen isotope values from North Greenland Ice Core Project as a proxy for regional temperature, and the presence of dominant woody species as biotic drivers of terrestrial plant diversity. Results show a general tendency of an increase in species richness from the early Holocene onwards, but this pattern is asynchronous across the lakes, with some lakes having a peak in diversity in the mid-Holocene (8,000-6,000 cal. BP), late Holocene (~2,500 cal. BP), or in recent times. The turnover decreases in most of the lakes throughout the Holocene. Meanwhile, it consistently increases in a few lakes. With some exceptions, temperature and biotic variable differentially affects the richness and turnover across the lakes. Our study from multiple lakes and heterogeneous habitats may be able to identify the main drivers of past biodiversity changes in these systems. As a result, it may help us to understand the mechanisms of change so that the impacts of current climate change and biotic factors on biodiversity may be assessed. Author's list and affiliations:Dilli Prasad Rijal1, Peter D. Heintzman2, Youri Lammers2, Nigel Gilles Yoccoz1, Tony Gavin Brown2,3, Kelsey Lorberau1, Dorothee Ehrich1, Iva Pitelkova2, Tomasz Goslar4, Jostein Bakke5, Kari Anne Bråthen1, Inger Greve Alsos21Department of Arctic and Marine Biology, UiT - The Arctic University of Norway, NO-9037 Tromsø, Norway.2The Arctic University Museum of Norway, UiT - The Arctic University of Norway, NO-9037 Tromsø, Norway.3School of Geography and Environmental Science, University of Southampton, Highfield, Southampton, SO17 1BJ, UK.44Faculty of Physics, Adam Mickiewicz University, Poznan, Poland5Department of Earth Science, University of Bergen, 5020 Bergen, Norway

Loss of Arctic sea ice owing to climate change is predicted to reduce both genetic diversity and gene flow in ice-dependent species, with potentially negative consequences for their long-term viability. Here, we tested for the population-genetic impacts of reduced sea ice cover on the polar bear (Ursus maritimus) sampled across two decades (1995–2016) from the Svalbard Archipelago, Norway, an area that is affected by rapid sea ice loss in the Arctic Barents Sea. We analysed genetic variation at 22 microsatellite loci for 626 polar bears from four sampling areas within the archipelago. Our results revealed a 3–10% loss of genetic diversity across the study period, accompanied by a near 200% increase in genetic differentiation across regions. These effects may best be explained by a decrease in gene flow caused by habitat fragmentation owing to the loss of sea ice coverage, resulting in increased inbreeding of local polar bears within the focal sampling areas in the Svalbard Archipelago. This study illustrates the importance of genetic monitoring for developing adaptive management strategies for polar bears and other ice-dependent species.

Run to the hills : gene flow among mountain areas leads to low genetic differentiation in the Norwegian lemming

This review provides a synopsis of the main findings of individual papers in the special issue Terrestrial Biodiversity in a Rapidly Changing Arctic. The special issue was developed to inform the State of the Arctic Terrestrial Biodiversity Report developed by the Circumpolar Biodiversity Monitoring Program (CBMP) of the Conservation of Arctic Flora and Fauna (CAFF), Arctic Council working group. Salient points about the status and trends of Arctic biodiversity and biodiversity monitoring are organized by taxonomic groups: (1) vegetation, (2) invertebrates, (3) mammals, and (4) birds. This is followed by a discussion about commonalities across the collection of papers, for example, that heterogeneity was a predominant pattern of change particularly when assessing global trends for Arctic terrestrial biodiversity. Finally, the need for a comprehensive, integrated, ecosystem-based monitoring program, coupled with targeted research projects deciphering causal patterns, is discussed.

This is the pre-peer reviewed version of the following article: Urbani, Tryland, Ehrich, Fuglei, Battilani, Balboni. Ancient origin and genetic segregation of canine circovirus infecting arctic foxes (Vulpes lagopus) in Svalbard and red foxes (Vulpes vulpes) in Northern Norway. Transboundary and Emerging Diseases. 2020;00:1-11, which has been published in final form at https://doi.org/10.1111/tbed.13783. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions. Canine circovirus (CanineCV) is a relatively new viral species, belonging to the family Circoviridae, whose pathogenic role is still uncertain. Since its first description in one domestic dog in 2011 from the USA, several reports have been documenting its distribution worldwide. Recently, CanineCV was also detected in wild animals such as wolves, foxes and badgers. In order to investigate the presence and the genetic characteristics of CanineCV in foxes of Arctic and Sub‐Arctic regions, the presence of CanineCV DNA in internal organs (liver and spleen) of 51 arctic foxes (Vulpes lagopus) from Svalbard archipelago and 59 red foxes (Vulpes vulpes) from Northern Norway, sampled from 1996 to 2001 and from 2014 to 2018, respectively, was screened by real‐time PCR. CanineCV was detected in 11/51 arctic foxes and in 10/59 red foxes, backdating the circulation of the virus at least to 1996 in the arctic fox population. The complete genome of 14 identified CanineCV was sequenced and analysed showing an identity higher than 80.8% with the reference strains available to date. According to the species demarcation threshold of 80% genome‐wide nucleotide sequence identity for members of the family Circoviridae provided by International Committee on Taxonomy of Viruses (ICTV), all the CanineCV belong to a single species. Phylogenetic analysis revealed that all the CanineCV were subdivided into five main clusters with one including only CanineCV identified in foxes. Furthermore, CanineCV identified in arctic foxes and red foxes formed two distinct lineages. From these data, we hypothesize that the viral transmission did not occur between the two species of foxes as a consequence of the lack of contact between the two hosts or that the virus acquired mutations in the time elapsed between the samplings.

