UC Santa Cruz

Migratory animals are ecologically and economically important and are especially vulnerable to predation. Predators affect migratory prey through both consumption and changes to prey behavior scaling up to affect populations to communities. The balance between consumptive and behavioral predator effects are shaped by risk-reward tradeoffs and ecological constraints. The unique biology of migratory animals results in tradeoffs and constraints involving energetic-demands and optimal timing of migration and traversing heterogeneous and unfamiliar habitats. The goal of my dissertation is to examine how predators affect migrating prey behavior, ecology, and evolution. I used diverse approaches to understand the intersection of predation and migration from fine-scale behavioral decisions up to large-scale patterns among populations and species. In chapter 1, I developed a conceptual framework to predict how migrating prey perceive and respond to predation risk—a direct extension of classic economic escape theory. In chapters 1 and 2, I tested this theory empirically using behavioral assays where I timed juvenile salmon swimming downstream with and without predator cues. In two experiments, juvenile salmon changed behavior (speed) in response to predator cues, but the pattern of response was context-dependent on previous predator experience and habitat. In chapter 1, wild salmon with more previous predator experience reacted more strongly to predation risk than hatchery salmon. In chapter 2, salmon responded more strongly to predation risk in the shade compared to direct sun and varied their escape strategy—slowing down in the shade and speeding up in the sun. In chapter 3, I conducted a global synthesis across taxa that examines how predators shape animal migrations from behavior to population dynamics to life history evolution. It further explores how humans are disrupting these predator-prey interactions and provides suggestions on how to conserve healthy predation landscapes. Using diverse approaches, from mechanisms to population consequences to ecosystem effects, this work increases our general ecological understanding of predator effects on migratory prey and informs efforts to conserve threatened migratory prey.