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Context: In a conservation context, identifying key habitats suitable for reproduction, foraging, or survival is a useful tool, yet challenging for species with large geographic distributions and/or living in remote regions. Objectives: The objective of this study is to identify selected habitats at multiple levels and scales of the threatened eastern North American population of golden eagles (Aquila chrysaetos). We studied habitat selection at three levels: landscape (second order of selection), foraging (third order of selection), and nesting (fourth order of selection). Methods: Using tracking data from 30 adults and 366 nest coordinates spanning over a 1.5 million km2 area in remote boreal and Arctic regions, we modelled the three levels of habitat selection with resource selection functions using seven environmental features (aerial, topographical, and land cover). We then calculated the relative probability of selection in the study area to identify regions with higher probabilities of selection. Results: Eagles selected more for terrain ruggedness index and relative elevation than land cover (i.e., forest cover, distance to water; mean difference in relative selection strength: 1.2 [0.71; 1.69], 95% CI) at all three levels. We also found that the relative probability of selection at all three levels was ~ 25% higher in the Arctic than in the boreal regions. Eagles breeding in the Arctic travelled shorter foraging distances with greater access to habitat with a high probability of selection than boreal eagles. Conclusion: Here we found which aerial and topographical features were important for several of the eagles' life cycle needs. We also identified important areas to monitor and preserve this threatened population. The next step is to quantify the quality of habitat by linking our multi-level, multi-scale approach to population demography and performance such as reproductive success. [ABSTRACT FROM AUTHOR]

Mercury (Hg) pollution remains a concern to Arctic ecosystems, due to long-range transport from southern industrial regions and melting permafrost and glaciers. The objective of this study was to identify intrinsic, extrinsic, and temporal factors influencing Hg concentrations in Arctic-breeding shorebirds and highlight regions and species at greatest risk of Hg exposure. We analyzed 1094 blood and 1384 feather samples from 12 shorebird species breeding at nine sites across the North American Arctic during 2012 and 2013. Blood Hg concentrations, which reflect Hg exposure in the local area in individual shorebirds: 1) ranged from 0.01–3.52 μg/g ww, with an overall mean of 0.30 ± 0.27 μg/g ww; 2) were influenced by species and study site, but not sampling year, with birds sampled near Utqiaġvik, AK, having the highest concentrations; and 3) were influenced by foraging habitat at some sites. Feather Hg concentrations, which reflected Hg exposure from the wintering grounds: 1) ranged from 0.07–12.14 μg/g fw in individuals, with an overall mean of 1.14 ± 1.18 μg/g fw; and 2) were influenced by species and year. Most Arctic-breeding shorebirds had blood and feather Hg concentrations at levels where no adverse effects of exposure were predicted, though some individuals sampled near Utqiaġvik had Hg levels that would be considered of concern. Overall, these data increase our understanding of how Hg is distributed in the various shorebird breeding areas of the Arctic, what factors predispose Arctic-breeding shorebirds to Hg exposure, and lay the foundation for future monitoring efforts. [ABSTRACT FROM AUTHOR]

Empirical observations and mathematical models show that climate warming can lead to the northern (or, more generally, poleward) spread of host species ranges and their corresponding diseases. Here, we consider an unexpected possibility whereby climate warming facilitates disease spread in the opposite direction to the directional shift in the host species range. To explore this possibility, we consider two host species, both susceptible to a disease, but spatially isolated due to distinct thermal niches, and where prior to climate warming the disease is endemic in the northern species only. Previous theoretical results show that species distributions can lag behind species thermal niches when climate warming occurs. As such, we hypothesize that climate warming may increase the overlap between northern and southern host species ranges, due to the northern species lagging behind its thermal tolerance limit. To test our hypothesis, we simulate climate warming as a reaction-diffusion equation model with a Susceptible-Infected (SI) epidemiological structure, for two competing species with distinct temperature-dependent niches. We show that climate warming, by shifting both species niches northwards, can facilitate the southward spread of disease, due to increased range overlap between the two populations. As our model is general, our findings may apply to viral, bacterial, and prion diseases that do not have thermal tolerance limits and are inextricably linked to their hosts distributions, such as the spread of rabies from arctic to red foxes. [ABSTRACT FROM AUTHOR]

