Interrelated ecological impacts of climate change on an apex predator

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 days on land (90 days 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
years). 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.