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We report predation by an Arctic Fox Alopex lagopus on two seabird species, Atlantic Puffins Fratercula arctica and Leach's Storm Petrels Hydrobates leucorhous, nesting on Bakeapple Island, Little Fogo Islands, Newfoundland, Canada. This event took place in 2022, when a whole-island inspection revealed that fox, facilitated by over-ice invasion, killed at least 139 adult storm petrels and 8 puffin chicks. The fox also dug out 83 storm petrel and 4 puffin burrows. Breeding by seabirds on the island, which harbours some of the northernmost colonies in Newfoundland, was also largely disrupted; we documented extremely low egg and chick production values associated with the fox's presence and activity. We discuss the implications of such events for local seabird populations and the need for long-term monitoring to fully understand the impact of these predation events. [ABSTRACT FROM AUTHOR]

Indirect interactions are widespread among prey species that share a common predator, but the underlying mechanisms driving these interactions are often unclear, and our ability to predict their outcome is limited.Changes in behavioural traits that impact predator space use could be a key proximal mechanism mediating indirect interactions, but there is little empirical evidence of the causes and consequences of such behavioural‐numerical response in multispecies systems.Here, we investigate the complex ecological relationships between seven prey species sharing a common predator. We used a path analysis approach on a comprehensive 9‐year data set simultaneously tracking predator space use, prey densities and prey mortality rate on key species of a simplified Arctic food web.We show that high availability of a clumped and spatially predictable prey (goose eggs) leads to a twofold reduction in predator (arctic fox) home range size, which increases local predator density and strongly decreases nest survival of an incidental prey (American golden plover). On the contrary, a scattered cyclic prey with potentially lower spatial predictability (lemming) had a weaker effect on fox space use and an overall positive impact on the survival of incidental prey.These contrasting effects underline the importance of studying behavioural responses of predators in multiprey systems and to explicitly integrate behavioural‐numerical responses in multispecies predator–prey models. [ABSTRACT FROM AUTHOR]

To gain better insight into the cascading impact of warming-induced changes in the physical landscape on biodiversity, it is crucial to establish stronger links between abiotic and ecological processes governing species distribution. Abiotic processes shaping the physical characteristics of the environment could significantly influence predator movements in the landscape and ultimately affect biodiversity through interspecific interactions. In the Arctic tundra, the main terrestrial predator (Arctic fox) avoids patches of wetlands composed of ponds with islets that can act as refuges for prey. Little is known about the geomorphological processes generating islets selected by prey species. Our study aimed to identify i) the physical characteristics of islets selected by Arctic-nesting birds and ii) the geomorphological processes generating islets available in the landscape. Over two breeding seasons, we determined the occurrence of nesting birds (Glaucous gull, Cackling goose, Red-throated loon) on islets (N=396) found over a 150 km2 area on Bylot Island (Nunavut, Canada). Occupied islets were located further away from the shore (10.6 m ± 7.3 vs 7.4 m ± 6.8) and surrounded by deeper water (33.6 cm ± 10.6 vs 28.1 cm ± 11.5). As expected, all three bird species selected islets less accessible to Arctic foxes, with nesting occurrence increasing (linearly or nonlinearly) with distance to shore and/or water depth around islets. Based on high-resolution satellite image and field observations, we found that ice-wedge polygon degradation generated the majority of islets (71 %) found in the landscape. Those islets were on average farther from the shore and surrounded by deeper water than those generated by other processes. As polygon degradation is projected to accelerate in response to warming, new refuges will likely emerge in the Arctic landscape, but current refuges could also disappear. Changes in the rate of polygon degradation may thus affect Arctic tundra biodiversity by altering predator-prey interactions. [ABSTRACT FROM AUTHOR]

Egg predation is the primary cause of nest failure for tundra nesting birds. Taverner's Cackling Geese (Branta hutchinsii taverneri) breeding on the North Slope of Alaska have increased approximately 5-fold over the last 25 years and are now one of the most encountered waterbird species breeding at our study site on the coastal plain of Arctic National Wildlife Refuge. This rapid population growth may offer a new food resource for egg predators, impacting predator populations, which in turn could have cascading effects for other tundra nesting bird species, many of which are declining. To determine how the population growth of geese may affect the nest-predator community, and to establish a baseline of predators as the area is impacted by climate change and development, we used digital time-lapse cameras to record predation events at Cackling Goose nests. We determined fate for 52 nests in 2017, 2019, and 2021, of which 20 were depredated. The most frequent predator differed each year. Red foxes (Vulpes vulpes) were responsible for 89% of depredations in 2017 and wolverines (Gulo gulo) for 67% in 2019, and those species only depredated nests in those single years. In contrast, Arctic foxes (Vulpes lagopus) were responsible for nest failure in all years, but did not exceed 40% of total depredations in any year. Golden Eagles (Aquila chrysaetos) were an unexpected egg predator, depredating 2 nests. Our results were notably different than work on other Arctic goose species, where Arctic foxes were the primary predator. The inter-annual variability of egg predators at this Arctic Refuge study site provides insights into complex predator–prey interactions on the Arctic Coastal Plain. La depredación de huevos es la causa primaria del fracaso de nido para aves que anidan en la tundra. El ganso Branta hutchinsii taverneri, que se reproduce en la pendiente Norte de Alaska ha quintuplicado su presencia en los últimos 25 años y ahora es una de las especies acuáticas en reproducción más observadas en nuestro sitio de estudio en la planicie costera del Arctic National Wildlife Refuge. Este crecimiento poblacional acelerado puede ofrecer una nueva fuente de alimentación para depredadores de huevos, impactando las poblaciones de depredadores, que podría tener efectos en cascada en otras especies de aves que anidan en la tundra, muchas en declive. Para determinar cómo el crecimiento poblacional de gansos puede afectar la comunidad de depredadores de nidos y establecer una línea base de depredadores en un área que es impactada por el cambio climático y el desarrollo, usamos cámaras digitales con temporizador automático para registrar eventos de depredación en nidos de ganso Branta hutchinsii. Determinamos el destino de 52 nidos en 2017, 2019 y 2021, de los cuales 20 fueron depredados. El depredador más frecuente varió cada año. Los zorros rojos (Vulpes vulpes) fueron responsables del 89% de las depredaciones en el 2017, mientras que los glotones (Gulo gulo) lo fueron del 67% en el 2019, y esas especies solo depredaron nidos en esos años. En contraste, el zorro artico (Vulpes lagopus) fue responsable de fracaso de anidación durante todos los años, pero su cuota de depredación no excedió el 40% en ninguno de los años. El águila real (Aquila chrysaetos) fue un depredador inesperado, depredando 2 nidos. Nuestros resultados fueron notablemente diferentes que otros estudios con otras especies de gansos silvestres del Artico, donde los zorros articos fueron los depredadores primarios. La variación interanual de depredadores de huevos en este sitio de estudio en el Refugio Artico proporciona información en interacciones complejas depredador-presa en la Planicie Costera Artica. Palabras clave: cámaras para vida silvestre, depredador de huevos, ganso Branta hutchinsii taverneri, gansos de anidación artica, Planicie Costera Artica. [ABSTRACT FROM AUTHOR]

