2018: Arctic researchers have just witnessed another extreme summer-but in a new sense of the word. Although public interest has long been focused on general warming trends and trends towards a lower ...sea ice cover in the Arctic Ocean, this summer saw the realization of another predicted trend: that of increasing precipitation during the winter months and of increased year-to-year variability. In a well-studied ecosystem in Northeast Greenland, this resulted in the most complete reproductive failure encountered in the terrestrial ecosystem during more than two decades of monitoring: only a few animals and plants were able to reproduce because of abundant and late melting snow. These observations, we suggest, should open our eyes to potentially drastic consequences of predicted changes in both the mean and the variability of arctic climate.
We discuss the notorious problem of order selection in hidden Markov models, that is of selecting an adequate number of states, highlighting typical pitfalls and practical challenges arising when ...analyzing real data. Extensive simulations are used to demonstrate the reasons that render order selection particularly challenging in practice despite the conceptual simplicity of the task. In particular, we demonstrate why well-established formal procedures for model selection, such as those based on standard information criteria, tend to favor models with numbers of states that are undesirably large in situations where states shall be meaningful entities. We also offer a pragmatic step-by-step approach together with comprehensive advice for how practitioners can implement order selection. Our proposed strategy is illustrated with a real-data case study on muskox movement.
Herbivores are key drivers of vegetation dynamics in most ecosystems. However, the effect of high arctic herbivores on vegetation dynamics throughout a growing season is not well understood. In this ...study, we examine the impacts of a large dominant herbivore in the tundra ecosystem, the muskox, Ovibos moschatus, using exclosures established in a fen in high Arctic Greenland. Using weekly sampling throughout the growing season, we quantified the effects of muskox exclusion on aboveground plant biomass and on concentrations and pools of carbon and nitrogen, and explored the timing of peak biomass and nutrient pools. Excluding muskoxen profoundly changed plant abundances and dynamics of the fen, with more than a doubling of aboveground plant biomass and carbon and nitrogen pool sizes. Specifically, large increases in mosses and litter were observed, while graminoid biomass did not change significantly with exclusion of muskoxen. Excluding muskoxen advanced the peak of plant biomass, but also led to a more rapid decline, resulting in an earlier and shorter period of maximal plant biomass inside the exclosures. The largest impact of muskoxen on the arctic fen ecosystem seems to be through their trampling effects on the moss layer, which likely mediated most of the observed changes. This study demonstrates how quickly an ecosystem may respond to changes in the abundance of large herbivores and highlights their pivotal role in modifying vegetation dynamics and nutrient cycling in tundra ecosystems.
Processes leading to range contractions and population declines of Arctic megafauna during the late Pleistocene and early Holocene are uncertain, with intense debate on the roles of human hunting, ...climatic change, and their synergy. Obstacles to a resolution have included an overreliance on correlative rather than process‐explicit approaches for inferring drivers of distributional and demographic change. Here, we disentangle the ecological mechanisms and threats that were integral in the decline and extinction of the muskox (Ovibos moschatus) in Eurasia and in its expansion in North America using process‐explicit macroecological models. The approach integrates modern and fossil occurrence records, ancient DNA, spatiotemporal reconstructions of past climatic change, species‐specific population ecology, and the growth and spread of anatomically modern humans. We show that accurately reconstructing inferences of past demographic changes for muskox over the last 21,000 years require high dispersal abilities, large maximum densities, and a small Allee effect. Analyses of validated process‐explicit projections indicate that climatic change was the primary driver of muskox distribution shifts and demographic changes across its previously extensive (circumpolar) range, with populations responding negatively to rapid warming events. Regional analyses show that the range collapse and extinction of the muskox in Europe (~13,000 years ago) was likely caused by humans operating in synergy with climatic warming. In Canada and Greenland, climatic change and human activities probably combined to drive recent population sizes. The impact of past climatic change on the range and extinction dynamics of muskox during the Pleistocene–Holocene transition signals a vulnerability of this species to future increased warming. By better establishing the ecological processes that shaped the distribution of the muskox through space and time, we show that process‐explicit macroecological models have important applications for the future conservation and management of this iconic species in a warming Arctic.