Population-genomic studies can shed new light on the effect of past demographic processes on contemporary population structure. We reassessed phylogeographical patterns of a classic model species of postglacial recolonisation, the brown bear (Ursus arctos), using a range-wide resequencing dataset of 128 nuclear genomes. In sharp contrast to the erratic geographical distribution of mtDNA and Y-chromosomal haplotypes, autosomal and X-chromosomal multi-locus datasets indicate that brown bear population structure is largely explained by recent population connectivity. Multispecies coalescent based analyses reveal cases where mtDNA haplotype sharing between distant populations, such as between Iberian and southern Scandinavian bears, likely results from incomplete lineage sorting, not from ancestral population structure (i.e., postglacial recolonisation). However, we also argue, using forward-in-time simulations, that gene flow and recombination can rapidly erase genomic evidence of former population structure (such as an ancestral population in Beringia), while this signal is retained by Y-chromosomal and mtDNA, albeit likely distorted. We further suggest that if gene flow is male-mediated, the information loss proceeds faster in autosomes than in X chromosomes. Our findings emphasise that contemporary autosomal genetic structure may reflect recent population dynamics rather than postglacial recolonisation routes, which could contribute to mtDNA and Y-chromosomal discordances. The genetic structure of modern-day brown bears mainly reflects contemporary population connectivity. Recent gene flow barriers have obscured the genomic signatures of postglacial recolonisation. [ABSTRACT FROM AUTHOR]

Tumors initiate by mutations in cancer cells, and progress through interactions of the cancer cells with non-malignant cells of the tumor microenvironment. Major players in the tumor microenvironment are cancer-associated fibroblasts (CAFs), which support tumor malignancy, and comprise up to 90% of the tumor mass in pancreatic cancer. CAFs are transcriptionally rewired by cancer cells. Whether this rewiring is differentially affected by different mutations in cancer cells is largely unknown. Here we address this question by dissecting the stromal landscape of BRCA-mutated and BRCA Wild-type pancreatic ductal adenocarcinoma. We comprehensively analyze pancreatic cancer samples from 42 patients, revealing different CAF subtype compositions in germline BRCA-mutated vs. BRCA Wild-type tumors. In particular, we detect an increase in a subset of immune-regulatory clusterin-positive CAFs in BRCA-mutated tumors. Using cancer organoids and mouse models we show that this process is mediated through activation of heat-shock factor 1, the transcriptional regulator of clusterin. Our findings unravel a dimension of stromal heterogeneity influenced by germline mutations in cancer cells, with direct implications for clinical research. Cancer-associated fibroblasts are transcriptionally rewired by signals from the cancer cells, resulting in heterogeneous populations. Here the authors show that loss of BRCA function in pancreatic cancer cells leads to HSF1–dependent accumulation of immune-regulatory clusterin-positive cancer associated fibroblasts. [ABSTRACT FROM AUTHOR]

Although p53 inactivation promotes genomic instability1 and presents a route to malignancy for more than half of all human cancers2,3, the patterns through which heterogenous TP53 (encoding human p53) mutant genomes emerge and influence tumorigenesis remain poorly understood. Here, in a mouse model of pancreatic ductal adenocarcinoma that reports sporadic p53 loss of heterozygosity before cancer onset, we find that malignant properties enabled by p53 inactivation are acquired through a predictable pattern of genome evolution. Single-cell sequencing and in situ genotyping of cells from the point of p53 inactivation through progression to frank cancer reveal that this deterministic behaviour involves four sequential phases—Trp53 (encoding mouse p53) loss of heterozygosity, accumulation of deletions, genome doubling, and the emergence of gains and amplifications—each associated with specific histological stages across the premalignant and malignant spectrum. Despite rampant heterogeneity, the deletion events that follow p53 inactivation target functionally relevant pathways that can shape genomic evolution and remain fixed as homogenous events in diverse malignant populations. Thus, loss of p53—the ‘guardian of the genome’—is not merely a gateway to genetic chaos but, rather, can enable deterministic patterns of genome evolution that may point to new strategies for the treatment of TP53-mutant tumours.Malignant evolution enabled by p53 inactivation in mice proceeds through an ordered and predictable pattern of Trp53 loss of heterozygosity, accumulation of deletions, genome doubling and the emergence of gains and amplifications. [ABSTRACT FROM AUTHOR]