The strength of indirect biotic interactions is difficult to quantify in the wild and can alter community composition. To investigate whether the presence of a prey species affects the population growth rate of another prey species, we quantified predator-mediated interaction strength using a multi-prey mechanistic model of predation and a population matrix model. Models were parametrized using behavioural, demographic and experimental data from a vertebrate community that includes the arctic fox (Vulpes lagopus), a predator feeding on lemmings and eggs of various species such as sandpipers and geese. We show that the positive effects of the goose colony on sandpiper nesting success (due to reduction of search time for sandpiper nests) were outweighed by the negative effect of an increase in fox density. The fox numerical response was driven by changes in home range size. As a result, the net interaction from the presence of geese was negative and could lead to local exclusion of sandpipers. Our study provides a rare empirically based model that integrates mechanistic multi-species functional responses and behavioural processes underlying the predator numerical response. This is an important step forward in our ability to quantify the consequences of predation for community structure and dynamics. [ABSTRACT FROM AUTHOR]

Boldness is an important trait in wild populations, and among-individual differences can link to individual fitness. The strength and direction of relationships between behavioral and life-history traits may however vary according to environmental conditions, where fluctuating selection acting on behavioral traits contributes to the maintenance of personality differences. We explored sources of variation in Arctic fox (Vulpes lagopus) boldness and investigated how temporal variation in the abundance of a main prey (lemmings) influences the relationship between fox boldness and reproductive success. We measured the behavioral reaction of individuals when escaping after handling, as an indicator of their boldness. We obtained 70 measurements from 42 individuals during two years of low lemming abundance and 2 years of high lemming abundance and assessed fox litter size as an indicator of reproductive success. First, individual characteristics (age, sex, mass) did not affect Arctic fox boldness, while individual identity generated variation in boldness. Next, we found that during years of low lemming density, individuals behaving boldly had more pups than those behaving less boldly, suggesting boldness may provide an advantage when lemmings are scarce by increasing hunting success or allowing access to alternative resources. However, all individuals tended to show high levels of boldness when lemming density was high, and all produced large litters. Temporal variation in the abundance of a main prey might therefore influence the relation between boldness and reproductive success of a predator, and if individuals consistently differ in their level of boldness, fluctuating selection could contribute to the maintenance of personality. Significance statement: Effects of boldness on Arctic fox reproductive success: lemming abundance matters! When lemmings are scarce, foxes showing bold behavior have more pups than foxes showing less bold behavior. This highlights that under low prey availability, boldness may bring short-term benefits to predators, potentially because it allows to acquire more food. When lemmings are abundant, however, all foxes produce as many pups. This shows that environmental conditions such as prey abundance can influence the relation between behavior and reproductive success in a predator. Studying the context-dependency of relationships between behavior and reproductive success is critical to better understand ecological and evolutionary consequences of environmental change. [ABSTRACT FROM AUTHOR]

Resource fluctuation is a major driver of animal movement, influencing strategic choices such as residency vs nomadism, or social dynamics. The Arctic tundra is characterized by strong seasonality: Resources are abundant during the short summers but scarce in winters. Therefore, expansion of boreal‐forest species onto the tundra raises questions on how they cope with winter‐resource scarcity. We examined a recent incursion by red foxes (Vulpes vulpes) onto the coastal tundra of northern Manitoba, an area historically occupied by Arctic foxes (Vulpes lagopus) that lacks access to anthropogenic foods, and compared seasonal shifts in space use of the two species. We used 4 years of telemetry data following 8 red foxes and 11 Arctic foxes to test the hypothesis that the movement tactics of both species are primarily driven by temporal variability of resources. We also predicted that the harsh tundra conditions in winter would drive red foxes to disperse more often and maintain larger home ranges year‐round than Arctic foxes, which are adapted to this environment. Dispersal was the most frequent winter movement tactic in both fox species, despite its association with high mortality (winter mortality was 9.4 times higher in dispersers than residents). Red foxes consistently dispersed toward the boreal forest, whereas Arctic foxes primarily used sea ice to disperse. Home range size of red and Arctic foxes did not differ in summer, but resident red foxes substantially increased their home range size in winter, whereas home range size of resident Arctic foxes did not change seasonally. As climate changes, abiotic constraints on some species may relax, but associated declines in prey communities may lead to local extirpation of many predators, notably by favoring dispersal during resource scarcity. [ABSTRACT FROM AUTHOR]

Dedicated conservation efforts spanning the past two decades have saved the Fennoscandian Arctic fox (Vulpes lagopus) population from local extinction, and extensive resources continue to be invested in the species' conservation and management. Although increasing, populations remain isolated, small and are not yet viable in the longer term. An understanding of causes of mortality are consequently important to optimize ongoing conservation actions. Golden eagles (Aquila chrysaetos) are a predator of Arctic foxes, yet little information on this interaction is available in the literature. We document and detail six confirmed cases of Golden eagle depredation of Arctic foxes at the Norwegian captive breeding facility (2019–2022), where foxes are housed in large open‐air enclosures in the species' natural habitat. Here, timely detection of missing/dead foxes was challenging, and new insights have been gained following recently improved enclosure monitoring. Golden eagle predation peaked during the winter months, with no cases reported from June to November. This finding contrasts with that which is reported from the field, both for Arctic and other fox species, where eagle depredation peaked at dens with young (summer). While the seasonality of depredation may be ecosystem specific, documented cases from the field may be biased by higher survey efforts associated with the monitoring of reproductive success during the summer. Both white and blue color morphs were housed at the breeding station, yet only white foxes were preyed upon, and mortality was male biased. Mitigation measures and their effectiveness implemented at the facility are presented. Findings are discussed in the broader Arctic fox population ecology and conservation context. [ABSTRACT FROM AUTHOR]

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.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.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.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.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. [ABSTRACT FROM AUTHOR]

