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Scavenging can have important consequences for food web dynamics, for example, it may support additional consumer species and affect predation on live prey. Still, few food web models include scavenging. We develop a dynamic model that includes two facultative scavenger species, which we refer to as the predator or scavenger species according to their natural scavenging propensity, as well as live prey, and a carrion pool to show ramifications of scavenging for predation in simple food webs. Our modeling suggests that the presence of scavengers can both increase and decrease predator kill rates and overall predation in model food webs and the impact varies (in magnitude and direction) with context. In particular, we explore the impact of the amount of dynamics (exploitative competition) allowed in the predator, scavenger, and prey populations as well as the direction and magnitude of interference competition between predators and scavengers. One fundamental prediction is that scavengers most likely increase predator kill rates, especially if there are exploitative feedback effects on the prey or carrion resources like is normally observed in natural systems. Scavengers only have minimal effects on predator kill rate when predator, scavenger, and prey abundances are kept constant by management. In such controlled systems, interference competition can greatly affect the interactions in contrast to more natural systems, with an increase in interference competition leading to a decrease in predator kill rate. Our study adds to studies that show that the presence of predators affects scavenger behavior, vital rates, and food web structure, by showing that scavengers impact predator kill rates through multiple mechanisms, and therefore indicating that scavenging and predation patterns are tightly intertwined. We provide a road map to the different theoretical outcomes and their support from different empirical studies on vertebrate guilds to provide guidance in wildlife management., Scavenging, while often ignored, can have major impacts on predation and food web dynamics. We convert empirical observations on scavenging and predation into a theoretical framework to explain observed contrasting patterns and make predictions across different food webs. ​

Arctic ecosystems are changing dramatically with warmer and wetter conditions resulting in complex interactions between herbivores and their forage. We investigated how Svalbard reindeer (Rangifer tarandus platyrhynchus) modify their late winter diets in response to long-term trends and interannual variation in forage availability and accessibility. By reconstructing their diets and foraging niches over a 17-year period (1995–2012) using serum δ13C and δ15N values, we found strong support for a temporal increase in the proportions of graminoids in the diets with a concurrent decline in the contributions of mosses. This dietary shift corresponds with graminoid abundance increases in the region and was associated with increases in population density, warmer summer temperatures and more frequent rain-on-snow (ROS) in winter. In addition, the variance in isotopic niche positions, breadths, and overlaps also supported a temporal shift in the foraging niche and a dietary response to extreme ROS events. Our long-term study highlights the mechanisms by which winter and summer climate changes cascade through vegetation shifts and herbivore population dynamics to alter the foraging niche of Svalbard reindeer. Although it has been anticipated that climate changes in the Svalbard region of the Arctic would be detrimental to this unique ungulate, our study suggests that environmental change is in a phase where conditions are improving for this subspecies at the northernmost edge of the Rangifer distribution.

Global temperatures are increasing, afecting timing and availability of vegetation along with relationships between plants and their consumers. We examined the efect of population density, herd body condition in the previous year, elevation, plant productivity and phenology, snow, and winter onset on juvenile body mass in 63 semi-domesticated populations of Rangifer tarandus throughout Norway using spatiotemporal generalized additive models (GAMs) and varying coefcient models (VCMs). Optimal climate windows were calculated at both the regional and national level using a novel nonlinear climate window algorithm optimized for prediction. Spatial and temporal variation in efects of population and environmental predictors were considered using a model including covariates decomposed into spatial, temporal, and residual components. The performance of this decomposed model was compared to spatiotemporal GAMs and VCMs. The decomposed model provided the best ft and lowest prediction errors. A positive efect of herd body condition in the previous year explained most of the deviance in calf body mass, followed by a more complex efect of population density. A negative efect of timing of spring and positive efect of winter onset on juvenile body mass suggested that a snow free season was positive for juvenile body mass growth. Our fndings suggest early spring onset and later winter permanent snow cover as reinforcers of early-life conditions which support more robust reindeer populations. Our methodological improvements for climate window analyses and efect size measures for decomposed variables provide important contributions to account for, measure, and interpret nonlinear relationships between climate and animal populations at large scales. Climate window · Decomposed covariates · Generalized additive models · Plant productivity · Reindeer · Varying coefcient models