The current and rapid anthropogenic environmental changes could disproportionately impact ecosystems, particularly when they affect species with critical roles in ecosystem integrity. As top predators, raptors provide critical top-down ecosystem services and structure food webs. Yet, many avian predators are currently experiencing global population declines and some are threatened with extinction. The dire conservation status of numerous raptor species warrants urgent action, and detailed ecological data are needed to guide management strategy, including empirical knowledge regarding genetic structure. To that end, we compiled published studies investigating population genetic structure in raptors. Out of a total of 83 publications on 50 raptors species published, we identified a lack of empirical genetic studies for species from the Southern Hemisphere and species with a high level of extinction risk according to IUCN Red List criteria. Only 24% of the species studied are considered "threatened" (i.e., with the "Vulnerable", "Endangered", or "Critically Endangered" status). We found a significant signal of genetic differentiation in 41 species (82%) at the study-specific population. Isolation-by-Distance is a common pattern of genetic differentiation in raptors. Future steps in raptor conservation could prioritize facilitating genetic studies on species located in the Southern Hemisphere and on species with a conservation status. A better inclusion of some key genetic metrics (e.g., Ne, Ne/Nc, genetic diversity) in published studies will further help management and conservation across various species and ecosystems. [ABSTRACT FROM AUTHOR]

An expected consequence of climate warming is an expansion of the geographical distribution of biting insects and associated arthropod-borne viruses (arboviruses). Emerging and re-emerging arboviruses that can affect human and animal health are likely to pose significant consequences for Northern communities where access to health resources is limited. In the North American Arctic, little is known about arboviruses. Thus, in 2019, we sampled biting insects in Nunavik, Northern Québec (Kuujjuaq), Nunavut (Igloolik, Karrak Lake and Cambridge Bay), Northwest Territories (Igloolik and Yellowknife) and Alaska (Fairbanks). The main objective was to detect the presence of California serogroup (CSG) viruses– a widespread group of arboviruses across North America and that are known to cause a wide range of symptoms, ranging from mild febrile illness to fatal encephalitis. Biting insects were captured twice daily for a 7-day period in mid-summer, using a standardised protocol consisting of 100 figure-eight movements of a sweep net. Captured specimens were separated by genus (mosquitoes) or by superfamily (other insects) and then grouped into pools of 75 by geographical locations. In total, 5079 Aedes mosquitoes and 1014 Simulioidae flies were caught. We report the detection of CSG viruses RNA in mosquitoes captured in Nunavut (Karrak Lake) and Nunavik (Kuujjuaq). We also report, for the first time in North America, the presence of CSG viruses RNA in Simulioidae flies. These results highlight the use of biting insects for tracking any future emergence of arboviruses in the North, thereby providing key information for public health in Northern communities. [ABSTRACT FROM AUTHOR]

Most small rodent populations in the world have fascinating population dynamics. In the northern hemisphere, voles and lemmings tend to show population cycles with regular fluctuations in numbers. In the southern hemisphere, small rodents tend to have large amplitude outbreaks with less regular intervals. In the light of vast research and debate over almost a century, we here discuss the driving forces of these different rodent population dynamics. We highlight ten questions directly related to the various characteristics of relevant populations and ecosystems that still need to be answered. This overview is not intended as a complete list of questions but rather focuses on the most important issues that are essential for understanding the generality of small rodent population dynamics. [ABSTRACT FROM AUTHOR]