Arctic foxes are significant predators of pups in lairs in much of the geographic range of ringed seals (Smith, [25]; Smith et al., [29]). Arctic fox predation of ringed seals occurs on pups at lairs in spring (Smith, [25], [26]; Smith & Lydersen, [30]; Stirling, [32]; Stirling & Archibald, [33]). During unusual warm temperatures and rain events on southeast Baffin Island in April 1972, lairs collapsed prematurely and pups exposed in their subnivean lairs experienced elevated rates of bear and fox predation (Stirling & Smith, [35]). During spring, polar bear predation of ringed seals in the fast ice is focused on pups in lairs (Smith, [25], [26]; Smith & Lydersen, [30]; Stirling, [32]; Stirling & Archibald, [33]). [Extracted from the article]

Behavioral ecology, Cyprinus carpio, diet, feeding behavior, fish, predation, Vulpes vulpes, canids, mammalian predators Keywords: behavioral ecology; canids; Cyprinus carpio; diet; feeding behavior; fish; mammalian predators; predation; Vulpes vulpes EN behavioral ecology canids Cyprinus carpio diet feeding behavior fish mammalian predators predation Vulpes vulpes 1 4 4 12/05/22 20221201 NES 221201 The red fox ( I Vulpes vulpes i ) is a mesocarnivore species that exploits opportunistically a wide range of prey items that are consumed as a function of their abundance and availability (Díaz-Ruiz et al., [3]). " Biogeographical Patterns in the Diet of an Opportunistic Predator: The Red Fox Vulpes vulpes in the Iberian Peninsula.". [Extracted from the article]

Prey handling processes are considered a dominant mechanism leading to short‐term positive indirect effects between prey that share a predator. However, a growing body of research indicates that predators are not necessarily limited by such processes in the wild. Density‐dependent changes in predator foraging behavior can also generate positive indirect effects but they are rarely included as explicit functions of prey densities in functional response models. With the aim of untangling proximate mechanisms of species interactions in natural communities and improving our ability to quantify interaction strength, we extended the multi‐prey version of the Holling disk equation by including density‐dependent changes in predator foraging behavior. Our model, based on species traits and behavior, was inspired by the vertebrate community of the arctic tundra, where the main predator (the arctic fox) is an active forager feeding primarily on cyclic small rodent (lemming) and eggs of various tundra‐nesting bird species. Short‐term positive indirect effects of lemmings on birds have been documented over the circumpolar Arctic but the underlying mechanisms remain poorly understood. We used a unique data set, containing high‐frequency GPS tracking, accelerometer, behavioral, and experimental data to parameterize the multi‐prey model, and a 15‐year time series of prey densities and bird nesting success to evaluate interaction strength between species. We found that (1) prey handling processes play a minor role in our system and (2) changes in arctic fox daily activity budget and distance traveled can partly explain the predation release on birds observed during lemming peaks. These adjustments in predator foraging behavior with respect to the main prey density thus appear as the dominant mechanism leading to positive indirect effects commonly reported among arctic tundra prey. Density‐dependent changes in functional response components have been little studied in natural vertebrate communities and deserve more attention to improve our ability to quantify the strength of species interactions. [ABSTRACT FROM AUTHOR]

Colonial nesting is associated with numerous costs and benefits that may either increase or decrease fitness of individuals in colonies. Fitness can vary as a function of the location within colonies and individuals may attempt to improve their fitness by changing their nesting location between years. We used a 24 year data set on nest locations within the Tutakoke River Black Brant (Branta bernicla nigricans) colony on the Yukon-Kuskokwim Delta in western Alaska and multi-state capture-mark-recapture models to study the movement of individuals between 2 spatial strata in the colony separated by the Tutakoke River. We found that individuals nesting in a stratum that experienced higher levels of predation by arctic foxes (Vulpes lagopus) were 3 times more likely to move to the other stratum than vice versa, despite slightly higher risk of tidal flooding in the second stratum. These results suggest that Black Brant changed nest locations in an attempt to maximize reproductive fitness and they are consistent with a long-term shift in nest density over the course of the study. La anidación en colonias está asociada con numerosos costos y beneficios que pueden aumentar o reducir la sobrevivencia de individuos en colonias. La sobrevivencia puede variar en función de la localización del nido al interior de la colonia y los individuos pueden intentar mejoras en su sobrevivencia mediante el cambio de sitio de anidación en diferentes años. Usamos un juego de datos de localización de nidos de 24 años en la colonia de gansos Branta bernicla nigricans del río Tutakoke en el delta del Yukon-Kuskokwin en el occidente de Alaska y modelos multiestado de capura-marcado-recaptura para estudiar el movimiento de individuos entre 2 estratos espaciales en la colonia separados por el río Tutakoke. Encontramos que los individuos anidando en un estrato que experimentó mayores niveles de depredación por zorros del Ártico (Vulpes lagopus) tenían una probabilidad 3 veces mayor de moverse al otro estrato que viceversa, aún pese a un ligeramente mayor riesgo de inundación por mareas en el segundo estrato. Estos resultados sugieren que estos gansos cambiaron la ubicación de sus nidos para intentar maximizar su sobrevivencia reproductiva y son consistentes con un cambio a largo plazo en la densidad de nidos a largo plazo a lo largo del periodo de este estudio. Palabras clave: ártico, colonialidad, dispersión, ganso, información privada, información pública, multi-estado. [ABSTRACT FROM AUTHOR]

In socially flexible species, the tendency to live in groups is expected to vary through a trade-off between costs and benefits, determined by ecological conditions. The Resource Dispersion Hypothesis predicts that group size changes in response to patterns in resource availability. An additional dimension is described in Hersteinsson's model positing that sociality is further affected by a cost–benefit trade-off related to predation pressure. In the arctic fox (Vulpes lagopus), group-living follows a regional trade-off in resources' availability and intra-guild predation pressure. However, the effect of local fluctuations is poorly known, but offers an unusual opportunity to test predictions that differ between the two hypotheses in systems where prey availability is linked to intra-guild predation. Based on 17-year monitoring of arctic fox and cyclic rodent prey populations, we addressed the Resource Dispersion Hypothesis and discuss the results in relation to the impact of predation in Hersteinsson's model. Group-living increased with prey density, from 7.7% (low density) to 28% (high density). However, it remained high (44%) despite a rodent crash and this could be explained by increased benefits from cooperative defence against prey switching by top predators. We conclude that both resource abundance and predation pressure are factors underpinning the formation of social groups in fluctuating ecosystems. [ABSTRACT FROM AUTHOR]

