The dynamic interaction between predator and prey drives mesopredator movement and foraging ecology

Abstract

Prey availability is a fundamental driver of animal distribution, movement, and foraging ecology. The perceived risk of predation also influences these aspects of animal ecology. Our paper explores how animals balance these tradeoffs, which are seldom analyzed together. Such understanding becomes increasingly important as species that face anthropogenic-caused ecosystem change. In the Arctic, there has been substantial research on consequences of sea ice loss, however our understanding of top-down and bottom-up processes is limited. Ringed seals (Pusa hispida) and polar bears (Ursus maritimus), form a strong predator-prey relationship but limited information is available explaining how fear of polar bears affects ringed seal ecology. Using a large tracking dataset from 26 ringed seals with >70,000 dives and >10,000 locations, we explored the influence of top-down (polar bear space use based on >18,000 locations) and bottom-up (modeled fish distribution) processes on the movement, habitat selection, and foraging behavior of this mesopredator. Our results suggest that polar bears spatially restrict seal movements and reduce the amount of time they spend in area-restricted search and at depth, which likely decreases seal foraging success. However, we found tradeoffs between predation risk and foraging, where ringed seals were more likely to be present and dive for a long duration in high-risk areas when prey diversity was high. Prey habitat use models that excluded predators overestimated core space use. These findings illustrate the dynamic tradeoffs that mesopredators are forced to make when balancing the risk of predation and need to forage.