Migratory species display a range of migration patterns between irruptive (facultative) to regular (obligate), as a response to different predictability of resources. In the Arctic, snow directly influences resource availability. The causes and consequences of different migration patterns of migratory species as a response to the snow conditions remains however unexplored. Birds migrating to the Arctic are expected to follow the spring snowmelt to optimise their arrival time and select for snow-free areas to maximise prey encounter en-route. Based on large-scale movement data, we compared the migration patterns of three top predator species of the tundra in relation to the spatio-temporal dynamics of snow cover. The snowy owl, an irruptive migrant, the rough-legged buzzard, with an intermediary migration pattern, and the peregrine falcon as a regular migrant, all followed, as expected, the spring snowmelt during their migrations. However, the owl stayed ahead, the buzzard stayed on, and the falcon stayed behind the spatio-temporal peak in snowmelt. Although none of the species avoided snow-covered areas, they presumably used snow presence as a cue to time their arrival at their breeding grounds. We show the importance of environmental cues for species with different migration patterns. [ABSTRACT FROM AUTHOR]

Glaciers should be prioritized in conservation agendas — and soon. Analysis suggests that glaciers could lose around half their area by the century’s end, with uncertain consequences for postglacial ecosystems.Predicted loss of glacier area and its ecological impact. [ABSTRACT FROM AUTHOR]

Food hoarding is often considered an adaptive behaviour to extend the period of availability of food resources. Finding the right caching site for storage and retrieval is of paramount importance, yet how caching sites are selected is poorly known. Here, we examine site selection for egg caching by a tundra predator, the arctic fox, Vulpes lagopus, which can overcome large seasonal prey variations by extensive caching. During the short arctic summer, colonial breeding birds like geese produce in a short time period many eggs, which provide a large quantity of predictable resources for consumption and caching. We predicted that foxes would select caching sites with specific characteristics, such as shallow permafrost, and tall hummocks (small mounds in tundra landscapes, which should facilitate caching and provide visual cues for subsequent retrieval). We sampled the main physical characteristics of 48 caches and paired random sites inside a Greater Snow Goose (Chen caerulescens) colony. Our study shows that foxes favour cache sites characterized by hummocks nearly twice as higher than at nearby random sites. The depth of the active layer of permafrost did not influence cache site selection. Foxes may select tundra features that possibly enhance caching efficiency and retrieval probability. Our study elucidates one aspect of food hoarding behaviour in extreme habitats characterized by strong variations of resource availability. [ABSTRACT FROM AUTHOR]

Arctic environments have relatively simple ecosystems. Yet, we still lack knowledge of the spatio-temporal dynamics of many Arctic organisms and how they are affected by local and regional processes. The Arctic hare ( Lepus arcticus) is a large lagomorph endemic to high Arctic environments in Canada and Greenland. Current knowledge about this herbivore is scarce and the temporal and spatial dynamics of their populations are poorly understood. Here, we present observations on Arctic hares in two sites on north Greenland (Hall and Washington lands) and one adjacent site on Ellesmere Island (Judge Daly Promontory). We recorded a large range of group sizes from 1 to 135 individuals, as well as a substantial variation in hare densities among the three sites (Hall land: 0 animals/100 km, Washington land 14.5-186.7 animals/100 km, Judge Daly Promontory 0.18-2.95 animals/100 km). However, pellet counts suggested that both Hall land and Judge Daly Promontory hosted larger populations at other times. We suggest that our results could have been caused by three spatially differentiated populations with asynchronous population fluctuations. With food limitation being a likely driver behind the observed variation, we argue that food limitation likely interacts with predation and competition in shaping the spatial dynamics of Arctic hares in this region. [ABSTRACT FROM AUTHOR]

Global climate change induces species range shifts and population expansion to higher latitudes in response to rising temperatures. One consequence of climate-induced range shifts is an increased sympatry between related but previously isolated species, potentially resulting in interspecific interactions and hybridization. The Arctic is more rapidly affected by climate warming than any region on Earth and resident species may be prone to interspecific hybridization due to the immigration of new colonizing species. The red fox Vulpes vulpes expanded its range into the Arctic during the twentieth century and is now in sympatry with the native Arctic fox Vulpes lagopus in many places. In this context, an Arctic-like fox displaying an unusual reddish winter coat was observed in 2013 in Nunavut, Canada, a phenotype unknown by Inuit people to date. In this study, we assessed the biological origin of this specimen with a multigenic approach using markers located on mitochondrial DNA, sex (X and Y) chromosomes, and autosomes (microsatellites and the melanocortin 1 receptor (MC1R) gene; a gene involved in the color polymorphism in canids). Our comparative analyses with genetic material from Arctic and red foxes displaying 'classic' phenotypes ( N = 14 and 16, respectively) suggested a pure Arctic fox origin of the specimen. Specifically, this fox yielded mtDNA, X-linked, Y-linked, and MC1R alleles specific to Arctic fox. Bayesian genetic assignment based on 16 microsatellite loci assigned it to Arctic fox with high confidence ( q = 99.7%). Thus, a recent hybrid origin for this specimen is excluded. This alternative winter coat color polymorphism in Arctic fox requires further analyses to determine its underlying genetic mechanism. [ABSTRACT FROM AUTHOR]

