Public Defence: Ashlee Jean Mikkelsen

Ashlee Jean Mikkelsen is defending her thesis for the degree philosophiae doctor (PhD) at the University of South-Eastern Norway.

The doctoral work has been carried out at the Faculty of Technology, Natural Sciences and Maritime Sciences in the program Ecology.

Everyone is welcome to follow the trial lecture and the public defence.

Read the thesis here: USN Open Archive: The effects of diet and metabolism on the life history of an omnivorous carnivore

Summary

Despite often being portrayed as ferocious predators, brown bears (Ursus arctos) in Scandinavia had annual diets with low proportions of animal-derived foods (~12%), even though these foods appear to be plentiful on the landscape.

Across 25 years, brown bear diet did not respond to changes in moose populations, rather it seems to be driven by bilberry (Vacinium myrtillus) production. Populations of brown bears that have diets low in animal-derived foods tend to be smaller than populations with meat-heavy diets and this is assumed to be a result of either energy or protein deficiencies that limit growth and decrease fitness in those animals.

However, brown bears in Scandinavia invested more in their own growth and self-maintenance rather than in their offspring, indicating that females in this population did not have to sacrifice growth to fuel reproduction. It is likely this population doesn’t suffer fitness cost from their low-protein diet, rather they have adapted and thrive in an ecosystem that can support them, even with a diet low in animal-derived foods. This adds to a growing body of evidence that carnivory in many species has been over-emphasized.

Further, when we compared our observed brown bear diets to estimated diets based on prevailing ecological theories, we found that none of the ecological theories was sufficient in describing brown bear diet and ecological function.

We arrived at these results and conclusions from five studies in which we used molecular markers of diet and metabolic demands (stable isotopes and cortisol, respectively) measured from brown bear hair with physiological indicators of physiological health (body condition) and life-history information (reproductive status, age, sex, body size and mass) collected in south-central Sweden over 25 years. This data comes from individually marked individuals that were followed throughout their lifetime and captured multiple times.

We used several statistical modelling techniques to quantitatively determine correlations between diet, body condition, metabolic demands, life-history, and the environment. We placed our findings in the context of broad ecological theories to improve our understanding of how animals allocate energy in a world of limited resources, given competing metabolic demands and decades of landscape changes.