Rapid climate change is threatening the stability and functioning of Arctic ecosystems. As the Arctic warms, shrubs have been widely observed to expand, which has potentially serious consequences for global climate regulation and for the ecological processes characterising these ecosystems. However, it is currently unclear why this shrubification has been spatially uneven across the Arctic, with herbivory being suggested as a key regulating factor. By taking advantage of freely available satellite imagery spanning three decades, we mapped changes in shrub cover in the Yamal Peninsula and related these to changes in summer temperature and reindeer population size. We found no evidence that shrubs had expanded in the study site, despite increasing summer temperatures. At the same time, herbivore pressure increased significantly, with the local reindeer population size growing by about 75%. Altogether, our results thus point towards increases in large herbivore pressure having compensated for the warming of the Peninsula, halting the shrubification of the area. This suggests that strategic semi-domesticated reindeer husbandry, which is a common practice across the Eurasian Arctic, could represent an efficient environmental management strategy for maintaining open tundra landscapes in the face of rapid climate change.

This is a pre-copyedited, author-produced version of an article accepted for publication in The Auk following peer review. The version of record, Pokrovsky, I.G., Ehrich, D., Fufachev, I.A., Ims, R.A., Kulikova, O., Sokolov, A., ... Yoccoz, N.G. (2020). Nest association between two predators as a behavioral response to the low density of rodents. The AUK, 137(1), ukz060, is available online at: https://doi.org/10.1093/auk/ukz060. Many birds nest in association with aggressive birds of other species to benefit from their protection against predators. We hypothesized that the protective effect also could extend to foraging resources, whereby the resultant resource-enriched habitats near a nest of aggressive raptors could be an alternative cause of associations between nesting bird species with non-overlapping foraging niches. In the Arctic, the Rough-legged Hawk (Buteo lagopus) and the Peregrine Falcon (Falco peregrinus) are 2 raptor species with non-overlapping food resources that have been reported to nest sometimes in close proximity. Since nesting Peregrine Falcons are very aggressive, they may protect the small rodent prey near their nests from predation, and Rough-legged Hawks could use these hot spots as a nesting territory. In 2 regions in low Arctic Russia we found that (1) the nesting territories of Peregrine Falcons were indeed enriched with small rodents as compared to control areas, (2) the probability of nest association between the 2 raptors increased when rodent abundance was generally low in the region where hawks did not use alternative prey, and (3) hawk reproductive success increased when nesting close to Peregrine Falcons. These results suggest that implications of aggressive nest site defense in birds in certain cases may involve more mechanisms than previously explored. A key ecological process in tundra, rodent population cycles, may explain the occurrence and adaptive significance of a specific behavior pattern, the nesting association between 2 raptor species.

