Contrasting effects of summer and winter warming on body mass explain population dynamics in a food-limited Arctic herbivore

Steve D Albon, R Justin Irvine, Odd Halvorsen, Rolf Langvatn, Leif E Loe, Erik Ropstad, Vebjørn Veiberg, René van der Wal, Eirin M Bjørkvoll, Elizabeth I Duff, Brage Bremset Hansen, Aline M Lee, Torkild Tveraa, Audun Stien

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Abstract

The cumulative effects of climate warming on herbivore vital rates and population dynamics are hard to predict, given that the expected effects differ between seasons. In the Arctic, warmer summers enhance plant growth which should lead to heavier and more fertile individuals in the autumn. Conversely, warm spells in winter with rainfall (rain-on-snow) can cause 'icing', restricting access to forage, resulting in starvation, lower survival and fecundity. Since body condition is a 'barometer' of energy demands relative to energy intake, we explored the causes and consequences of variation in body mass of wild female Svalbard reindeer (Rangifer tarandus platyrhynchus) from 1994-2015, a period of marked climate warming. Late winter (April) body mass explained 88% of the between-year variation in population growth rate, because it strongly influenced reproductive loss, and hence subsequent fecundity (92%), as well as survival (94%) and recruitment (93%). Autumn (October) body mass affected ovulation rates but did not affect fecundity. April body mass showed no long-term trend (Coefficient of variation, CV = 8.8%) but was higher following warm autumn (October) weather, reflecting delays in winter onset, but most strongly, and negatively, related to 'rain-on-snow' events. October body mass (CV =2.5%) increased over the study due to higher plant productivity in the increasingly warm summers. Density-dependent mass change suggested competition for resources in both winter and summer but was less pronounced in recent years, despite an increasing population size. While continued climate warming is expected to increase the carrying capacity of the high Arctic tundra, it is also likely to cause more frequent icing-events. Our analyses suggest that these contrasting effects may cause larger seasonal fluctuations in body mass and vital rates. Overall our findings provide an important 'missing' mechanistic link in the current understanding of the population biology of a keystone species in a rapidly warming Arctic. This article is protected by copyright. All rights reserved.

Original languageEnglish
Pages (from-to)1374–1389
Number of pages16
JournalGlobal Change Biology
Volume23
Issue number4
Early online date6 Aug 2016
DOIs
Publication statusPublished - 1 Apr 2017

Keywords

  • Climate change
  • density dependence
  • extreme events
  • icing
  • nutrition
  • primary production
  • Rangifer
  • Reindeer
  • Svalbard
  • weather

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    Albon, S. D., Irvine, R. J., Halvorsen, O., Langvatn, R., Loe, L. E., Ropstad, E., Veiberg, V., van der Wal, R., Bjørkvoll, E. M., Duff, E. I., Hansen, B. B., Lee, A. M., Tveraa, T., & Stien, A. (2017). Contrasting effects of summer and winter warming on body mass explain population dynamics in a food-limited Arctic herbivore. Global Change Biology, 23(4), 1374–1389. https://doi.org/10.1111/gcb.13435