Terrestrial versus aquatic foraging in juvenile Alpine newts (Triturus alpestris)

Mathieu DENOËL, Laboratory of Fish and Amphibian Ethology, Behavioural Biology Unit, Department of Environmental Sciences, University of Liège, 22 Quai van Beneden, 4020 Liège, Belgium, e-mail: Mathieu.Denoel@ulg.ac.be

Many species of newts and salamanders forage in both terrestrial and aquatic environments during their life. However, the relative benefits of the two foraging patterns remain unknown because all previous studies have focused on only one habitat. The aim of this study was to find out which foraging tactic is the most successful in terms of energy intake. To this end, I analyzed trophic habits in metamorphosed juveniles in the Alpine newt, Triturus alpestris veluchiensis, inhabiting an alpine lake (Drakolimni) and the surrounding lands (Tymphi Mountains, northern Greece). The diet of the newts reflected the range of prey available in the two habitats, but aquatic newts also foraged on invertebrates that fell on the water surface. The two lifestyles have different energy outcomes. Terrestrial invertebrates provided high energy gains mainly to terrestrial juveniles because of the low number of this prey type in the lake. However, terrestrial juveniles are expected to suffer higher mortality (freezing on land is more probable than in deep waters) and a lower energy intake when air temperature is low, i.e., the main pattern in high-elevation sites, except during mid-summer. Persistence of the aquatic foraging tactics in the population may depend on a trade-off between costs and benefits.

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