We reconstructed 21,000 years of climate‐ and human‐driven range dynamics of muskox by integrating modern occurrence records, fossil records, paleoclimate reconstructions, ancient DNA sequences, human expansion models and spatially explicit process‐explicit macroecological models. Models that could reconcile inferences of demographic change from fossils were used to determine the likely chains of causality responsible for the contemporary distribution of muskox. We show that climatic change was a primary driver of the structure and dynamics of the distribution of muskox, with human activities, and their interactions with climatic changes, being important in some regions.
Understanding the role of interspecific interactions in shaping ecological communities is one of the central goals in community ecology. In fungal communities, measuring interspecific interactions ...directly is challenging because these communities are composed of large numbers of species, many of which are unculturable. An indirect way of assessing the role of interspecific interactions in determining community structure is to identify the species co‐occurrences that are not constrained by environmental conditions. In this study, we investigated co‐occurrences among root‐associated fungi, asking whether fungi co‐occur more or less strongly than expected based on the environmental conditions and the host plant species examined. We generated molecular data on root‐associated fungi of five plant species evenly sampled along an elevational gradient at a high arctic site. We analysed the data using a joint species distribution modelling approach that allowed us to identify those co‐occurrences that could be explained by the environmental conditions and the host plant species, as well as those co‐occurrences that remained unexplained and thus more probably reflect interactive associations. Our results indicate that not only negative but also positive interactions play an important role in shaping microbial communities in arctic plant roots. In particular, we found that mycorrhizal fungi are especially prone to positively co‐occur with other fungal species. Our results bring new understanding to the structure of arctic interaction networks by suggesting that interactions among root‐associated fungi are predominantly positive.
Insects provide key pollination services in most terrestrial biomes, but this service depends on a multistep interaction between insect and plant. An insect needs to visit a flower, receive pollen ...from the anthers, move to another conspecific flower, and finally deposit the pollen on a receptive stigma. Each of these steps may be affected by climate change, and focusing on only one of them (e.g., flower visitation) may miss important signals of change in service provision. In this study, we combine data on visitation, pollen transport, and single‐visit pollen deposition to estimate functional outcomes in the high Arctic plant‐pollinator network of Zackenberg, Northeast Greenland, a model system for global warming–associated impacts in pollination services. Over two decades of rapid climate warming, we sampled the network repeatedly: in 1996, 1997, 2010, 2011, and 2016. Although the flowering plant and insect communities and their interactions varied substantially between years, as expected based on highly variable Arctic weather, there was no detectable directional change in either the structure of flower‐visitor networks or estimated pollen deposition. For flower‐visitor networks compiled over a single week, species phenologies caused major within‐year variation in network structure despite consistency across years. Weekly networks for the middle of the flowering season emerged as especially important because most pollination service can be expected to be provided by these large, highly nested networks. Our findings suggest that pollination ecosystem service in the high Arctic is remarkably resilient. This resilience may reflect the plasticity of Arctic biota as an adaptation to extreme and unpredictable weather. However, most pollination service was contributed by relatively few fly taxa (Diptera: Spilogona sanctipauli and Drymeia segnis Muscidae and species of Rhamphomyia Empididae). If these key pollinators are negatively affected by climate change, network structure and the pollination service that depends on it would be seriously compromised.
Global change is causing drastic changes in the pollinator communities of the Arctic. While arctic flowers are visited by a wide range of insects, flies in family Muscidae have been proposed as a ...pollinator group of particular importance. To understand the functional outcome of current changes in pollinator community composition, we examined the role of muscids in the pollination of a key plant species, the mountain avens (Dryas). We monitored the seed set of Dryas across 15 sites at Zackenberg, northeast Greenland, and used sticky flower mimics and DNA barcoding to describe the flower-visiting community at each site. To evaluate the consequences of shifts in pollinator phenology under climate change, we compared the flower visitors between the early and the late season. Our approach revealed a diverse community of insects visiting Dryas, including two-thirds of all insect species known from the area. Even against this diverse background, the abundance of muscid flies emerged as a key predictor for seed set in Dryas, whereas overall insect abundance and species richness had little or no effect. With muscid flies as the main drivers of the pollinating function in the High Arctic, a recently observed decline in their abundances offers cause for concern.
