Interrelated ecological impacts of climate change on an apex predator.

Kristin L Laidre,Markus Dyck,Stephen Atkinson,Nicholas J Lunn,Erik W Born,Harry L Stern,Eric V Regehr,Øystein Wiig

doi:10.1002/eap.2071

Abstract

Climate change has broad ecological implications for species that rely on sensitive habitats. For some top predators, loss of habitat is expected to lead to cascading behavioral, nutritional, and reproductive changes that ultimately accelerate population declines. In the case of the polar bear (Ursus maritimus), declining Arctic sea ice reduces access to prey and lengthens seasonal fasting periods. We used a novel combination of physical capture, biopsy darting, and visual aerial observation data to project reproductive performance for polar bears by linking sea ice loss to changes in habitat use, body condition (i.e., fatness), and cub production. Satellite telemetry data from 43 (1991–1997) and 38 (2009–2015) adult female polar bears in the Baffin Bay subpopulation showed that bears now spend an additional 30 d on land (90 d in total) in the 2000s compared to the 1990s, a change closely correlated with changes in spring sea ice breakup and fall sea ice formation. Body condition declined for all sex, age, and reproductive classes and was positively correlated with sea ice availability in the current and previous year. Furthermore, cub litter size was positively correlated with maternal condition and spring breakup date (i.e., later breakup leading to larger litters), and negatively correlated with the duration of the ice‐free period (i.e., longer ice‐free periods leading to smaller litters). Based on these relationships, we projected reproductive performance three polar bear generations into the future (approximately 35 yr). Results indicate that two‐cub litters, previously the norm, could largely disappear from Baffin Bay as sea ice loss continues. Our findings demonstrate how concurrent analysis of multiple data types collected over long periods from polar bears can provide a mechanistic understanding of the ecological implications of climate change. This information is needed for long‐term conservation planning, which includes quantitative harvest risk assessments that incorporate estimated or assumed trends in future environmental carrying capacity.

Highlights

Progressive changes in the abiotic environment are expected to result in profound ecological disruptions for Arctic fauna, sea-ice-dependent species (Post et al 2009, Laidre et al 2015a, Reimer et al 2019)
Satellite telemetry data from 43 (1991–1997) and 38 (2009–2015) adult female polar bears in the Baffin Bay subpopulation showed that bears spend an additional 30 d on land (90 d in total) in the 2000s compared to the 1990s, a change closely correlated with changes in spring sea ice breakup and fall sea ice formation
Sea ice data indicate that the spatial pattern of melt in Baffin Bay has not changed over the last few decades, the timing of that melt has shifted earlier in the season in the 2000s compared to the 1980s and 1990s (Fig. 2)

Summary

Introduction

Progressive changes in the abiotic environment are expected to result in profound ecological disruptions for Arctic fauna, sea-ice-dependent species (Post et al 2009, Laidre et al 2015a, Reimer et al 2019). Polar bears depend on sea ice for most aspects of their life history and are distributed throughout ice-covered areas of the circumpolar Arctic in 19 subpopulations (PBSG 2018). They occur in highest densities on annual ice over the continental shelf and within the channels of archipelagos (Laidre et al 2015a).

Methods

Results

Discussion

Conclusion