The dynamic interaction between predator and prey drives mesopredator movement and foraging ecology
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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 the seals’ 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.
Significance Statement
Our paper explores how animals balance finding food and avoiding predators. This balancing act is often poorly understood, particularly in Arctic ecosystems, but is necessary for understanding and conserving species. Our results show that interactions between polar bear presence and prey diversity explain the foraging behavior, habitat selection, and activity budgets of ringed seals. Seals constrained their movements to areas with low predation risk, but entered high-risk areas if prey diversity was high. Additionally, our inference on the relationship between ringed seals and their prey would be overlooked if the potential risk of polar bear predation was not included. Our study advances our understanding of the complex dynamics in predator-prey ecology, which is essential to incorporate when identifying critical habitat.