We propose an ecogenetic model of "prey–predator" community with predator fitness determined genetically by a single autosomal diallelic pleiotropic locus in the case of diploid population. Predator genotypes with different reproductive potential are unequally adapted to food resource limitation; therefore, the fitness of a predator's genotype is determined by not only its own genotype but also the prey numbers. We use discrete-time equations for modeling, which allows considering features of the community species lifecycle. The paper extends our previous studies modeling evolution of a local population to explain existing genetic diversity by litter size in various (natural and farmed) populations of Arctic foxes (Alopex lagopus). Direct inclusion of prey population dynamics in the model of community allows analyzing polymorphism maintenance in arctic fox populations under more realistic conditions. As in simpler models, the direction of evolution of the predator population is shown to be generally determined by the relative position of its genotype fitnesses, whereas the parameter set characterizing birth rates of the prey and the predator, as well as the characteristics of interspecific interaction, determines the dynamic mode of interacting species numbers. However, even without overdominance, a predator can maintain a stable polymorphism owing to large-amplitude fluctuations in the number of prey, which change the direction of natural selection in the predator population. Different dynamics in the genetic composition of the predator can lead to a change in the dynamic mode of the prey numbers. [ABSTRACT FROM AUTHOR]

Climate-caused changes in prey abundance may alter predator–prey dynamics in the Arctic food web. Lemmings (Dicrostonyx spp.) are important prey for Arctic foxes (Vulpes lagopus) and their annual population fluctuations drive fox reproduction, creating strongly linked predator–prey population cycles. Winter diet directly impacts Arctic fox reproductive success, but winter prey diversity on the tundra is low. Strategies such as using the marine environment to scavenge seals have allowed Arctic foxes to persist during years of low lemming abundance. However, warming winters have decreased snowpack quality, preventing lemmings from reaching their previous high abundances, which may reduce their impact on predator dynamics. We investigated Arctic fox dietary response to lemming abundance by reconstructing Arctic fox winter diet in the low Arctic. Next-generation sequencing of fecal DNA, from samples (n = 627) collected at dens in winters of 2011–2018, identified prey both from terrestrial and marine environments. Despite lemming cycle damping, Arctic foxes still increased lemming consumption during years of higher lemming abundance. Alternative prey such as marine resources were consumed more during years of low lemming abundance, with up to 45% of samples containing marine resources in low lemming years. In addition, Arctic foxes consumed high proportions of meadow voles (Microtus pennsylvanicus), which may represent a new alternative prey, suggesting climate change may be creating new foraging opportunities. Changes in prey abundance illustrate how climate-caused disturbances are altering Arctic food-web dynamics. Dietary flexibility and availability of alternative prey may become increasingly important for Arctic predators as the Arctic continues to change. [ABSTRACT FROM AUTHOR]

Predation shapes communities through consumptive and non‐consumptive effects. In the latter case, prey respond to perceived predation risk through proactive or reactive risk management strategies occurring at different spatial and temporal scales. The predator–prey space race and landscape of fear concepts are useful to better understand how predation risk affects prey behavioral decisions and distribution. We assessed predation risk effects in a terrestrial Arctic community, where the arctic fox is the main predator of ground‐nesting birds. Using high‐frequency GPS data, we estimated a predator activity landscape corresponding to fox space use patterns and validated with an artificial prey experiment that this predator activity landscape correlated with the predation risk landscape. We then investigated the effects of the fox activity landscape on multiple prey species, by assessing the anti‐predator behavior of a main prey (snow goose) actively searched for by foxes, and the nest distribution of several incidental prey species. We first found that snow geese showed a stronger level of nest defense in areas highly used by foxes, possibly responding with a reactive strategy to variation in predation risk. Then, nests of incidental prey reproducing in habitats easily accessed by foxes had a lower probability of occurrence in areas highly used by foxes, suggesting these birds may use a proactive risk management strategy by shifting their distribution away from risky areas. For incidental prey species nesting in microhabitat refuges difficult to access by foxes, probability of nest occurrence was independent of predation risk in the surrounding area, as they avoid risk at a finer spatial scale. By tracking all individuals of the dominant predator species in our study area, we demonstrated the value of using predator space use patterns to infer spatial variation in predation risk. Overall, we highlight the diversity of risk management strategies in prey sharing a common predator, hence refining our understanding of the mechanisms driving species distribution and community structure. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Background: Biologging now allows detailed recording of animal movement, thus informing behavioural ecology in ways unthinkable just a few years ago. In particular, combining GPS and accelerometry allows spatially explicit tracking of various behaviours, including predation events in large terrestrial mammalian predators. Specifically, identification of location clusters resulting from prey handling allows efficient location of killing events. For small predators with short prey handling times, however, identifying predation events through technology remains unresolved. We propose that a promising avenue emerges when specific foraging behaviours generate diagnostic acceleration patterns. One such example is the caching behaviour of the arctic fox (Vulpes lagopus), an active hunting predator strongly relying on food storage when living in proximity to bird colonies. Methods: We equipped 16 Arctic foxes from Bylot Island (Nunavut, Canada) with GPS and accelerometers, yielding 23 fox-summers of movement data. Accelerometers recorded tri-axial acceleration at 50 Hz while we obtained a sample of simultaneous video recordings of fox behaviour. Multiple supervised machine learning algorithms were tested to classify accelerometry data into 4 behaviours: motionless, running, walking and digging, the latter being associated with food caching. Finally, we assessed the spatio-temporal concordance of fox digging and greater snow goose (Anser caerulescens antlanticus) nesting, to test the ecological relevance of our behavioural classification in a well-known study system dominated by top-down trophic interactions. Results: The random forest model yielded the best behavioural classification, with accuracies for each behaviour over 96%. Overall, arctic foxes spent 49% of the time motionless, 34% running, 9% walking, and 8% digging. The probability of digging increased with goose nest density and this result held during both goose egg incubation and brooding periods. Conclusions: Accelerometry combined with GPS allowed us to track across space and time a critical foraging behaviour from a small active hunting predator, informing on spatio-temporal distribution of predation risk in an Arctic vertebrate community. Our study opens new possibilities for assessing the foraging behaviour of terrestrial predators, a key step to disentangle the subtle mechanisms structuring many predator–prey interactions and trophic networks. [ABSTRACT FROM AUTHOR]

Despite the availability of ever more data on population trends in Arctic waders, we still have limited insight into the factors influencing reproductive success and its resulting contribution to population trajectories. Here, we present data from Zackenberg in high Arctic Greenland that show no changes in timing of egg laying nor clutch size over more than two decades. With variation among species, we found earlier egg laying in seasons with earlier snowmelt, more invertebrates during the pre-laying period, earlier appearance of invertebrates and higher June temperatures. In addition, we found larger clutch sizes with earlier snowmelt, and lower clutch sizes with later nest initiation dates, together with increasing variability in clutch size during the study years in one species. Nest success was lower in late breeding seasons but seemed to increase with season progress, while nest success was much lower during the lasts 18 years of the study period than during the first part of the period. The reason for this could be both increased Arctic fox activity on the tundra and increased researcher activity at nests, which leaves olfactory clues for the foxes. Numbers of juvenile Dunlins produced seem to be negatively correlated with our index of fox activity on the tundra during nesting and fledging, whereas we found no correlations between fox activity and lemming abundance. The effects of severe events in a number of years are described, including a next to non-breeding year in 2018. Our study adds to our understanding that the Arctic is not a homogeneous biome but may show quite different regional patterns of climate change effects. [ABSTRACT FROM AUTHOR]

