Responses of Arctic Caribou (Rangifer tarandus) to Changing Climate Conditions

• Author / Creator

  Mallory, Conor

• The ability of species to adapt to the shifting environmental conditions associated with climate change will be a key determinant of their persistence in the coming decades. This is a challenge already faced by species in the Arctic, where rapid environmental change is well underway. Caribou and reindeer (Rangifer tarandus) play a key role in Arctic ecosystems and provide irreplaceable socioeconomic value to many northern peoples. Recent decades have seen declines in many Rangifer populations, and there is strong concern that climate change is threatening the viability of this iconic Arctic species. Here, I investigated several ways through which climate and climate change either affect or are predicted to affect caribou in the Arctic.
  First, I reviewed the existing literature to provide a broad synthesis of the environmental factors that limit caribou and reindeer populations and how these might be affected by a warming climate. My review suggested that the response of Rangifer populations to climate change is, and will continue to be, varied in large part to their broad circumpolar distribution. Next, I investigated the relationships between broad climate patterns, summer-range quality, and population dynamics in three barren-ground caribou herds in northern Canada. Large-scale climate oscillations might contribute to the observed dramatic fluctuations and regional synchrony in Rangifer abundance, and I tested this hypothesis using long-term barren-ground caribou abundance and physical condition datasets. I found that positive intensities of the Arctic Oscillation (AO) in the summer were associated with warmer temperatures, improved growing conditions for vegetation, and better body condition of caribou. Over this same period, the body condition of female caribou was positively related to fecundity, and population trajectories of caribou herds followed the direction of the AO. These findings suggest that broad climate patterns can influence barren-ground caribou population dynamics through effects on summer-range quality, and that caribou might benefit from increased plant productivity during warmer summers associated with climate change.
  However, the effects of climate change are complex and do not occur in isolation. For example, phenological shifts are occurring in many ecosystems around the world. Failure to adjust migratory and reproductive timing to keep pace with the earlier onset of spring has led to negative demographic effects for populations of species across a variety of taxa. I investigated the response of barren-ground caribou in the Qamanirjuaq herd to changing spring phenology from 2004 to 2016, and found that despite the advancing onset of spring, there was no evidence for the development of a trophic mismatch because the advancing green-up was outpaced by earlier migration and calving by caribou. Changing snow cover on the late winter and migratory ranges was the most-supported driver of advancing migratory behaviour. I next explored the effect of snow conditions on barren-ground caribou movement during spring migration and used a mechanistic movement model, integrated step-selection analysis, to estimate barren-ground caribou habitat selection across 194 individual spring migrations. I found that warmer mean spring temperatures leading to the earlier onset of spring snow melt negatively influenced caribou movement, and caribou travelled slower in years with highly variable melting and patchy spring snow conditions which led to longer time spent in migration.
  Lastly, I used least-cost path analysis and circuit theory to model the effects of sea-ice loss on habitat connectivity for Peary caribou (R. t. pearyi), a subspecies that is widely dispersed across the islands of the Canadian Arctic Archipelago and relies on sea ice to move seasonally between island habitats. My results highlighted the critical role that some islands play in facilitating connectivity between Peary caribou populations, and that without rigorous greenhouse gas emission reductions my projections indicated that by 2100 all connectivity between the more southern Peary caribou populations will be lost for important spring and early-winter movement periods. Although mitigating climate change at regional levels is challenging due to its global causes, climate change impacts to species might be moderated through conservation areas that allow species to adapt or adjust to changing conditions. My work used data-driven approaches to identify important areas for both the Qamanirjuaq migration and Peary caribou connectivity, and by permitting caribou to continue to use these areas undisturbed we might provide them with a better opportunity to adjust to rapid environmental change.

• Subjects / Keywords

  • Arctic
  • migration
  • caribou
  • climate change

• Graduation date

  Fall 2019

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/r3-a8qn-s692

• License

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