Invertebrate herbivores depend on external temperature for growth and metabolism. Continued warming in tundra ecosystems is proposed to result in increased invertebrate herbivory. However, empirical data about how current levels of invertebrate herbivory vary across the Arctic is limited and generally restricted to a single host plant or a small group of species, so predicting future change remains challenging. We investigated large-scale patterns of invertebrate herbivory across the tundra biome at the community level and explored how these patterns are related to long-term climatic conditions and year-of-sampling weather, habitat characteristics, and aboveground biomass production. Utilizing a standardized protocol, we collected samples from 92 plots nested within 20 tundra sites during summer 2015. We estimated the community-weighted biomass lost based on the total leaf area consumed by invertebrates for the most common plant species within each plot. Overall, invertebrate herbivory was prevalent at low intensities across the tundra, with estimates averaging 0.94% and ranging between 0.02 and 5.69% of plant biomass. Our results suggest that mid-summer temperature influences the intensity of invertebrate herbivory at the community level, consistent with the hypothesis that climate warming should increase plant losses to invertebrates in the tundra. However, most of the observed variation in herbivory was associated with other site level characteristics, indicating that other local ecological factors also play an important role. More details about the local drivers of invertebrate herbivory are necessary to predict the consequences for rapidly changing tundra ecosystems. - 2019, Springer-Verlag GmbH Germany, part of Springer Nature. This study is a contribution of the Herbivory Network ( https://herbivory.lbhi.is ). SIR and DSH were supported by the Natural Sciences and Engineering Research Council of Canada (RGPNS-305471); ICB was supported by a postdoctoral fellowship funded by the Icelandic Research Fund (Rannsóknasjóður, Grant nr 152468–051) and AXA Research Fund (15-AXA-PDOC-307); JMA was supported by Carl Tryggers Stiftelse för Vetenskaplig Forskning (Sweden) and Qatar Petroleum; MVK and VZ were supported by the Academy of Finland (Project 276671); AS and NS were supported by the Grant of Russian fund for basic research (18-05-60261); Field work on Bylot Island was supported by the Natural Sciences and Engineering Research Council of Canada, the network of Center of excellence ArcticNet, and the Polar Continental Shelf Program to GG and EL; SK and the Burntpoint Creek Research Station was supported by the Waterfowl, Wetlands and Far North research unit of the Ontario Ministry of Natural Resources and Forestry, with assistance from K. Bennet, R. Brook, and L. Pollock; O. Krasheninnikova assisted with the collection plant samples on Erkuta; SS was partly supported by a state assignment of the Institute of Plant and Animal Ecology UB RAS; DDE was supported by a Grant to JO from the Swedish Research Council Formas 2012–1039, 2012–230, 2015–1091 and a Grant to DDE from Gunnar and Ruth Björkmans fund for botanical research in northern Sweden; Sampling in Svalbard was conducted during an UNIS field course (ISJ); JSP was supported by the WSL Institute for Snow and Avalanche Research, and an INTERACT Transnational Access Research Grant; Research at Toolik Field Station by ALA was supported by National Science Foundation Grants DEB 102683 to support the Arctic LTER and OPP 0908502; JDMS was supported by the Research Council of Norway (262064); C. Brachmann assisted with Fig. 1 ; H.C. Proctor and B.A. Keddie assisted with gall damage determination. Scopus

Plant-herbivore relationships are important for the functioning of tundra ecosystems. Here, we report the first results from an exclosure experiment that, something very few studies have done, separated the impact of three sizes of herbivores (small, medium and large) on nine functional groups of plants in the low arctic tundra of the Yamal Peninsula (Russia). Herbivore faeces counts in the exclosures and pictures from automatic cameras proved that the experimental setup worked. The majority of plant groups did not respond to exclusion of herbivores, supporting our expectation that vegetation responses in tundra are generally too slow to be measured during one growing season. The plant groups with highest growth rates and palatability (forbs and grasses) increased their biomass in meadows associated to tall willow shrubs when reindeer were excluded. This result was expected based on studies from other arctic regions. Our results also suggested that willow meadows and forb tundra, which are focal habitat for herbivores, are resilient and have the capacity to increase their biomass over a short term. We expect this experiment to provide valuable information on how different plant functional types and habitats with different growing conditions and importance to herbivores respond to relaxed grazing pressure from a variety of tundra herbivores.

Compilation of the species richness data was made possible through the TFI Networks grant to CD, “Effect Studies and Adaptation to Climate Change,” under the Norforsk initiative (2011 – 2014) which supported two CBIONET-AVA workshops held in Denmark during 2013. The genetic studies were funded by the Research Council of Norway (grant nos. 150322/720 and 170952/V40 to CB).

Published version available at https://doi.org/10.1007/s00035-015-0162-2. The naturally fragmented habitat on the tallest African mountains provides a good model system to study vicariance, dispersal, and hybridization. Many mountains are separated by lowland that likely was unsuitable for high-alpine plants even during cold climatic periods. We explore the relative importance of these processes using two endemic sister species: the widespread Ethiopian/eastern East African Carex monostachya and the mainly western East African C. runssoroensis. These bog-forming sedges co-occur in some mountains and are hypothesized to hybridize. The two species were distinctly differentiated for genome-wide Amplified Fragment Length Polymorphisms (AFLPs), also in one mountain where they co-occur. However, the plants from another mountain showed strong signals of admixture. The results suggest initial divergence into one western and one northern/eastern lineage, followed by long-distance dispersal resulting in secondary contact zones. Also within species genetic diversity was clearly structured with distinct genetic groups on some, but not all mountains. Differentiation levels varied considerably and did not always correspond to the extent of lowland habitat between mountains. The narrow Rift Valley in the otherwise nearly contiguous highlands in Ethiopia appears to present a much stronger barrier to dispersal than the extensive lowlands separating Ethiopia from East Africa. This may be a general pattern since it has been documented also for other afro-alpine species