1.The cost of reproduction on demographic rates is often assumed to operate through changing body condition. Several studies have found that reproduction depresses body mass more if the current conditions are severe, such as high population densities or adverse weather, than under benign environmental conditions. However, few studies have investigated the association between the fitness components and body mass costs of reproduction. 2.Using 25 years of individual-based capture–recapture data from Svalbard reindeer Rangifer tarandus platyrhynchus, we built a novel Bayesian state-space model that jointly estimated interannual change in mass, annual reproductive success and survival, while accounting for incomplete observations. The model allowed us to partition the differential effects of intrinsic and extrinsic factors on both non-reproductive mass change and the body mass cost of reproduction, and to quantify their consequences on demographic rates.3. Contrary to our expectation, the body mass cost of reproduction (mean = –5.8 kg) varied little between years (CV = 0.08), whereas the between-year variation in body mass changes, that were independent of the previous year's reproductive state, varied substantially (CV = 0.4) in relation to autumn temperature and the amount of rain-on-snow in winter. This body mass loss led to a cost of reproduction on the next reproduction, which was amplified by the same environmental covariates, from a 10% reduction in reproductive success in benign years, to a 50% reduction in harsh years. The reproductive mass loss also resulted in a small reduction in survival.4. Our results show how demographic costs of reproduction, driven by interannual fluctuations in individual body condition, result from the balance between body mass costs of reproduction and body mass changes that are independent of previous reproductive state. We illustrate how a strong context-dependent fitness cost of reproduction can occur, despite a relatively fixed body mass cost of reproduction. This suggests that female reindeer display a very conservative energy allocation strategy, either aborting their reproductive attempt at an early stage or weaning at a relatively constant cost. Such a strategy might be common in species living in a highly stochastic and food limited environment.

Significance Whether the renowned population cycles of small mammals in northern food webs are driven by bottom-up (plant–herbivore) or top-down (predator–prey) interactions is still a debated question but crucial to our understanding of their ecological functions and response to climate change. A long-term study of a graminivorous vole population in an exceptionally simple High Arctic food web allowed us to identify which population dynamics features are present without top-down regulation. Unique features were high-amplitude, noncyclic population fluctuations driven by a combination of stochastic weather events and season-specific density dependence likely arising from plant–herbivore interactions. That such features are not present in more complex food webs points to the importance of top-down regulation in small mammal populations., Ecologists are still puzzled by the diverse population dynamics of herbivorous small mammals that range from high-amplitude, multiannual cycles to stable dynamics. Theory predicts that this diversity results from combinations of climatic seasonality, weather stochasticity, and density-dependent food web interactions. The almost ubiquitous 3- to 5-y cycles in boreal and arctic climates may theoretically result from bottom-up (plant–herbivore) and top-down (predator–prey) interactions. Assessing, empirically, the roles of such interactions and how they are influenced by environmental stochasticity has been hampered by food web complexity. Here, we take advantage of a uniquely simple High Arctic food web, which allowed us to analyze the dynamics of a graminivorous vole population not subjected to top-down regulation. This population exhibited high-amplitude, noncyclic fluctuations—partly driven by weather stochasticity. However, the predominant driver of the dynamics was overcompensatory density dependence in winter that caused the population to frequently crash. Model simulations showed that the seasonal pattern of density dependence would yield regular 2-y cycles in the absence of stochasticity. While such short cycles have not yet been observed in mammals, they are theoretically plausible if graminivorous vole populations are deterministically bottom-up regulated. When incorporating weather stochasticity in the model simulations, cyclicity became disrupted and the amplitude was increased—akin to the observed dynamics. Our findings contrast with the 3- to 5-y population cycles that are typical of graminivorous small mammals in more complex food webs, suggesting that top-down regulation is normally an important component of such dynamics.

In animals with long generation times, evolution of physiological and morphological traits may not be fast enough to keep up with rapid climate warming, but thermoregulatory behaviour can possibly serve as an important buffer mitigating warming effects. In this study, we investigated if the cold-adapted Svalbard reindeer (Rangifer tarandus platyrhynchus (Vrolik, 1829)) used cool bed sites as a thermoregulatory behaviour in the summer. We recorded habitat variables and ground temperature at 371 bed sites with random “control” sites 10 and 100 m distant. Using case-control logistic regression, we found that reindeer selected bed sites on cool substrates (snow and mire), as well as cold, dry ground on days with warm ambient temperatures, while they avoided such sites on cold days. Selection of both cool substrates and cool ground did not depend on age or sex. The study was conducted in an environment where neither predatory threat nor insect harassment influenced bed site selection. Our findings suggest that the thermal landscape is important for habitat selection of cold-adapted Arctic ungulates in summer. Thus, behavioural strategies may be important to mitigate effects of climate change, at least in the short term. bed site, behavioural buffering, climate change, habitat selection, snow, ungulates, Svalbard reindeer, Rangifer tarandus platyrhynchus.

