Response of predator-naive newt larvae to food and predator presence

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Abstract
For naive prey, the ability to recognize predators is advantageous at the time of first predator encounter. After predator detection, prey could avoid the risk of being eaten by modifying the patterns of activity and use of habitat. The use of refuges is considered one of the most widespread antipredator tactics. In laboratory experiments, we tested the effects of food (cladocerans, Daphnia sp.) and predator (brown trout, Salmo trutta) presence on larval newt (Triturus helveticus and Triturus alpestris) refuging behaviour, and the effect of refuge use on larval survival. Newt larvae came from lakes without fish and were reared in the laboratory from the egg stage so that they lacked any previous experience with brown trout. Larvae of both species increased refuge use and reduced significantly their emergence rate in the presence of predators. Food had no effect on refuge use or activity. For both species, refuge availability increased larval survival by more than twofold when the predator was present. These results suggest that naive newt larvae are able to detect predators and show an innate antipredator response.