Optimization of Predator Avoidance by Salamanders Using Chemical Cues: Diet and Diel Effects

The allocation of time and energy to predator defense is a fundamental problem for animals. Predator avoidance may decrease the risk of injury or mortality, but it may also compromise foraging or reproduction, so potential prey should decide whether to avoid a predator based on predation risk. We show that red-backed salamanders (Plethodon cinereus) discriminate between substrates chemically conditioned by garter snakes (Thamnophis sirtalis) that were fed red-backed salamanders, earthworms, or nothing. At night, individuals avoided only the conspecific treatment, and this response was independent of any individual differences between snakes. During the day when garter snakes are much more active, all treatments were avoided. This avoidance appeared to be influenced by a diel rhythm of responsiveness rather than ambient lighting. Avoidance of prey alarm substances released during predation does not explain all these results, nor can simple avoidance of predator scent. A more complex mechanism is proposed that incorporates predator recognition, predator diet discrimination, and risk assessment. These data suggest that terrestrial salamanders may use chemoreception to identify garter snakes and their diets in order to optimize predator avoidance.