Human-caused habitat disturbances and climate change are leading threats to biodiversity. Studying the impacts of human activities on wildlife from a behavioral perspective is a relevant starting point to understand the mechanisms underlying population and species resistance and resilience to disturbances. In this study, we assessed the effects of weather (temperature and precipitation), habitat disturbances (roads and clearcuts), and natural habitat types on the space use patterns of a threatened boreal population of woodland caribou (Rangifer tarandus caribou). An extensive data set of 288,665 relocations from 50 adult females outfitted with GPS collars over 7 years in the boreal forest of Québec, Canada was used to evaluate residency time in natural and disturbed habitats for five distinct biologically defined periods. The most parsimonious linear mixed-effects model for each period showed that individuals stayed longer in more natural habitat types. During calving and summer, residency time decreased with increasing road density, whereas residency time decreased with increasing temperature during winter and spring. We found no evidence of a synergistic effect between daily weather and human disturbances on movement behavior of caribou, but consider their respective influence as additive. We also showed large individual variation in residency time, except during the calving period. Lower individual variation in residency time during calving may be explained by strong evolutionary constraints on behavior faced by females to ensure protection and survival of their offspring. Based on our results, we suggest keeping large patches of suitable and roadless habitat for caribou to favor the spacing-out antipredator strategy exhibited by females during calving. By tracking individuals over several complete annual cycles, we showed variation in the effects of daily weather and human disturbances on residency time across biological periods. Our study highlights that the inclusion of daily weather variables helps better understand space-use patterns of a threatened species.

Assessing the effectiveness of conservation actions to halt population declines is challenging when confounded by other factors. We assessed whether culling of red fox, a predator currently increasing in number in the sub‐Arctic, contributed to recent recovery of the critically endangered Fennoscandian population of Lesser White‐fronted Goose Anser erythropus, while controlling for potentially confounding food web dynamics. Using 19 years of data, 10 before and 9 after the implementation of annual red fox culling, we estimated the effect of this action on annual performance of the goose population. We corrected for the potentially confounding effects of cyclic rodent dynamics and semi‐domestic reindeer carrion abundance, both of which are expected to trigger predator functional and numerical responses, as well as for annual variation in spring phenology. Goose reproductive success fluctuated in synchrony with the rodent cycle and was negatively related to abundant carrion. When accounting for these aspects of food web dynamics, there was no evidence for an effect of red fox culling on reproductive success. There was, however, a tendency for fox culling to increase adult survival. Our analysis suggests that goose performance in their breeding area is influenced by fluctuating offspring predation, mediated by mainly natural (rodents) and partly anthropogenic (semi‐domestic reindeer) dynamic components of the food web. Synthesis and applications. The effect of a decade‐long red fox culling on goose reproductive success and survival is currently uncertain, despite predation driving reproductive success through changes in rodent and reindeer carrion abundance. New management actions may consist of regulation of reindeer herd sizes and/or removal of carcasses to reduce the subsidizing effect of reindeer carrion on mesopredators. Getting robust evidence regarding the impact of red fox culling on population recovery depends on continuing research to disentangle food web dynamics and efficiency of management actions.

The fasting endurance hypothesis (FEH) predicts strong selection for large body size in mammals living in environments where food supply is interrupted over prolonged periods of time. The Arctic is a highly seasonal and food restricted environment, but contrary to predictions from the FEH, empirical evidence shows that Arctic mammals are often smaller than their temperate conspecifics. Intraspecific studies integrating physiology and behaviour of different‐sized individuals, may shed light on this paradox. We tested the FEH in free‐living Svalbard reindeer (Rangifer tarandus platyrhynchus). We measured daily energy expenditure (DEE), subcutaneous body temperature (Tsc) and activity levels during the late winter in 14 adult females with body masses ranging from 46.3 to 57.8 kg. Winter energy expenditure (WEE) and fasting endurance (FE) were modelled dynamically by combining these data with body composition measurements of culled individuals at the onset of winter (14 years, n = 140) and variation in activity level throughout winter (10 years, n = 70). Mean DEE was 6.3±0.7 MJ day−1. Lean mass, Tsc and activity had significantly positive effects on DEE. Across all 140 individuals, mean FE was 85±17 days (range 48–137 days). In contrast to the predictions of the FEH, the dominant factor affecting FE was initial fat mass, while body mass and FE were not correlated. Furthermore, lean mass and fat mass were not correlated. FE was on average 80% (45 days) longer in fat than lean individuals of the same size. Reducing activity levels by ~16% or Tsc by ~5% increased FE by 7%, and 4%, respectively. Our results fail to support the FEH. Rather, we demonstrate that (i) the size of fat reserves can be independent of lean mass and body size within a species, (ii) ecological and environmental variation influence FE via their effects on body composition, and (iii) physiological and behavioural adjustments can improve FE within individuals. Altogether, our results suggest that there is a selection in Svalbard reindeer to accumulate body fat, rather than to grow structurally large. he Arctic, activity, biologging, daily energy expenditure, doubly labelled water, intraspecific scaling, subcutaneous body temperature, Svalbard reindeer to accumulate body fat, rather than to grow structurally large.

