Risk of Predation, Variation in Dissolved Oxygen, and their Impact upon Habitat Selection Decisions by Fathead Minnow

Recent laboratory experiments suggest that for some species, an inverse relationship exists between body size and tolerance to hypoxic environments. Since most predator–prey relationships that involve fish require predators to be significantly larger than their prey, it is possible that the smaller prey may exploit their greater tolerance to hypoxic environments and seek such environments as a refuge from their predators. We conducted experiments that provided individually identified prey (fathead minnowPimephales promelas) with three environments that varied in the level of dissolved oxygen. The environments also contained a single live predator (yellow perchPerca flavescens), thus requiring the fathead minnow to make habitat selection decisions involving the risk of predation. By using individuals whose movements could be tracked with passive integrated transponder tags, we demonstrated that initially the prey preferentially occupied locations with lower dissolved oxygen and that such locations successfully excluded the predator. Through time, the predator became capable of using these environments, diminishing the effectiveness of low dissolved oxygen as a refuge against predators. We discuss potential mechanisms for our results and discuss environmental characteristics that would generate physiological predation refuges.