PhD Thesis Defense: Katie Florko

The Effects of Trophic Interactions and Climate Change on the Space Use of an Arctic Marine Mesopredator
PhD Thesis Defense by:
Katie Florko

December 11, 2023 at 4:30 pm
Room 200, Graduate Student Centre (6371 Crescent Road)

Habitats are heterogeneous landscapes that vary in resource type, abundance, and availability. Animals are expected to select habitat that maximizes energy acquisition to, in turn, increase fitness. As such, food availability influences animal distribution, and the movement of an animal may reveal information on their foraging patterns and food availability. Additionally, predator avoidance affects animal movement, distribution, and behavior. Understanding these dynamics is increasingly important for species that face anthropogenic-caused ecosystem change. I used satellite-telemetered ringed seals (Pusa hispida) in Hudson Bay as a study species to assess the relative influence of bottom-up and top-down pressures. First, I reviewed common statistical methods for using movement data to understand an animal’s relationship with its habitat and created a practical guide for ecologists. Next, using a dynamic bioclimate envelope model, I modeled the changes in the prey base of ringed seals from 1950 to 2100 and demonstrated a climate-driven regime shift in prey, with a 50% decline in the abundance of the well-distributed, ice-adapted and energy-rich Arctic cod (Boreogadus saida), and an increase in the smaller temperate-associated fish in southern and coastal areas. However, I found that all species declined in mean body size, despite an overall 29% increase in total prey biomass. Then, by linking the modeled prey data from 2006 to 2012 to ringed seal movement, I found that seal movement and foraging behavior relative to prey did not match commonly made assumptions, where I found that seals were foraging less in high prey areas. Finally, I considered daily estimates of ringed seal movement relative to polar bear habitat use and found that there were important interactions between prey diversity and polar bear habitat use, where seal movement, habitat selection, and foraging behavior were influenced by the dynamics between top-down and bottom-up pressures. I found that omitting either prey or predators in the seal models biased the estimates of an area’s importance. My thesis provides insight on the trophic interactions and pressures for an Arctic mesopredator in a changing climate and highlights the importance of considering interspecific interactions when modeling movement.

Committee members

Dr. Chris Harley
Dr. Brian Hunt
Dr. Isla Myers-Smith (University examiner)
Dr. Mary O’Connor (University examiner)
Dr. Dave Rosen
Dr. Yuuki Watanabe (External examiner)
Dr. Jiaying Zhao (Chair)