Ecologists are still puzzled by the diverse population dynamics of herbivorous small mammals that range from high-amplitude, multi-annual cycles to stable dynamics. Theory predicts that this diversity results from combinations of climatic seasonality, weather stochasticity and density-dependent food web interactions. The almost ubiquitous 3-5-yr cycles in boreal and arctic climates may theoretically result from bottom-up (plant-herbivore) and top-down (predator-prey) interactions. Assessing empirically the roles of such interactions, and how they are influenced by environmental stochasticity, has been hampered by food web complexity. Here, we take advantage of a uniquely simple High-Arctic food web, which allowed us to analyze dynamics of a graminivorous vole population not subjected to top-down regulation. This population exhibited high-amplitude, non-cyclic fluctuations - partly driven by weather stochasticity. However, the predominant driver of the dynamics was direct density dependence, which alternated between being weak in summer and strong (overcompensatory) in winter that the population frequently crashed. Model simulations showed that this season-specific density dependence would yield regular 2-year cycles in absence of stochasticity. While such short cycles have not yet been observed in mammals, they are theoretically plausible if graminivorous vole populations are deterministically bottom-up regulated. When incorporating weather stochasticity in the model simulations, cyclicity became disrupted and the amplitude was increased - akin to the observed dynamics. Our findings contrast with the 3-5-yr population cycles involving delayed density dependence that are typical of graminivorous small mammals in more complex food webs, suggesting that top-down regulation is an important component of such dynamics.

Predator avoidance and food availability are both factors known to influence habitat selection and site fidelity around calving in caribou and reindeer. Here, we assess habitat selection and site fidelity during the calving period in the solitary, Arctic Svalbard reindeer Rangifer tarandus platyrhynchus, which is subject to limited predation risk and human disturbance. In this largely predator-free environment, we explore and discuss if habitat selection during the first week after calving is driven by food availability or remnants of anti-predatory behaviour. Based on GPS-collar data and ultrasound scanning (2009–2017; n = 134 individual-years) from two study areas, we estimated individual calving dates using recursive partitioning and first passage time and compared habitat selection and site fidelity of reproductive versus non-reproductive females. The K-select analysis suggested similar habitat selection during calving in reproductive and non-reproductive females. Female reindeer generally selected for lowland, flat habitats with high proportion of heath and moss tundra, i.e. habitats typically rich in terms of forage plants. Individuals producing a calf had significantly higher site fidelity in the calving period compared to the null model, and the mean distance between consecutive years' calving areas ranged between 1.5 and 3.9 km. Our study provides support for the prediction that in the absence of significant predation, ungulate calving site selection in the Arctic is mainly driven by the availability of spatially and temporally varying food resources.

The strikingly diverse population dynamics of herbivorous small mammals, ranging from high-amplitude, multi-annual cycles to relatively stable dynamics, have puzzled ecologists for a century. Theory predicts that this diversity is shaped by density-dependent food web interactions and stochastic weather events. Recent disrupted cycles through amplitude dampening have been attributed to climate change. However, empirical testing has been hampered by the complexity of the food webs in which these herbivores normally are found. Here we analyze population dynamics of a grazing vole species in a uniquely simple high-Arctic food web without top-down regulation. In accordance with theory, the population dynamics was mostly ruled by overcompensatory density-dependence in winter that without environmental stochasticity would have yielded seasonality driven high-amplitude 2-year cycles. In this simple food web, rain-on-snow events disrupted cyclicity, but not through amplitude dampening. Our case study highlights how food web structure may modify the impact of climate change on population dynamics.

We point out problems with the article Productivity beyond density: A critique of management models for reindeer pastoralism in Norway by Marin and co-workers published in Pastoralism in 2020. In our opinion, there are several misleading claims about the governance of the reindeer pastoralist system in Norway, the Røros model for herd management and density dependence in reindeer herds in their article. We point out the errors in their empirical re-evaluation of previous work on the relationship between reindeer densities and the productivity and slaughter weights in herds. These errors have a significant bearing on their conclusions. We agree that weather variability has a substantial impact on reindeer body mass growth, fecundity and survival, but disagree with Marin et al. when they argue that reindeer densities are of minor importance for reindeer productivity and animal welfare.

