Eigil Reimers; Body composition, mortality and population regulation of Svalbard reindeer

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doi:10.7557/2.2.2.417

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“…We quantified the effects of environmental, behavioural and physiological factors on variation in heart rate of Svalbard reindeer (Rangifer tarandus platyrhynchus)-a keystone species in the High Arctic with strong seasonal changes in nutrition and metabolic activity. Inhabiting a predator-free environment, they forage for up to 70% of their time in summer to meet the energetic demands of reproduction [43] and accumulate large fat reserves critical for survival during the long, cold winter [44]. Svalbard reindeer exhibit the largest seasonal amplitude in daily resting heart rate recorded in any ungulate [34] and downregulate metabolic rate during winter even when fed ad libitum in captivity [45].…”

Section: Introductionmentioning

confidence: 99%

Determinants of heart rate in Svalbard reindeer reveal mechanisms of seasonal energy management

Trondrud

Pigeon

Albon

et al. 2021

Phil. Trans. R. Soc. B

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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)’.

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Section: Introductionmentioning

confidence: 99%

Determinants of heart rate in Svalbard reindeer reveal mechanisms of seasonal energy management

Trondrud

Pigeon

Albon

et al. 2021

Phil. Trans. R. Soc. B

View full text Add to dashboard Cite

show abstract

“…Variation in body size and mass between cohorts can be up to 20%, as a result of early life conditions (Douhard et al, 2016). Furthermore, individual body mass varies greatly throughout the year with rapid growth and fattening during the short Arctic summer, and a depletion of up to 50% of body mass by the end of winter (Reimers & Ringberg, 1982).…”

Section: Introductionmentioning

confidence: 99%

“…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). Therefore, body composition may be more relevant for determining FE than body mass itself.…”

Section: Introductionmentioning

confidence: 99%

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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Eigil Reimers; Body composition, mortality and population regulation of Svalbard reindeer

Abstract: Body composition, mortality and population regulation of Svalbard reindeer. Vekst og kondisjon, dødelighet og bestandsregulering av Svalbard-rein. Forsvart for Den filosofiske doktorgrad ved Oslo Universitet 19. november 1982.

Cited by 2 publications

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Determinants of heart rate in Svalbard reindeer reveal mechanisms of seasonal energy management

Determinants of heart rate in Svalbard reindeer reveal mechanisms of seasonal energy management

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

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