Indirect effects resulting from species sharing the same enemy can shape spatio‐temporal variations in species occurrence. The strength of such effects remains poorly known in natural communities composed of species from different trophic levels interacting in heterogeneous landscapes. Benefiting from a well‐known arctic vertebrate community and marked spatio‐temporal variations in the density of key prey species, we examined the effects of direct predator‐prey and indirect predator‐mediated effects on species occurrence in the landscape. We found both positive effects of one prey (lemmings), as well as negative indirect effects of another prey (colonial nesting snow geese) on the occurrence of species (ground‐nesting birds) belonging to different guilds and trophic levels but sharing a common predator (arctic fox). However, species using prey refuges available in the landscape were not or less affected by predator‐mediated effects. Similarly, the smallest (a passerine) and the largest and most dangerous species (an owl) for the shared predator were not affected by these effects. Our study provides one of the rare empirical evidence of predator‐mediated effects ascending the food web (i.e. negative indirect effect of an herbivore on avian predators) and underlines how habitat structure and species traits can modulate the strength of indirect effects in natural communities. [ABSTRACT FROM AUTHOR]

In this work, our aim is to investigate the impact of a non-Kolmogorov predator-prey-subsidy model incorporating nonlinear prey refuge and the effect of fear with Holling type II functional response. The model arises from the study of a biological system involving arctic foxes (predator), lemmings (prey), and seal carcasses (subsidy). The positivity and asymptotically uniform boundedness of the solutions of the system have been derived. Analytically, we have studied the criteria for the feasibility and stability of different equilibrium points. In addition, we have derived sufficient conditions for the existence of local bifurcations of codimension 1 (transcritical and Hopf bifurcation). It is also observed that there is some time lag between the time of perceiving predator signals through vocal cues and the reduction of prey's birth rate. So, we have analyzed the dynamical behaviour of the delayed predator-prey-subsidy model. Numerical computations have been performed using MATLAB to validate all the analytical findings. Numerically, it has been observed that the predator, prey, and subsidy can always exist at a nonzero subsidy input rate. But, at a high subsidy input rate, the prey population cannot persist and the predator population has a huge growth due to the availability of food sources. [ABSTRACT FROM AUTHOR]

Climate change has different and sometimes divergent effects on terrestrial and marine food webs, and in coastal ecosystems, these effects are tightly interlinked. Responses of opportunistic coastal predators and scavengers to climate change may thus be complex and potentially highly flexible, and can simultaneously serve as indicators of, and have profound impacts on, lower trophic levels. Gaining mechanistic understanding of these responses is therefore important, but often not feasible due to lack of long‐term data from marked individuals. Here, we used a Bayesian integrated population model (IPM) to elucidate the effects of arctic warming and concurrent changes in terrestrial and marine resource availability on population dynamics of the opportunistic arctic fox (Vulpes lagopus) in Svalbard. Joint analysis of four types of data (den survey, age‐at‐harvest, placental scars, mark‐recovery) revealed relatively stable population size and age structure over the last 22 yr (1997–2019) despite rapid environmental change linked to climate warming. This was related to the fact that terrestrial resources (reindeer carcasses, geese) became more abundant while the availability of marine resources (seal pups/carrion) decreased, and was driven by divergent trends in different vital rates (e.g., increased pregnancy rate but decreased pup survival). Balanced contributions of survival vs. reproduction and of immigration vs. local demography further stabilized population size. Our study thus sheds light on the mechanisms underlying population dynamics of opportunistic carnivores exploiting terrestrial and marine resources and suggests that exploitation of resources across different ecosystems can buffer predators against climate change. Additionally, it highlights the large potential of IPMs as tools to understand and predict the effects of environmental change on wildlife populations, even when data on marked individuals are sparse. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

As top or mesopredators, carnivores play a key role in food webs. Their survival and reproduction are usually thought to be influenced by prey availability. However, simultaneous monitoring of prey and predators is difficult, making it challenging to evaluate the impacts of prey on carnivores' demography. Using 13 years of field data on arctic foxes Vulpes lagopus in the Canadian High Arctic and a capture–recapture multi-event statistical approach, we investigated the hypothesis that increases in lemming abundance (a cyclic and unpredictable food source) and goose colony proximity (a stable but spatially and temporally limited food source) would be associated with increased apparent survival and reproduction probabilities of adults. Adult apparent survival varied greatly across years (0.13–1.00) but was neither affected by lemming nor goose variations in abundance. However, reproduction probabilities were strongly influenced by both lemming abundance and access to the goose colony. A fox breeding in the best conditions of food availability (year of high lemming density inside the goose colony) had a reproduction probability four times higher than one experiencing the worst conditions (year of low lemming density outside the goose colony). Breeding status of individuals also played a role, with breeders having a 10–20% higher probability of survival and 30% higher probability of reproduction the following year than non-breeders. As the Arctic ecosystem changes due to increased temperatures and species ranges, this study will allow better predictions of predator responses to management or environmental changes and a better understanding of ecosystem functioning. [ABSTRACT FROM AUTHOR]

Many species of seabirds and waterfowl are predominantly colonial breeders, suggesting that colonial breeding is beneficial in some way. For Arctic nesting geese, colonial breeding may be an adaptive approach to minimize the risk of nest failure through predator swamping. Yet evidence for predator swamping is inconclusive. Species in low-lying coastal zones may have to manage tradeoffs between historical (e.g., predation) and increased frequency of other threats (e.g., coastal flooding associated with storm events). As the climate continues to change, coastal obligates will be subject to rising sea levels and an increase in extreme weather events, which could exacerbate the tradeoff between flooding and predation risk. We studied the effect of nest density on nest success in the colonial nesting Black Brant (Branta bernicla nigricans) on the Tutakoke River Colony in western Alaska and explored how density effects change during years of heavy Arctic fox (Alopex lagopus) predation and coastal flooding associated with storm events. We classified the colony as containing 2 strata that differed in elevation and vegetation, and were separated by the Tutakoke River. The stratum north of the Tutakoke River was 0.25 m lower in elevation and subject to periodic tidal flooding, while the southern stratum never flooded. Nest density positively affected brant nest success in years with high levels of fox predation. Nest success was greatest at the highest density during Normal years (low levels of fox predation and no flooding; northern stratum nest success 0.81 ± 0.01, southern stratum nest success 0.81 ± 0.01) and lowest in areas of low density during Fox years (northern stratum nest success 0.38 ± 0.01, southern stratum nest success 0.31 ± 0.01). Nest success was routinely higher during Normal years at all densities compared to Flood and Fox years. Our results support the hypothesis that colonial nesting, at least in tundra habitats, may have developed as a defense mechanism to swamp mammalian predators. [ABSTRACT FROM AUTHOR]