The impact of climate change on the dynamics of populations has been well documented and is widespread. However, weather variability influences populations both directly and indirectly, and is mediated by species interactions. This complexity may impede proper climate impact assessments. Hence, predicting the consequences of climate change may require including processes that occur both with time lags and across trophic levels. Based on our current understanding of the mechanisms linking local climate and trophic interactions in tundra ecosystems, we used a state-space formulation of a mediation model that allowed for assessing the relative contribution of direct and indirect environmental (weather and trophic) effects on reindeer Rangifer tarandus reproductive success. Our study showed that the mediator effect of body condition caused delayed but predictable effects of weather, plant productivity, and reindeer densities on reproductive success. Furthermore, these predictors also affected reproductive success directly and with the same sign, suggesting that direct and indirect effects pulled in the same direction with respect to their combined total effect on reproductive success. Hence, poor weather conditions not only affect calf production negatively the same year, but also increase the likelihood of poor reproductive success the subsequent year. The results support the expectation that calf slaughter mass (as a proxy for herd body condition) is an important indicator of the state of reindeer herds with respect to their production potential and resilience to weather events and climate change. Finally, the model framework employed in the present study can be further developed as a potential vehicle for near-term forecasting, and thereby constitutes a useful tool for adaptive management.

Seasonal energetic challenges may constrain an animal's ability to respond to changing individual and environmental conditions. Here, we investigated variation in heart rate, a well-established proxy for metabolic rate, in Svalbard reindeer (Rangifer tarandus platyrhynchus), a species with strong seasonal changes in foraging and metabolic activity. In 19 adult females, we recorded heart rate, subcutaneous temperature and activity using biologgers. Mean heart rate more than doubled from winter to summer. Typical drivers of energy expenditure, such as reproduction and activity, explained a relatively limited amount of variation (2–6% in winter and 16–24% in summer) compared to seasonality, which explained 75% of annual variation in heart rate. The relationship between heart rate and subcutaneous temperature depended on individual state via body mass, age and reproductive status, and the results suggested that peripheral heterothermy is an important pathway of energy management in both winter and summer. While the seasonal plasticity in energetics makes Svalbard reindeer well-adapted to their highly seasonal environment, intraseasonal constraints on modulation of their heart rate may limit their ability to respond to severe environmental change. This study emphasizes the importance of encompassing individual state and seasonal context when studying energetics in free-living animals.This article is part of the theme issue ‘Measuring physiology in free-living animals (Part II)’.

Arctic ungulates are experiencing the most rapid climate warming on Earth. While concerns have been raised that more frequent icing events may cause die-offs, and earlier springs may generate a trophic mismatch in phenology, the effects of warming autumns have been largely neglected. We used 25 years of individual-based data from a growing population of wild Svalbard reindeer, to test how warmer autumns enhance population growth. Delayed plant senescence had no effect, but a six-week delay in snow-onset (the observed data range) was estimated to increase late winter body mass by 10%. Because average late winter body mass explains 90% of the variation in population growth rates, such a delay in winter-onset would enable a population growth of r = 0.20, sufficient to counteract all but the most extreme icing events. This study provides novel mechanistic insights into the consequences of climate change for Arctic herbivores, highlighting the positive impact of warming autumns on population viability, offsetting the impacts of harsher winters. Thus, the future for Arctic herbivores facing climate change may be brighter than the prevailing view. body mass, climate change, fitness, GPS, movement ecology, plant phenology, Rangifer, snow, space use, ungulates © 2020 The Authors. Global Change Biology published by John Wiley & Sons Ltd This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Question: Vascular plant productivity of arctic tundra has often been viewed as varying little between years and thus being largely insensitive to the high inter-annual variation in summer weather conditions. Yet, remote-sensing data and retrospective growth analyses of the circumpolar dwarf shrub, Cassiope tetragona, commonly show considerable between-year variability in plant growth in response to variation in summer temperature. Given that both Cassiope growth and vascular plant biomass production share a common environmental driver, summer temperature, we would expect positive co-variation between them. Here we investigate whether this is indeed the case and if so over what spatial scale. Location: Nordenskiöldland, high arctic Svalbard. Methods: We brought dendroecology and plot-based field estimation methodologies together in an empirical study using retrospective analysis of Cassiope growth and annual estimation of above-ground vegetation biomass production to investigate their temporal and spatial co-variation and sensitivity to summer weather conditions. Results: Despite substantial small-scale heterogeneity, we found spatial co-variation in Cassiope growth patterns, which weakened as distance between sampling sites increased from 0 to 25 km. Furthermore, we found a strong positive correlation between annual estimates of above-ground live vascular plant biomass and Cassiope shoot growth over a 12-year period at a local scale. The correlation declined with distance, likely due to increasing differences in local weather conditions. Conclusions: We demonstrate that Cassiope growth can be used as a proxy for above-ground tundra vegetation productivity at the local scale. Our findings suggest that Arctic plant productivity is as sensitive to between-year variation in summer temperature as the well-established growth response of Cassiope. This challenges the view that tundra plant productivity varies little between years and provides a mechanistic understanding that helps reconcile field-and satellite-based annual estimation methods. K E Y W O R D S Arctic bell-heather, arctic climate change, Cassiope tetragona, dendrochronology, plant– climate interaction, spatial scale, Svalbard, tundra vegetation, vascular plant productivity, vegetation biomass

