Modelling optimal responses and fitness consequences in a changing Arctic

• Author(s) / Creator(s)

  • Jody R. Reimer
  • Marc Mangel
  • Andrew E. Derocher
  • Mark A. Lewis

• Animals must balance a series of costs and benefits while trying to maximize their fitness.
  For example, an individual may need to choose how much energy to allocate to reproduction
  versus growth, or how much time to spend on vigilance versus foraging. Their decisions depend
  on complex interactions between environmental conditions, behavioural plasticity, reproductive
  biology, and energetic demands. As animals respond to novel environmental conditions
  caused by climate change, the optimal decisions may shift. Stochastic dynamic programming
  provides a flexible modelling framework with which to explore these tradeoffs, but this method
  has not yet been used to study possible changes in optimal tradeoffs caused by climate change.
  We created a stochastic dynamic programming model capturing tradeoff decisions required by
  an individual adult female polar bear (Ursus maritimus), as well as the fitness consequences of
  her decisions. We predicted optimal foraging decisions throughout her lifetime, as well as the
  energetic thresholds below which it is optimal for her to abandon a reproductive attempt. To
  explore the effects of climate change, we shortened the spring feeding period by up to 3 weeks,
  which led to predictions of riskier foraging behaviour and higher reproductive thresholds. The
  resulting changes in fitness may be interpreted as a best-case scenario, where bears adapt instantaneously
  and optimally to new environmental conditions. If the spring feeding period was
  reduced by 1 week, her expected fitness declined by 15%, and if reduced by 3 weeks, expected
  fitness declined by 68%. This demonstrates an effective way to explore a species’ optimal
  response to a changing landscape of costs and benefits and highlights the fact that small annual
  effects can result in large cumulative changes in expected lifetime fitness.

• Date created

  2019-01-01

• Subjects / Keywords

  • Ursus maritimus
  • energetic model
  • polar bear
  • climate change
  • stochastic dynamic programming
  • state dependent model
  • optimality theory
  • marine mammal

• Type of Item

  Article (Draft / Submitted)

• DOI

  https://doi.org/10.7939/r3-nh2z-vb42

• License

  Attribution-NonCommercial 4.0 International