Data from: Juvenile predation overwhelms nutritional effects on female ungulate fat reserves in a high-predation system

Ungulate body fat reserves reflect the nutritional environment, often
serving as a useful indicator of bottom-up resource availability. However,
body fat reserves also integrate energetic costs associated with avoiding
predation risk and reproductive effort, and it is unknown how bottom-up
and top-down factors integrate to affect body fat reserves. We used
generalized mixed-effects models to evaluate how bottom-up, top-down, and
intrinsic factors explained variation in winter ingesta-free body fat
(IFBF) of female elk (Cervus canadensis) near Banff National Park,
Alberta, Canada, from 2015 to 2021. We found two top models were
competitive, with calf survival during the first 3-4 months of life and
female age included in both models. There was more support for bottom-up
forage effects than indirect predation risk effects. Based on model
predictions, females with a calf surviving through the previous summer had
3.6 percentage points (95% CI: 2.4%, 4.9%) lower IFBF the subsequent
winter than females without a surviving calf. Because calf survival during
the first 3-4 months of life is largely driven by predation in this
system, we suggest top-down effects of predation through calf mortality
influenced body fat around 9 times more than bottom-up factors in our
study. Under high predation, variation in body fat levels of female
ungulates across a population may not reflect only bottom-up influences on
body condition, but also differences in predation. Thus, both bottom-up
and top-down factors must be considered when assessing the nutritional
environment.