Climate change can impact ecosystems by reshaping the dynamics of resource exploitation for predators and their prey. Alterations of these pathways could be especially intense in ecosystems characterized by a simple trophic structure and rapid warming trends, such as in the Arctic. However, quantifying the multiple direct and indirect pathways through which climate change is likely to alter trophic interactions and their relative strength remains a challenge.Here, we aim to identify direct and indirect causal mechanisms driven by climate affecting predator–prey interactions of species sharing a tundra food web.We based our study on relationships between one Arctic predator (Arctic fox) and its two main prey – lemmings (preferred prey) and snow geese (alternate prey) – which are exposed to variable local and regional climatic factors across years. We used a combination of models mapping multiple causal links among key variables derived from a long‐term dataset (21 years).We obtained several possible scenarios linking regional climate factors (Arctic oscillations) and local temperature and precipitation to the breeding of species. Our results suggest that both regional and local climate factors have direct and indirect impacts on the breeding of foxes and geese. Local climate showed a positive causal link with goose nesting success, while both regional and local climate displayed contrasted effects on the proportion of fox breeding. We found no impact of climate on lemming abundance. We observed positive relationships between lemming, fox and goose reproduction highlighting numerical and functional responses of fox to the variability of lemming abundance.Our study measures causal links and strength of interactions in a food web, quantifying both numerical response of a predator and apparent interactions between its two main prey. These results improve our understanding of the complex effects of climate on predator–prey interactions and our capacity to anticipate food web response to ongoing climate change. [ABSTRACT FROM AUTHOR]

Global warming is predicted to change ecosystem functioning and structure in Arctic ecosystems by strengthening top‐down species interactions, i.e. predation pressure on small herbivores and interference between predators. Yet, previous research is biased towards the summer season. Due to greater abiotic constraints, Arctic ecosystem characteristics might be more pronounced in winter. Here we test the hypothesis that top‐down species interactions prevail over bottom‐up effects in Scandinavian mountain tundra (Northern Sweden) where effects of climate warming have been observed and top‐down interactions are expected to strengthen. But we test this 'a priori' hypothesis in winter and throughout the 3–4 yr rodent cycle, which imposes additional pulsed resource constraints. We used snowtracking data recorded in 12 winters (2004–2015) to analyse the spatial patterns of a tundra predator guild (arctic fox Vulpes lagopus, red fox Vulpes vulpes, wolverine Gulo gulo) and small prey (ptarmigan, Lagopus spp). The a priori top‐down hypothesis was then tested through structural equation modelling, for each phase of the rodent cycle. There was weak support for this hypothesis, with top‐down effects only discerned on arctic fox (weakly, by wolverine) and ptarmigan (by arctic fox) at intermediate and high rodent availability respectively. Overall, bottom‐up constraints appeared more influential on the winter community structure. Cold specialist predators (arctic fox and wolverine) showed variable landscape associations, while the boreal predator (red fox) appeared strongly dependent on productive habitats and ptarmigan abundance. Thus, we suggest that the unpredictability of food resources determines the winter ecology of the cold specialist predators, while the boreal predator relies on resource‐rich habitats. The constraints imposed by winters and temporary resource lows should therefore counteract productivity‐driven ecosystem change and have a stabilising effect on community structure. Hence, the interplay between summer and winter conditions should determine the rate of Arctic ecosystem change in the context of global warming. [ABSTRACT FROM AUTHOR]

The endangered population of light-bellied brent geese (Branta bernicla hrota) breeding in Svalbard and north-east Greenland used to have its core breeding area in the archipelago of Tusenøyane in south-east Svalbard. Studies carried out during 1987–1991 showed that the Tusenøyane population was subject to heavy egg predation by polar bears and, in one year, Arctic foxes. Revisiting some key nesting islands in August 2018, we found few nests used by brent geese and no families. The high density of common scurvygrass (Cochlearia officinalis), a food favoured by brent geese and therefore formerly depleted by them, indicates that the geese have been absent for some time. Among other bird species, such as barnacle goose and common eider, very few young were observed as well. As potential predators, polar bears, or signs of their recent presence, were observed on most islands, and great skuas occurred on almost all islands, with 60 individuals on Lurøya, formerly an important island for geese. In contrast, only a single pair of great skuas was observed 30 years ago. The observations suggest that recent expansion of great skuas in the North Atlantic, including Svalbard, has led to a novel extreme predation pressure, additional to that caused by mammalian predators. Despite the loss of Tusenøyane as a breeding ground, the population of brent geese has increased in recent decades; so we can infer that the population now recruits from remote but mainly unknown breeding grounds. [ABSTRACT FROM AUTHOR]

In a simple, rodent-free Arctic ecosystem in Svalbard, we assessed the nest-site characteristics of the main (and highly abundant) migratory herbivore— pink-footed geese (Anser brachyrhynchus)—to determine which nesting geese were preferentially attacked and killed by the only local predator of adult geese, the Arctic fox (Vulpes lagopus). We collected data on goose carcasses and nest-site characteristics at one of the main pink-footed goose breeding areas in Svalbard. Arctic foxes depredated adult pink-footed geese from just over a quarter of the unsuccessful nests in the colony and carcasses were generally found just under 10 m away from a nest. Geese that occupied nests of poorer quality (limited visibility, further distance to forage patches and situated on flatter slopes) and were less well established (indicated by the low degree of fertilization from accumulations of goose droppings) were more likely to be depredated by Arctic foxes. As geese show a high degree of nest-site fidelity and preferentially occupy nests with better protection against depredation and closer to feeding areas, we propose that Arctic foxes targeted, and were more successful in killing younger, more inexperienced or low-quality geese that occupied less favourable nest sites. [ABSTRACT FROM AUTHOR]

