The neglected season: Warmer autumns counteract harsher winters and promote population growth in Arctic reindeer

Loe, Leif Egil; Liston, Glen E.; Pigeon, Gabriel; Barker, Kristin J.; Horvitz, Nir; Stien, Audun; Forchhammer, Mads C.; Getz, Wayne M.; Irvine, R. Justin; Lee, Aline Magdalena; Movik, Lars Kvam; Mysterud, Atle; Pedersen, Åshild Ønvik; Reinking, Adele K.; Ropstad, Erik; Trondrud, Liv Monica; Tveraa, Torkild; Veiberg, Vebjørn; Hansen, Brage Bremset; Albon, Steve

doi:10.1111/gcb.15458

Cited by 39 publications

(43 citation statements)

References 66 publications

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“…Changes in the Arctic's weather patterns and overall climate present additional challenges to caribou and reindeer populations (Loe et al 2020). Due to Arctic amplification, northern latitudes are warming nearly twice as fast as the rest of the world (Coumou et al 2018), and temperatures are projected to continue rising throughout this century (IPCC 2013).…”

Section: Introductionmentioning

confidence: 99%

Snowier winters extend autumn availability of high‐quality forage for caribou in Arctic Alaska

et al. 2021

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Section: Introductionmentioning

confidence: 99%

Snowier winters extend autumn availability of high‐quality forage for caribou in Arctic Alaska

et al. 2021

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“…For example, non‐lactating females in October were ~5% heavier than lactating females, suggesting that lactation hinders greater accumulation of body fat (Albon et al., 2017). Furthermore, later onset of snow in autumn has been shown to positively influence late winter body mass (Loe et al., 2021). Consequently, the high seasonality in energy supply and stochasticity during winter likely contributes to shaping a selection for fat and small phenotypes in Svalbard reindeer.…”

Section: Discussionmentioning

confidence: 99%

“…Second, ecological factors may be more important in influencing the size of internal body stores than structural size. In seasonal environments where food availability varies throughout the year, the amount of resources available largely determines the degree of fattening prior to the food‐depleted season (Loe et al., 2021; Pagano et al., 2018). In periods of low resource availability body mass declines, largely driven by the depletion of fat stores (Reimers & Ringberg, 1982).…”

Section: Introductionmentioning

confidence: 99%

“…Still, Svalbard reindeers’ fat reserves are insufficient to cover the energy demands over of the entire winter and must be subsidised by food intake (Tyler, 1987) in a season when snow and ice conditions restrict access to forage. Late winter body mass explains most of the annual variation in reproduction and survival, and is negatively related to, both early onset of snow in the autumn (Loe et al., 2021) and the severity of rain‐on‐snow in the subsequent winter (Albon et al., 2017). From the predictions of the FEH, long periods of low food availability, coupled with abrupt food shortage, should have led to a selection for a large body size.…”

Section: Introductionmentioning

confidence: 99%

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Fat storage influences fasting endurance more than body size in an ungulate

et al. 2021

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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. 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 (a) the size of fat reserves can be independent of lean mass and body size within a species, (b) ecological and environmental variation influence FE via their effects on body composition and (c) 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. A free Plain Language Summary can be found within the Supporting Information of this article.

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“…Thus, the delaying effect and unexpected positive effect of icing on primary production have potential implications for the whole ecosystem, at least regarding plant-herbivore interactions (Gauthier et al, 2013; Post & Forchhammer, 2008; Post et al, 2009), carbon fluxes (Schuur et al, 2015) and vegetation-climate feedbacks (Zhang et al, 2020). For instance, the late summer/autumn season is when arctic and temperate large herbivores accumulate body fat, essential for surviving the following winter (Hurley et al, 2014; Loe et al, 2021). Tundra icing may thus have counteracting effects for the herbivores, limiting food availability over the winter leading to starvation, but also increasing the food quantity available in late summer.…”

Section: Discussionmentioning

confidence: 99%

Towards rainy high Arctic winters: how ice-encasement impacts tundra plant phenology, productivity and reproduction

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et al. 2021

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The Arctic is the most rapidly warming region on Earth, but our understanding of ecosystem impacts is still poor. For instance, warming occurs more than twice as fast in winter than in summer, yet long-term tundra vegetation studies have almost exclusively focused on effects of the latter. In winter, more frequent extreme warm spells and associated rain-on-snow events can dramatically alter snowpack conditions and even encapsulate the vegetation in basal ice for several months. Such icing effects on plant phenology, productivity and reproduction remain largely unexplored. We performed a novel five-year-long field experiment in which we simulated every winter a rain-on-snow event resulting in ice encasement of the vegetation, and assessed vascular plant responses in each subsequent growing season. We also tested whether these responses could be modified by summer warming (open top chambers). Icing delayed the dominant shrub`s phenology, in particular early leaf development and seed maturation, increased community-level primary production in the second half of the growing season, but also reduced flower production. These delays and allocation trade-offs were associated with a delay in sub-surface soil thawing and soil warming in spring/summer, conditions known to influence plant root activity and nutrient availability at high latitudes. Interestingly, summer warming mitigated effects of icing alone and the combined treatment showed advanced phenology, increased primary production across the growing season and reduced the negative effects on reproduction. In general, effect sizes of icing were as large as those observed for experimental summer warming alone. The community-level increase in primary production following icing is in sharp contrast with the recently proposed arctic browning effect of extreme winter warm spells in evergreen shrub-dominated tundra communities. Yet, the negative effect on reproductive traits can become critical for species viability if these events become chronic. As we are heading towards a rain-dominated Arctic, our findings highlight the need for coordinated monitoring of the effects of warmer and rainier winters across tundra plant communities and growth forms across the Arctic.

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The neglected season: Warmer autumns counteract harsher winters and promote population growth in Arctic reindeer

Cited by 39 publications

References 66 publications

Snowier winters extend autumn availability of high‐quality forage for caribou in Arctic Alaska

Snowier winters extend autumn availability of high‐quality forage for caribou in Arctic Alaska

Fat storage influences fasting endurance more than body size in an ungulate

Towards rainy high Arctic winters: how ice-encasement impacts tundra plant phenology, productivity and reproduction

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