Assessing the scale of ecological changes that have occurred since the onset of the Anthropocene is challenging. One major problem is that of shifting baselines, whereby the norms we set for judging the state of species, populations, or ecosystems change over time due to incomplete information. Here we show how data mining can be used to fill some of the information gaps fueling shifting baselines. We used as example an elusive species, the wolverine ( Gulo gulo), given that information gaps are so prevailing for such species. We applied the concept of data mining to search documents hosted on publicly accessible online repositories and found information about the historical occurrence of wolverines that allowed us to revise their historical range in eastern North America. We found 12 historical accounts attesting the presence of wolverines in various parts of the Maritime Provinces of Canada, of which 11 were new to contemporary science. According to our results, the eastern limit of the historical range of the wolverine should be extended to include the current jurisdictions of New Brunswick and Nova Scotia. Biological change is the central paradigm of species status assessments. We show that online repositories of public domain literature can now be critical sources of information to assess biological change, including in the case of elusive species. Data mining constitutes a productive tool to uncover useful knowledge hidden in a sea of digitized historical information, and should thus allow researchers and conservationists to more effectively mitigate the problem of shifting baselines. [ABSTRACT FROM AUTHOR]

Understanding how climate change and increasing human impacts may exert pressure on ecosystems and threaten biodiversity requires efficient monitoring programs. Indicator species have been proposed as useful tools, and predators and their diet may be particularly suitable. The vast and remote arctic tundra represents a good case study as shifts in ecosystem states are presently occurring, and monitoring is a major challenge. Here we assess what stable isotopes reflecting the diet of the arctic fox, a widespread and highly flexible top predator, can contribute to effective monitoring of the vertebrate prey basis of Arctic tundra. We used data collected over 2-5 years from six sites in the Eurasian Arctic and Greenland. Stable isotope signatures of arctic fox winter fur reflected both spatial and temporal variability in the composition of the vertebrate prey basis. Clear contrasts were apparent in the importance of marine resources, as well as of small rodents and their multiannual density fluctuations. Some important resources could however not be separated because of confounding isotopic signatures. Moreover, except for preferred prey, the proportions of prey in the diet may not necessarily reflect the relative importance of species in the community of available prey. Knowing these limitations, we suggest that the arctic fox diet as inferred from stable isotopes could serve as one of several key targets in ecosystem-based monitoring programs. [ABSTRACT FROM AUTHOR]

Many different ecological factors affecting the size, use, and spatial configuration of home ranges have been investigated, yet the chronology of the breeding cycle has been relatively under studied. Here, we studied peregrine falcons ( Falco peregrinus) to describe variation in home range within and between breeding seasons in the Yamal peninsula, a region of the Russian Arctic with a high breeding density of peregrines. We used satellite telemetry to investigate variation in home range at different stages of the breeding cycle during three breeding seasons (2009-2011). We fitted Argos satellite transmitters to 10 breeding peregrines (nine females and one male) and two male fledglings. All breeding females showed fidelity to the region of the southwestern Yamal peninsula, but they were not necessarily faithful to their specific breeding ranges with 33 % dispersing to new ranges up to 40 km away. The population of peregrines in our study area was relatively synchronous in their breeding chronology, with clutches initiated in close synchrony in early June despite the birds arriving on their breeding ranges ca. 3 weeks earlier. The average home range size for breeding females was 98 km (95 % Maximum Convex Polygon). Over the breeding season, the home range area utilized by females increased in the late nestling period and again after the chicks fledged. Expansion of the home range coincided with changes in behavior associated with parental care, resulting in greater activity and more time spent away from the nest area when the female began hunting to provision nestlings and fledglings. [ABSTRACT FROM AUTHOR]