Breeding geese are the preferred prey of the Arctic fox Vulpes lagopus in the high-Arctic Svalbard archipelago. According to the apparent competition hypothesis (ACH), less-abundant prey species (e.g. ptarmigan, waders and small passerines) will experience higher predation rates when breeding in association with the more common prey (geese), due to spill-over predation by the shared predator. As many of these less-abundant species are endemic and/or red-listed, increased predation can have negative repercussions on their populations. We used a one-year baited artificial nest study to assess relative nest predation risk on Svalbard Rock Ptarmigan Lagopus muta hyperborea, small waders (Purple Sandpiper Calidris maritima, Dunlin Calidris alpina, plovers Charadrius spp., and phalaropes Phalaropus spp.) and Snow bunting Plectrophenax nivalis in two study locations contrasted by nesting density of Arctic breeding geese (Pink-footed Goose Anser brachyrhynchus and Barnacle Goose Branta leucopsis). We predicted higher predation risk for the less-abundant species in the study location with higher goose abundance. However, we found that relative nest predation risk was lower in the study location with higher goose abundance, thus being compatible with apparent mutualism and/or prey swamping mechanisms. Our results contrast with those from more structurally complex Arctic ecosystems and suggest that allochtonous subsidies from temperate ecosystems structure the predation pattern in this high-Arctic tundra ecosystem. [ABSTRACT FROM AUTHOR]

Reproductive experience affects juvenile survival in a wide range of species with possible links to differences in foraging capacity and predation. Using supplementary feeding, we aimed to limit direct effect of prey abundance to investigate indirect effects of small-rodent availability and maternal experience on juvenile summer survival rates in an endangered population of arctic fox ( Vulpes lagopus (L., 1758)). We used data spanning 7 years, included a complete small-rodent cycle, comprising 49 litters and 394 cubs. The effect of small-rodent abundance on juvenile survival depended on maternal breeding experience. Cubs born by first-time-breeding females had lower survival rate when small-rodent abundance was low compared with juveniles born to experienced mothers who remained unaffected. It was unlikely due to starvation, as physical condition was unrelated to survival. Instead, we favour the explanation that intraguild predation was an important cause of mortality. There was a negative relationship between survival and amount of time cubs were left unattended, suggesting that parental behaviour affected predation. We propose that a prey switch related to small-rodent abundance caused fluctuations in intraguild predation pressure and that inexperienced females were less able to cope with predation when small rodents were scarce. [ABSTRACT FROM AUTHOR]

Identifying correctly trophic interactions is important for understanding population dynamics and ecosystem functioning. However, some predator-prey relationships may still remain undetected, due to the difficulty of observing rare predation events. We report the first observation of predation of arctic fox ( Vulpes lagopus) pups by common ravens ( Corvus corax). The predation event was witnessed on Bylot Island, Nunavut, Canada, through an automatic camera placed on a den. On June 8, 2013, the day following pup emergence from the den, the complete litter of four was killed and taken away by a pair of ravens despite the intermittent presence of the mother. This event lasted 2.5 h, occurred during a low lemming year, and resulted in the fox pair failing their reproduction. Only two other fox litters were present that summer in our 600 km study area, so this litter predated by ravens accounted for 25 % (4/16) of the pups produced. Our report shows how continuous monitoring of dens using automatic cameras can allow documentation of rare events. In addition to food competition and cache raiding, pup predation contributes to the antagonistic interactions between arctic foxes and ravens in the High Arctic, which may intensify during low lemming years. This observation allows a better understanding of species interactions within the Arctic predator guild. [ABSTRACT FROM AUTHOR]

Dynamics of avian populations may be governed by a complex Interaction between Immediate effects of predation and longer-term trophic feedbacks between Individuals and their foods. We used a long-term study of uniquely marked Black Brant geese (Branta bemicla nigricans) to estimate recruitment Into the breeding population. We related recruitment to nest success, which directly affects recruitment 2 to 3 years later. We also assessed similarly time-lagged relationships between recruitment and number of nests In the colony, a measure of local density, and pre-fledglng and first-year survival, the latter of which Is strongly Influenced by growth conditions and food availability for young of the year. We assessed relationships between number of recruits and explanatory variables In 2 sets of models, which either Included or excluded a linear trend across years In numbers of recruits. The best-performing models In each model set explained a substantial proportion of the variation In numbers of recruits 2 to 3 years later (85 and 78% In the 2 model sets, respectively). First-year survival was an Important predictor of number of recruits In both sets of models, whereas nest success was Important only In models lacking a trend across years. Number of nests In the colony had a relatively weak negative association with number of recruits. First-year survival reflects a lagged response to earlier nestpredatlon events. Reduced grazing during predation events can result In loss of grazing lawns and thus reduced growth rates of future cohorts of goslings, which are regulated by food abundance and density of broods. Our finding that recruitment Is Insufficient to maintain the breeding population results from both direct effect of predation on nests, primarily by Arctic foxes (Alopex lagopus), and longer-term Indirect effects of such predation on first-year survival of Black Brant. [ABSTRACT FROM AUTHOR]

The decline or recolonization of apex predators such as wolves and lynx, often driven by management decisions, and the expansion of smaller generalist predators such as red foxes, can have important ecosystem impacts. The mesopredator release hypothesis proposes that apex predators control medium-sized predator populations through competition and/or intraguild predation. The decline of apex predators thus leads to an increase in mesopredators, possibly with a negative impact on prey populations. Information about the abundance of mammalian tundra predators, wolf ( Canis lupus), wolverine ( Gulo gulo), lynx ( Lynx lynx), red fox ( Vulpes vulpes) and arctic fox ( Vulpes lagopus) was collected from local active outdoors people during semi-structured interviews in 14 low arctic or sub-arctic settlements in western Eurasia. The perceived abundance of red fox decreased with higher wolf abundance and in more arctic areas, but the negative effect of wolves decreased in more arctic and therefore less productive ecosystems. The perceived abundance of arctic fox increased towards the arctic and in areas with colder winters. Although there was a negative correlation between the two fox species, red fox was not included in the model for perceived arctic fox abundance, which received most support. Our results support the mesopredator release hypothesis regarding the expansion of red foxes in subarctic areas and indicate that top-down control by apex predators is weaker in less productive and more arctic ecosystems. We showed that local ecological knowledge is a valuable source of information about large-scale processes, which are difficult to study through direct biological investigations. [ABSTRACT FROM AUTHOR]

Pink-footed geese Anser brachyrhynchus nest in two contrasting but commonly found habitats: steep cliffs and open tundra slopes. In Svalbard, we compared nest densities and nesting success in these two environments over ten breeding seasons to assess the impact of spring snow cover, food availability to nesting adults and arctic fox Vulpes lagopus (main terrestrial predator) abundance. In years with extensive spring snow cover, fewer geese at both colonies attempted to breed, possibly because snow cover limited pre-nesting feeding opportunities, leaving adults in poor breeding condition. Nesting success at the steep cliff colony was lower with extensive spring snow cover; such conditions force birds to commit to repeated and prolonged recess periods at far distant feeding areas, leaving nests open to predation. By contrast, nesting success at the open tundra slope was not affected by spring snow cover; even if birds were apparently in poor condition they could feed immediately adjacent to their nests and defend them from predators. Foxes were the main nest predator in the open tundra slopes but avian predators likely had a larger impact at the steep cliffs colony. Thus, the relative inaccessibility of the cliffs habitat may bring protection from foxes but also deprives geese from readily accessing feeding areas, with the best prospects for successful nesting in low spring snow cover years. Our findings indicate that spring snow cover, predator abundance and food proximity did not uniformly influence nesting success of this herbivore, and their effects were dependent on nesting habitat choice. [ABSTRACT FROM AUTHOR]