Abstract
Recent research using repeat photography, long-term ecological monitoring and dendrochronology has documented shrub expansion in arctic, high-latitude and alpine tundra ecosystems. Here, we ...(1) synthesize these findings, (2) present a conceptual framework that identifies mechanisms and constraints on shrub increase, (3) explore causes, feedbacks and implications of the increased shrub cover in tundra ecosystems, and (4) address potential lines of investigation for future research. Satellite observations from around the circumpolar Arctic, showing increased productivity, measured as changes in ‘greenness’, have coincided with a general rise in high-latitude air temperatures and have been partly attributed to increases in shrub cover. Studies indicate that warming temperatures, changes in snow cover, altered disturbance regimes as a result of permafrost thaw, tundra fires, and anthropogenic activities or changes in herbivory intensity are all contributing to observed changes in shrub abundance. A large-scale increase in shrub cover will change the structure of tundra ecosystems and alter energy fluxes, regional climate, soil–atmosphere exchange of water, carbon and nutrients, and ecological interactions between species. In order to project future rates of shrub expansion and understand the feedbacks to ecosystem and climate processes, future research should investigate the species or trait-specific responses of shrubs to climate change including: (1) the temperature sensitivity of shrub growth, (2) factors controlling the recruitment of new individuals, and (3) the relative influence of the positive and negative feedbacks involved in shrub expansion.
Background: Management of major life-threatening bleeding with factor Xa (FXa) inhibition poses complex challenges involving novel direct reversal agents competing with non-specific preexisting ...strategies. The recent availability of andexanet alfa (AA) led to a health-system guideline incorporating its use alongside the most commonly used historic agent, four-factor prothrombin complex concentrate (4F-PCC). Objectives: The objective was to characterize the use and efficacy of AA and 4F-PCC for reversal of FXa inhibition after implementation of the health-system guideline. Methods: This multi-hospital, retrospective cohort study included patients aged >18 years administered either AA or 4F-PCC between October 2018 to June 2020 with the indication for urgent reversal of FXa inhibitor-induced coagulopathy. The primary outcome assessed hemostatic efficacy between treatment groups. Secondary outcomes evaluated adjunct blood product administration, incidence of repeat pharmacologic reversal, incidence of thromboembolism, intensive care unit and hospital length of stays, and in-hospital mortality. Results: Eighty-five patients were included; 33 patients received AA and 52 patients received 4F-PCC. Effective hemostasis was achieved at similar rates in both treatment groups (84.8% vs 76.9%; P = .373). Thrombotic events occurring during the observed hospitalization were more frequent among the AA treated group (18% vs 3.8%, P = .027). No differences were observed for other secondary outcomes. Conclusion: Guideline use resulted in similar rates of effective hemostasis with a higher incidence of VTE in patients receiving AA. Further exploration with a larger, prospective study to evaluate these findings is warranted.
The nutritional state of animals is tightly linked to the ambient environment, and for northern ungulates the state strongly influences vital population demographics, such as pregnancy rates. ...Continuously growing tissues, such as hair, can be viewed as dietary records of animals over longer temporal scales. Using sequential data on nitrogen stable isotopes (δ15N) in muskox guard hairs from ten individuals in high arctic Northeast Greenland, we were able to reconstruct the dietary history of muskoxen over approximately 2.5 years with a high temporal resolution of app. 9 days. The dietary chronology included almost three full summer and winter periods. The diet showed strong intra- and inter-annual seasonality, and was significantly linked to changes in local environmental conditions (temperature and snow depth). The summer diets were highly similar across years, reflecting a graminoid-dominated diet. In contrast, winter diets were markedly different between years, a pattern apparently linked to snow conditions. Snow-rich winters had markedly higher δ15N values than snow-poor winters, indicating that muskoxen had limited access to forage, and relied more heavily on their body stores. Due to the close link between body stores and calf production in northern ungulates, the dietary winter signals could eventually serve as an indicator of calf production the following spring. Our study opens the field for further studies and longer chronologies to test such links. The method of sequential stable isotope analysis of guard hairs thus constitutes a promising candidate for population-level monitoring of animals in remote, arctic areas.
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