The rough-legged buzzard, a circumpolar avian predator, is usually defined as rodent specialist in the tundra but as a generalist in the boreal zone, leaving open the question of where the shift in feeding strategy occurs. Here, we investigated the diet and breeding biology of buzzards as well as abundance of their possible prey during 5 years in the low-Arctic shrub tundra on the Nenetsky Ridge, Russia. We employed three complementary methods to assess the diet of this Arctic predator-pellet dissection, identification of prey remains on nests, and stable isotope analysis-to overcome their respective limitations. We documented fluctuations in abundances of the likely prey, namely rodents, ptarmigans, and hares. Nesting density of buzzards changed substantially over the years, but did not track the abundance cycle of the rodents. The number of buzzard fledglings was relatively low (1.08 ± 0.3) and did not change according to the density of rodents. In the year when rodents were at their lowest abundance, diet analyses of nestlings documented a shift from rodents to alternative prey, with a decrease in the proportion of tundra voles and an increase in proportion of hares, ptarmigans, and ducks. Here, we argue that buzzards may adopt different feeding strategies along the gradient from generalists to specialists. While the rough-legged buzzard is usually considered a small rodent specialist, our study shows that it can shift to alternative prey where or when rodents are scarce and when alternative prey are sufficiently abundant to provide subsistence for breeding. [ABSTRACT FROM AUTHOR]

Climate-driven range fluctuations during the Pleistocene have continuously reshaped species distribution leading to populations of contrasting genetic diversity. Contemporary climate change is similarly influencing species distribution and population structure, with important consequences for patterns of genetic diversity and species' evolutionary potential. Yet few studies assess the impacts of global climatic changes on intraspecific genetic variation. Here, combining analyses of molecular data with time series of predicted species distributions and a model of diffusion through time over the past 21 kyr, we unravel caribou response to past and future climate changes across its entire Holarctic distribution. We found that genetic diversity is geographically structured with two main caribou lineages, one originating from and confined to Northeastern America, the other originating from Euro-Beringia but also currently distributed in western North America. Regions that remained climatically stable over the past 21 kyr maintained a high genetic diversity and are also predicted to experience higher climatic stability under future climate change scenarios. Our interdisciplinary approach, combining genetic data and spatial analyses of climatic stability (applicable to virtually any taxon), represents a significant advance in inferring how climate shapes genetic diversity and impacts genetic structure. [ABSTRACT FROM AUTHOR]

In patchy habitats, the relationship between animal abundance and cover of a preferred habitat may change with the availability of that habitat, resulting in a functional response in habitat use. Here, we investigate the relationship of two specialized herbivores, willow ptarmigan ( Lagopus lagopus) and mountain hare ( Lepus timidus), to willows ( Salix spp.) in three regions of the shrub tundra zone-northern Norway, northern European Russia and western Siberia. Shrub tundra is a naturally patchy habitat where willow thickets represent a major structural element and are important for herbivores both as food and shelter. Habitat use was quantified using feces counts in a hierarchical spatial design and related to several measures of willow thicket configuration. We document a functional response in the use of willow thickets by ptarmigan, but not by hares. For hares, whose range extends into forested regions, occurrence increased overall with willow cover. The occurrence of willow ptarmigan showed a strong positive relationship to willow cover and a negative relationship to thicket fragmentation in the region with lowest willow cover at landscape scale, where willow growth may be limited by reindeer browsing. In regions with higher cover, in contrast, such relationships were not observed. Differences in predator communities among the regions may contribute to the observed pattern, enhancing the need for cover where willow thickets are scarce. Such region-specific relationships reflecting regional characteristics of the ecosystem highlight the importance of large-scale investigations to understand the relationships of habitat availability and use, which is a critical issue considering that habitat availability changes quickly with climate change and human impact. [ABSTRACT FROM AUTHOR]