Sustainable management of wildlife populations can be aided by building models that both identify current drivers of natural dynamics and provide near-term predictions of future states. We employed a Strategic Foresight Protocol (SFP) involving stakeholders to decide the purpose and structure of a dynamic state-space model for the population dynamics of the Willow Ptarmigan, a popular game species in Norway. Based on local knowledge of stakeholders, it was decided that the model should include food web interactions and climatic drivers to provide explanatory predictions. Modeling confirmed observations from stakeholders that climate change impacts Ptarmigan populations negatively through intensified outbreaks of insect defoliators and later onset of winter. Stakeholders also decided that the model should provide anticipatory predictions. The ability to forecast population density ahead of the harvest season was valued by the stakeholders as it provides the management extra time to consider appropriate harvest regulations and communicate with hunters prior to the hunting season. Overall, exploring potential drivers and predicting short-term future states, facilitate collaborative learning and refined data collection, monitoring designs, and management priorities. Our experience from adapting a SFP to a management target with inherently complex dynamics and drivers of environmental change, is that an open, flexible, and iterative process, rather than a rigid step-wise protocol, facilitates rapid learning, trust, and legitimacy. climate change; decision-making; food web; harvesting; near-term forecasting; population cycles; stakeholders; strategic foresight.

Theory predicts that animal populations will be synchronized over large distances by weather and climatic conditions with high spatial synchrony. However, local variation in population responses to weather, and low synchrony in key weather variables or in other ecological processes may reduce the population synchrony. We investigated to what extent temperature and precipitation during different periods of the year synchronized juvenile body mass of moose and reindeer in Norway. We expected high synchronizing effect of weather variables with a high and consistent explanatory power on body mass dynamics across populations, and a weaker synchronizing effect of weather variables whose effect on body mass varied among populations. Juvenile body mass in both species was related to temperature and precipitation during several periods of the year. Temperature had the strongest explanatory power in both species, with a similar effect across all populations. There was higher spatial synchrony in temperature compared to precipitation, and accordingly temperature had the strongest synchronizing effect on juvenile body mass. Moreover, periods with strong explanatory power had stronger synchronizing effect on juvenile body mass in both species. However, weather variables with large variation in the effects on body mass among populations had weak synchronizing effect. The results confirm that weather has a large impact on the spatial structure of population properties but also that spatial heterogeneity, for instance, in environmental change or population density may affect how and to what extent populations are synchronized.

Warming of the Arctic has resulted in earlier snowmelt and green-up of plants in spring, potentially disrupting the synchrony between plant phenology and breeding phenology in herbivores. A negative relationship between offspring survival in West Greenland caribou and the timing of vegetation emergence was the first finding of such a mismatch in Arctic mammals. However, other studies indicate that the energy for foetal growth and early lactation is predominantly drawn from stored energy reserves typical of ‘capital’ breeders, suggesting that conditions well before spring influence calf production more than the timing of spring onset. Here we use 20 years of observations of marked Svalbard reindeer to evaluate determinants of annual recruitment, as measured by the presence of a calf at foot in mid-summer. Spring temperatures and the enhanced vegetation index were used as proxies for spring onset, while data on body mass and pregnancy rates in late winter allowed us to determine maternal condition and the reproductive status before spring. Pregnancy rate, offspring survival and annual recruitment were all strongly correlated with average late winter adult female body mass (r = 0.87; r = 0.83; r = 0.92, respectively). Contrary to the findings in West Greenland, neither early calf survival nor annual recruitment were correlated with the two measures of annual variation in spring phenology (r = – 0.07, p = 0.8 and r = – 0.15, p = 0.6, respectively). We also revisit the Greenland data and reveal that the pattern of covariance between early and late measures of fecundity, as well as between early measures of fecundity and offspring survival, correspond with the results from Svalbard. Our results emphasize that conditions affecting maternal body mass during winter explain close to all the variation in recruitment, questioning the importance of the role of a mismatch between plant phenology and calving date.