The arctic fox (Vulpes lagopus) is endemic to the Arctic where it holds a central position in the trophic interactions. The diet of the species has previously been described as being highly flexible, but whether this flexibility is a constant trait through time, or merely reflects fast temporal changes in abundance among prey taxa, has so far been poorly resolved. Using molecular analyses of arctic fox scats from Northeast Greenland, we first examined the temporal dynamics of arctic fox diets during the short snow-free season, and then examined whether local food availability at different sites affected arctic fox dependence on lemmings. Arctic fox diets included most terrestrial vertebrate species found in the region, and exhibited substantial temporal changes, generally reflecting the dynamic changes in prey availability from late winter through autumn. This dietary flexibility was also reflected geographically, with arctic foxes consuming a variety of local prey (mainly waterfowl and lemmings) in summer. Moreover, the dietary response of arctic foxes to changes in lemming abundance depended on access to non-lemming prey. Based on these findings, we discuss whether varying degrees of lemming-dependency, combined with geographical differences in winter food availability, may explain previously published differences in arctic fox breeding patterns in high arctic Greenland. [ABSTRACT FROM AUTHOR]

In the Arctic tundra, snow is believed to protect lemmings from mammalian predators during winter. We hypothesized that snow quality (depth and hardness) should affect mammalian predation rates on lemmings, but that this effect would depend on the predator hunting strategy; and that predation by ermines (Mustela erminea), which can hunt lemmings under the snow, should be higher in preferred lemming habitats. We measured snow depth and hardness at tunnels made by arctic fox (Vulpes lagopus) predation attempts, at winter nests nonpredated and predated by ermines, and at random locations. We also determined winter nest density in 3 habitats (wet, mesic, and gully). Deep and hard snow restricted fox predation attempts made by jumping through the snow, but not those made by digging. Ermine predation was unaffected by snow depth and weakly by nest density but was higher in gully and intermediate in mesic habitats, which are conducive to high snow accumulation, compared to the wet habitat. These results indicate that habitat-related topographical features are more important than snow depth or nest density per se in affecting the winter foraging strategy of ermines. Overall, even though we found a relatively weak effect of the snow cover on predation by foxes and ermines, it is difficult to predict how upcoming changes to the snow cover will affect lemming vulnerability to mammalian predators because a wide range of snow conditions may result from climate warming. [ABSTRACT FROM AUTHOR]

Perturbations to ecosystems have the potential to directly and indirectly affect species interactions, with subsequent impacts on population dynamics and the vital rates that regulate them., The few long-term studies of common eider breeding ecology indicate that reproductive success is low in most years, interrupted by occasional boom years. However, no study has explicitly examined the drivers of long-term variation in reproductive success., Here, we use encounter history data collected across 41 years to examine the effects of arctic foxes (a terrestrial nest predator), local abundance and spatial distribution of lesser snow geese (an alternative prey source), and spring climate on common eider nest success., Eider nest success declined over the course of the study, but was also highly variable across years. Our results supported the hypothesis that the long-term decline in eider nest success was caused by apparent competition with lesser snow geese, mediated by shared predators. This effect persisted even following a large-scale exodus of nesting geese from the eider colony. Nest success was also lowest in years of low arctic fox index, presumably driven by prey switching in years of low small mammal availability. However, increased snow goose abundance appeared to buffer this effect through prey swamping. The effect of spring climate depended on the stage of the breeding season; cold and wet and warm and dry conditions in early spring were correlated with decreased nest success, whereas warm and wet conditions in late spring increased eider nest success., These results underscore the significance of both trophic interactions and climate in regulating highly variable vital rates, which likely have important consequences for population dynamics and the conservation of long-lived iteroparous species. [ABSTRACT FROM AUTHOR]

Abstract: Ecosystems alterations can profoundly affect species occurrence and distribution, thereby influencing trophic and/or competitive interactions. Arctic foxes have been fully protected in Fennoscandia following their drastic decline in the early 19th century, and their lack of recovery has been hypothesized to result from increased interspecific competition with red foxes that have colonized the arctic fox’s range and/or changes in prey dynamics due to increased variation in climatic conditions. We used a large-scale spatio-temporal study combined with an extensive red fox removal intervention to test these two hypotheses by evaluating the relative importance of diverse environmental factors affecting the recolonization of arctic foxes in Northern Norway. Arctic foxes were never observed at sites where just a few daily observations of red foxes were recorded, and the probability of recolonization was zero at sites where no red fox was removed. The probability of recolonization increased when lemming abundance was very high, but the relative importance of this variable was half that of red foxes. Thus, our results lend support to both hypotheses, but they clearly highlight the presence of red foxes as the factor most limiting arctic fox recolonization in this part of its distribution. As the abundance of arctic foxes has remained extremely low even after more than 70years of full protection, direct conservation actions seem to be needed to promote the recovery of arctic fox populations. Our research therefore highlights that conservation actions targeting a major reduction in red fox numbers are needed because the competitive interaction with red foxes is the most important factor limiting recolonization of this species. [Copyright &y& Elsevier]

Numbers of Western Atlantic Red Knots ( Calidris canutus rufa (A. Wilson, 1813)) have declined since 1980, with a sustained downward trend observed after 1998. Because the reproductive output of a closely related Eurasian subspecies ( Calidris canutus islandica (L., 1767)) is known to be low when lemming numbers are low, and because lemming cycles in Fennoscandia were recently interrupted, we investigated the relationship between the rodent cycle in arctic Canada and numbers of C. c. rufa migrating through the United States. Shooting records from Cape Cod in the 1800s and Red Knot counts on the Delaware Bay from 1986 to 1998 cycled with 4-year periods. Annual peaks in numbers of Red Knots stopping in the Delaware Bay in 1986-1998 occurred 2 years after arctic rodent peaks more often than expected at random. The results suggest that the reproductive output of C. c. rufa was linked to the rodent cycle before the Red Knot decline. There is no evidence that such a link existed after 1998. These findings are consistent with the hypothesis that an interruption of the rodent cycle in Red Knot habitat could have been a driver in the recent Red Knot decline. Field studies in the Arctic are needed to further investigate this hypothesis. [ABSTRACT FROM AUTHOR]