Despite numerous studies on breeding dispersal, it is still unclear how habitat heterogeneity and previous nesting success interact to determine nest-site fidelity at various spatial scales. In this context, we investigated factors affecting breeding dispersal in greater snow geese ( Anser caerulescens atlanticus), an Arctic breeding species nesting in two contrasting habitats (wetlands and mesic tundra) with variable pattern of snowmelt at the time of settlement in spring. From 1994 to 2005, we monitored the nesting success and breeding dispersal of individually marked females. We found that snow geese showed a moderate amount of nest-site fidelity and considerable individual variability in dispersal distance over consecutive nesting attempts. This variability can be partly accounted for by the annual timing of snowmelt. Despite this environmental constraint, habitat differences at the colony level consistently affected nesting success and settlement patterns. Females nesting in wetlands had higher nesting success than those nesting in mesic tundra. Moreover, geese responded adaptively to spatial heterogeneity by showing fidelity to their nesting habitat, independently of snowmelt pattern. From year to year, geese were more likely to move from mesic to high-quality wetland habitat, regardless of previous nesting success and without cost on their subsequent nesting performance. The unpredictability of snowmelt and the low cost of changing site apparently favour breeding-site dispersal although habitat quality promotes fidelity at the scale of habitat patches. [ABSTRACT FROM AUTHOR]

Cache recovery is critical for evolution of hoarding behaviour, because the energy invested in caching may be lost if consumers other than the hoarders benefit from the cached food. By raiding food caches, animals may exploit the caching habits of others, that should respond by actively defending their caches. The arctic fox ( Alopex lagopus) is the main predator of lemmings and goose eggs in the Canadian High Arctic and stores much of its prey in the ground. Common ravens ( Corvus corax) are not as successful as foxes in taking eggs from goose nests. This generalist avian predator regularly uses innovation and opportunism to survive in many environments. Here, we provide the first report that ravens can successfully raid food cached by foxes, and that foxes may defend their caches from ravens. [ABSTRACT FROM AUTHOR]

The objective of this study was to characterize the effects of soil burn severity and initial tree composition on long-term forest floor dynamics and ecosystem biomass partitioning within the Picea mariana [Mill.] BSP-feathermoss bioclimatic domain of northwestern Quebec. Changes in forest floor organic matter and ecosystem biomass partitioning were evaluated along a 2,355-year chronosequence of extant stands. Dendroecological and paleoecological methods were used to determine the time since the last fire, the soil burn severity of the last fire (high vs. low severity), and the post-fire tree composition of each stand ( P. mariana vs. Pinus banksiana Lamb). In this paper, soil burn severity refers to the thickness of the organic matter layer accumulated above the mineral soil that was not burned by the last fire. In stands originating from high severity fires, the post-fire dominance by Pinus banksiana or P. mariana had little effect on the change in forest floor thickness and tree biomass. In contrast, stands established after low severity fires accumulated during the first century after fire 73% thicker forest floors and produced 50% less tree biomass than stands established after high severity fires. Standing tree biomass increased until approximately 100 years after high severity fires, and then decreased at a logarithmic rate in the millennial absence of fire. Forest floor thickness also showed a rapid initial accumulation rate, and continued to increase in the millennial absence of fire at a much slower rate. However, because forest floor density increased through time, the overall rate of increase in forest floor biomass (58 g m−2 y−1) remained constant for numerous centuries after fire (700 years). Although young stands (< 200 years) have more than 60% of ecosystem biomass locked-up in living biomass, older stands (> 200 years) sequester the majority (> 80%) of it in their forest floor. The results from this study illustrate that, under similar edaphic conditions, a single gradient related to time since disturbance is insufficient to account for the full spectrum of ecosystem biomass dynamics occurring in eastern boreal forests and highlights the importance of considering soil burn severity. Although fire severity induces diverging ecosystem biomass dynamics in the short term, the extended absence of fire brings about a convergence in terms of ecosystem biomass accumulation and partitioning. [ABSTRACT FROM AUTHOR]

Authors would like to correct error in affiliation in the original publication of the article. [ABSTRACT FROM AUTHOR]

An amendment to this paper has been published and can be accessed via a link at the top of the paper. [ABSTRACT FROM AUTHOR]