Migratory prey is a widespread phenomenon that has implications for predator – prey interactions. By creating large temporal variation in resource availability between seasons it becomes challenging for carnivores to secure a regular year-round supply of food. Some predators may respond by following their migratory prey, however, most predators are sedentary and experience strong seasonal variation in resource availability. Increased predation on alternative prey may dampen such seasonal resource fl uctuations, but reduced reproduction rates in predators is a predicted consequence of migratory primary prey behavior that has received little empirical attention. We used data from 23 GPS collared Eurasian lynx Lynx lynx monitored during 2007 – 2013 in northern Norway, to examine how spatio-temporal variation in the migratory behavior of semi-domestic reindeer Rangifer tarandus infl uences lynx spatial organization and reproductive success using estimates of seasonal home range overlap and breeding success. We found that lynx of both sexes maintained seasonally stable home ranges and exhibited site fi delity across years, independent of whether they had access to reindeer throughout the year or experienced a scarcity of reindeer in winter due to migration. However, lynx without access to reindeer in winter showed a decreased probability of reproducing and a tendency for lowered kitten survival into their fi rst winter, when compared to female lynx with reindeer available year around. Th is supports the hypothesis that sedentary predators experience demographic costs in systems with migratory primary prey. Changes in the migratory behavior of ungulates, including disrupted migrations, is therefore likely to have bottom – up eff ects on the population dynamics of sedentary predators as well as the previously documented consequences for ungulate population dynamics.

Several caribou and reindeer (Rangifer tarandus) populations have experienced recent population declines, often attributed to anthropogenic stressors such as harvesting, landscape fragmentation, and climate change. Svalbard reindeer (R. t. platyrhynchus), the wild reindeer subspecies endemic to the high‐Arctic Svalbard archipelago, was protected in 1925, after most subpopulations had been eradicated by harvest. Although direct pressure from harvest has ceased, indirect anthropogenic stressors from environmental changes have increased in this climate change hot spot. An assessment of the current distribution and abundance is therefore urgently needed. We combined distance sampling (300 km transects, n = 489 reindeer groups) and total counts (1,350 km2, n = 1,349 groups) to estimate the Svalbard reindeer distribution and abundance across its entire range, which we compared with historical data from the literature and radiocarbon‐dated bones. Reindeer have now recolonized nearly all non‐glaciated land (i.e., areas occupied prior to human presence), and their spatial variation in abundance reflects vegetation productivity. Independent of vegetation productivity, however, recently recolonized areas have lower reindeer densities than areas not subject to past extirpation. This suggests that recovery from past overharvesting is still in progress. These incompletely recovered areas are potential targets for increased monitoring frequency and maintaining strict conservation to follow the Svalbard management goal (i.e., virtually untouched wilderness areas). Because of such ongoing recolonization, possibly combined with vegetation greening effects of recent warming, our status estimate of Svalbard reindeer abundance (22,435 [95% CI = 21,452–23,425]) is more than twice a previous estimate based on opportunistic counts. Thus, although our study demonstrates the successful outcome of strict harvesting control implemented a century ago, current and future population trajectories are likely shaped by climate change.

Extreme climate events often cause population crashes but are difficult to account for in population-dynamic studies. Especially in long-lived animals, density dependence and demography may induce lagged impacts of perturbations on population growth. In Arctic ungulates, extreme rain-on-snow and ice-locked pastures have led to severe population crashes, indicating that increasingly frequent rain-on-snow events could destabilize populations. Here, using empirically parameterized, stochastic population models for High-Arctic wild reindeer, we show that more frequent rain-on-snow events actually reduce extinction risk and stabilize population dynamics due to interactions with age structure and density dependence. Extreme rain-on-snow events mainly suppress vital rates of vulnerable ages at high population densities, resulting in a crash and a new population state with resilient ages and reduced population sensitivity to subsequent icy winters. Thus, observed responses to single extreme events are poor predictors of population dynamics and persistence because internal density-dependent feedbacks act as a buffer against more frequent events., Extreme climate events can cause population crashes and may threaten population persistence. Here, the authors model reindeer population dynamics and find that more frequent extremely icy winters can actually reduce extinction risk due to density dependence and a demographic shift to resilient ages.

