Seasonal effects of Pacific-based climate on recruitment in a predator-limited large herbivore

Authors

  • Troy M. Hegel,

    Corresponding author
    1. Department of Biology, Center for Ecological and Evolutionary Synthesis (CEES), University of Oslo, P.O. Box 1066, Blindern N-0316, Oslo, Norway
    2. Institute of Arctic Biology, University of Alaska Fairbanks, P.O. Box 757000, Fairbanks, AK 99775, USA
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  • Atle Mysterud,

    1. Department of Biology, Center for Ecological and Evolutionary Synthesis (CEES), University of Oslo, P.O. Box 1066, Blindern N-0316, Oslo, Norway
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  • Torbjørn Ergon,

    1. Department of Biology, Center for Ecological and Evolutionary Synthesis (CEES), University of Oslo, P.O. Box 1066, Blindern N-0316, Oslo, Norway
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  • Leif Egil Loe,

    1. Department of Biology, Center for Ecological and Evolutionary Synthesis (CEES), University of Oslo, P.O. Box 1066, Blindern N-0316, Oslo, Norway
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  • Falk Huettmann,

    1. Institute of Arctic Biology, University of Alaska Fairbanks, P.O. Box 757000, Fairbanks, AK 99775, USA
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  • Nils Chr. Stenseth

    1. Department of Biology, Center for Ecological and Evolutionary Synthesis (CEES), University of Oslo, P.O. Box 1066, Blindern N-0316, Oslo, Norway
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  • †Present address: Environment Yukon, P.O. Box 2703, Whitehorse, YT Y1A 2C6, Canada

*Correspondence author. E-mail: Troy.Hegel@gov.yk.ca

Summary

1. Climate is an important factor influencing the population dynamics of large herbivores operating directly on individuals or through its effect on forage characteristics. However, the seasonal effect of climate may differ between forage- and predator-limited populations because of a climatic influence on predation rates. The influence of climate on predator-limited large herbivores is less well known than on forage-limited populations. Further, the effect of Pacific-based climate on large herbivore populations has been rarely assessed.

2. We investigated the effect of the Pacific Decadal Oscillation (PDO), across different seasons, on recruitment in 10 populations (herds) of mountain-dwelling caribou Rangifer tarandus caribou L. in the Yukon Territory, Canada. These low-density populations occur in highly seasonal environments and are considered predator-limited with high neonatal calf mortality. Hence, in most years females do not spend resources through lactational support during the summer and resource intake is devoted to self-maintenance. We predicted that climate affecting environmental conditions at calving would have a strong effect on recruitment via its influence on predation rates. We also predicted that climatic conditions prior to conception could have an effect on recruitment through its influence on female fecundity. We modelled recruitment (= 165) by seasonal PDO values using generalized linear mixed-effects models with herd-varying coefficients.

3. We found that recruitment variability was best explained by variation in winter climate (β = 0·110, SE = 0·007) prior to birth (in utero) and May climate (β = 0·013, SE = 0·006) at calving. There was little support for a pre-conception climate effect influencing female body condition and hence fecundity. These results confirm that recruitment in these populations is limited by predation and that forage-limitation is not a significant factor in their population dynamics. There was considerable variability in herd-specific relationships between the PDO and recruitment. Incorporating herd-specific characteristics, such as variable predator densities or terrain characteristics within a herd range, may shed greater light on the complex relationship between climate and ungulate population dynamics.

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