Evolutionary responses to a changing climate: Implications for reindeer population viability

Authored by Bard-Jorgen Bardsen

Date Published: 2017

DOI: 10.1002/ece3.3119

Sponsors: Norwegian Research Council (NRF)

Platforms: R

Model Documentation: Other Narrative Mathematical description

Model Code URLs: Model code not found

Abstract

If we want to understand how climate change affects long-lived organisms, we must know how individuals allocate resources between current reproduction and survival. This trade-off is affected by expected environmental conditions, but the extent to which density independent (DI) and density dependent (DD) processes interact in shaping individual life histories is less clear. Female reindeer (or caribou: Rangifer tarandus) are a monotocous large herbivore with a circumpolar distribution. Individuals that experience unpredictable and potentially harsh winters typically adopt risk averse strategies where they allocate more resources to building own body reserves during summer and less to reproduction. Such a strategy implies that the females do not reproduce or that they produce fewer or smaller offspring. A risk averse strategy thus results in females with large autumn body reserves, which is known to increase their survival probabilities if the coming winter is harsh. In contrast, females experiencing predictable winters may adopt a more risk prone strategy in which they allocate more resources to reproduction as they do not need as many resources to buffer potentially adverse winter conditions. This study uses a seasonal state-dependent model showing that DD and DI processes interact to affect the evolution of reproductive strategies and population dynamics for reindeer. The model was run across a wide range of different winter climatic scenarios: One set of simulations where the average and variability of the environment was manipulated and one set where the frequency of good and poor winters increased. Both reproductive allocation and population dynamics of reindeer were affected by a combination of DI and DD processes even though they were confounded (harsh climates resulted in lowered density). Individual strategies responded, in line with a risk sensitive reproductive allocation, to climatic conditions and in a similar fashion across the two climatic manipulations.

Tags

Dynamics Ungulates Convergence fitness Costs Life-history Density-dependence Moose alces-alces Fluctuating environments Dynamic optimization Population dynamics Agent- Individual-based model (abm Ibm) Arctic Subarctic Density dependent selection Environmental unpredictability Pastoral livelihood Sensitive reproductive allocation Soay sheep Dependent selection