Effects of multiple stressors on the behavior of fish in the presence and absence of a predator.

Abstract

Temperature and oxygen concentration can alter the behavior of animals. While often studied in isolation, these factors frequently co-occur. Together they may have nonadditive effects. The effect of abiotic stressors may also change in the presence of biotic stressors, like predators, due to altered costs and benefits of behaviors. Additionally, species may balance the demands of co-occurring stressors differently depending on their unique needs. Here, we investigated the effects of acute exposures to elevated temperature (16 °C versus 12 °C) and decreased dissolved oxygen (30% versus 100% DO) on the social behavior and activity of two co-occurring freshwater fish (common minnow, Phoxinus phoxinus, and three-spined stickleback, Gasterosteus aculeatus) before and after a simulated predator attack. Prior to the release of the model predator, the effect of one stressor was dependent on the other stressor in minnows. Evidence suggested that minnows were more social in warmer waters, but only in hypoxic conditions, and were less active under hypoxia, but only in warm water. Sticklebacks were more active in warm water at both oxygen concentrations. Following predator release, there were no differences in social behavior, likely because of overall reductions in activity. Our study highlights the need to consider stressor combinations. Minnows appeared to compensate for one abiotic stressor such that effects were only apparent when the stressors were experienced together. However, the arrival of the "predator" masked differences between the treatment groups. Different responses between the species suggest that studies in species interactions are needed to understand community level impacts of multiple stressors.