Population dynamics under climate change ad harvesting: Results from the high Arctic Svalbard reindeer

Abstract

To prevent populations or species extinctions due to anthropogenic global change, we need a better mechanistic understanding of the interplay between intrinsic (e.g. resource competition, demographic structure) and extrinsic (e.g. climate change, exploitation) drivers of population dynamics. In this thesis, I demonstrate how interactive effects of climate change and harvesting can shape wildlife population dynamics in time and space. I adopted an interdisciplinary approach combining theoretical and empirical models with time-series data and genetic samples from the high Arctic Svalbard reindeer. I present empirical evidence of the causal links between midwinter rain-on-snow events and basal ice encapsulating the tundra vegetation. These events have become more frequent under recent climate change and can strongly affect resource availability with multiplicative effects on reindeer survival and fecundity at high population densities. Density-dependent effects of rain-on-snow contributed to large-scale spatial synchrony in population fluctuations. However, local populations showed contrasting trends in abundance, which was attributed to spatial heterogeneity in the effects of climate change. This spatial decoupling of population dynamics in the long-run is expected to improve the sub-species’ resilience to climate change. In contrast, analysis of landscape genetics across Svalbard revealed that the rapid loss of sea ice due to climate change leads to increased genetic isolation and, thereby, higher local extinction risk. Moreover, local and regional extinctions due to historical overexploitation and subsequent reintroduction programs modified the observed genetic structure linked to sea ice connectivity and landscape barriers. However, I provide theoretical and empirical-based evidence for a wide range of life histories, with Svalbard reindeer as a case-study, that sustainable harvesting can mitigate over-compensatory responses to weather-induced resource limitation. Thus, harvesting can be used as a management tool to avoid overabundant populations, thereby increasing population stability and resilience to climate change. In conclusion, the results from this thesis demonstrate how anthropogenic stressors can interact to shape population dynamics and genetics in time and space. Accounting for the interplay between different extrinsic and intrinsic drivers could significantly improve the conservation and management of wildlife populations under climate change and harvesting.