The dynamics of habitat choice: low-oxygen areas can be safer

Posted on June 1, 2016

Animals should spend more time in habitats where their predation risk is low and their foraging rewards are high. However, habitat use is also affected by the degree of physiological stress imposed by environmental factors such as oxygen, pH, salinity and temperature. Because prey are under greater selective pressure from being eaten than predators are from missing a meal, prey should be willing to accept a higher cost in terms of stress in order to reduce their predation risk. To test this prediction, a field experiment was conducted in Blind Channel, a stream connected to Lake Manitoba, Canada. Barrier nets were used to create a series of artificial bays (each 10m × 10m x 1m deep) that fish could enter from the channel. Locally-caught predatory fish (perch Perca flavescens, drum Aplodinotus grunniens and bullheads Ameiurus melas and A. nebulosus) were implanted with passive integrated transponder (PIT) tags and released into the channel . PIT tag antennae were placed in each bay to monitor bay use by predators. Minnow traps set near the surface and food plates placed close to the bottom were used to monitor the use of habitats by a prey species (fathead minnow, Pimephales promelas). The feeding plates were made by sticking a mixture of trout crumble and gravel to plastic bases. A low oxygen (2–3mg/litre DO) treatment was created by adding bagged grass clippings to some of the bays. Data analysis showed that oxygen depletion significantly reduced the time that all four predator species spent in the experimental bays. In contrast, in the oxygen-depleted bays, catches of the prey species were higher and more food was removed from the feeding plates, which suggested that prey perceived the low-oxygen bays as safer habitats. Therefore, oxygen-depleted areas may be important predation refuges for small fish, including the juveniles of large-bodied species.

Reference: Hedges, K.J. & Abrahams, M.V. 2015. Hypoxic refuges, predator–prey interactions and habitat selection by fishes. Journal of Fish Biology 86, 288–303.