Early-life environmental conditions may generate cohort differences in individual fitness, subsequently affecting population growth rates. Three, nonmutually exclusive hypotheses predict the nature of these fitness differences: (1) silver spoon effects, where individuals born in good conditions perform better across the range of adult environments; (2) the “environmental saturation” hypothesis, where fitness differences only occur in intermediate adult environmental conditions; and (3) the “environmental matching” or “predictive adaptive response” (PAR) hypothesis, where fitness is highest when adult environmental conditions match those experienced in early life. We quantified the context-dependent effect of early-life environment on subsequent reproductive success, survival, and population growth rate (k) of Svalbard reindeer, and explored how well it was explained by the three hypotheses. We found that good early-life conditions increased reproductive success compared to poor early-life conditions, but only when experiencing intermediate adult environmental conditions. This is the first example of what appears to be both “beneficial” and “detrimental environmental saturation” in a natural system. Despite weak early-life effects on survival, cohorts experiencing good early-life conditions contributed to higher population growth rates, when simulating realistic variation in adult environmental conditions. Our results show how the combination of a highly variable environment and biological constraints on fitness components can suppress silver spoon effects at both extremes of the adult environmental gradient. beneficial saturation; cohort; delayed environmental effect; detrimental saturation; environmental matching; fitness; predictive adaptive response; reindeer; silver spoon.

Environmental variation can generate life-long similarities among individuals born in the same breeding event, so-called cohort effects. Studies of cohort effects have to account for the potentially confounding effects of current conditions (observation year) and age of individuals. However, estimation of such models is hampered by inherent collinearity, as age is the difference between observation year (period) and cohort year. The difficulties of separating linear trends in any of the three variables in Age-Period-Cohort (APC) models are the subject of ongoing debate in social sciences and medicine but have remained unnoticed in ecology. After reviewing the use of APC models, we investigate the consequences of model specification on the estimation of cohort effects, using both simulated data and empirical data from a long-term individual-based study of reindeer in Svalbard. We demonstrate that APC models are highly sensitive to the model's treatment of age, period and cohort, which may generate spurious temporal trends in cohort effects. Avoiding grouping ages and using environmental covariates believed to be drivers of temporal variation reduces the APC identification problem. Nonetheless, ecologists should use caution, given that the specification issues in APC models may have substantial impacts on estimated effect sizes and therefore conclusions.

The costs of reproduction are important in shaping individual life histories, and hence population dynamics, but the mechanistic pathways of such costs are often unknown. Female reindeer have evolved antlers possibly due to interference competition on winter-feeding grounds. Here, we investigate if variation in antler size explains part of the cost of reproduction in late winter mass of female reindeer. We captured 440 individual Svalbard reindeer a total of 1426 times over 16 years and measured antler size and body mass in late winter, while presence of a ‘calf-at-heel’ was observed in summer. We found that reproductive females grew smaller antlers and weighed 4.3 kg less than non-reproductive females. Path analyses revealed that 14% of this cost of reproduction in body mass was caused by the reduced antler size. Our study is therefore consistent with the hypothesis that antlers in female Rangifer have evolved due to interference competition and provides evidence for antler growth as a cost of reproduction in females. Antler growth was constrained more by life history events than by variation in the environment, which contrasts markedly with studies on male antlers and horns, and hence increases our understanding of constraints on ornamentation and life history trade-offs.

The management and recovery of large predator populations in areas where human persecution has driven them to ecological extinction requires a solid understanding of the effects of both predation and food limitation on prey populations. We used 11 yr of data on reported losses among 17.3 million free-ranging sheep Ovis aries in the Norwegian farming industry to elucidate the relative roles of climate, vegetation characteristics, sheep densities, lamb body mass and densities of predators and alternative prey on the number of lambs and ewes lost on summer pastures. We first examined whether predator densities predicted autumn lamb body mass through possible impacts of predators on body growth (non-lethal effects) but found no evidence for such effects in our study system. This might be due to weak anti-predator behavioral responses in domesticated sheep. However, autumn lamb body mass was predicted by both sheep density and winter and spring weather conditions, probably through food availability. Losses of both lambs and ewes were positively and strongly related to the density of Eurasian lynx Lynx lynx, wolverine Gulo gulo and brown bear Ursus arctos. In addition, food availability and spring weather conditions were associated to losses of lambs, while precipitation in May predicted losses of ewes. There was little evidence for interaction effects of predator species on losses, suggesting that most of the effects of the predators were additive to each other. Given the strong effect of predator densities on sheep losses, we conclude that changing livestock husbandry practices towards a system that actively protects sheep and/or active management of predator densities may be necessary to reduce sheep losses where predators are recolonizing.