Figure 2. Annual variation in hair stable isotope values for
nitrogen (δ 15N, A) and carbon
(δ 13C, B) for a population of brown bears in
Sweden 199–2020. Box plots depict the annual means, quantiles, and
outliers, while colored points depict the observed values by demographic
class.
There was strong support in the data that δ 13C
values were lower in years with greater bilberry production
(\({\widehat{\beta}}_{\left(\ln\left(\text{Bilberry}\right)\right)}=-0.21,\ 95\%\ CI=-0.30\ to-0.12\))
and greater numbers of observed moose calves
(\({\widehat{\beta}}_{\left(\text{MooseCalves}\right)}=\ -0.25,\ 95\%\ CI=-0.35\ to-0.14\)).
animal foods (i.e., moose and ants) had the highestδ 13C values, crowberry and lingonberry had
median δ 13C values, and bilberry had the lowestδ 13C value. In years with high bilberry
production, brown bear δ 13C values were more
similar to bilberry, which should indicate a diet higher in bilberry,
even when moose calf numbers were high.