Increasing humic acid concentration alters the intensity and the diel response of newts to predator olfactory cues

Predation risk affects the behaviour of prey species, which often reduce their activity when predator cues are sensed. The sensory environment influences how prey assess this risk. In aquatic species, medium colour largely depends on dissolved organic carbon, which stains water and impairs vision. In darker media, the lower light level may influence the way individuals express antipredator behaviours throughout the day. However, predictions about how prey should respond are ambiguous. We tested the influence of predation risk (fish olfactory cue) and water colour on the diel activity pattern of the newt Lissotriton vulgaris . Predation risk strongly attenuated activity. The effect of water colour was more complex. Newts reduced their activity in the presence of fish cues. This response occurred earlier in the dark water group than in the control group. Therefore, the interaction between predation risk and water colour was time dependent. Newts may anticipate the shift in the activity of the predator, whose peak activity is expected to occur earlier in darker water too. Our finding highlights the importance of considering the prey's capacity to finely assess variation in predation risk and tune their diel activity to the visual environment. It also emphasizes the need to address this issue not only from the predator's perspective but also from the prey's perspective, to assess the consequences of current changes in sensory environments such as water browning in boreal freshwaters.