Optimality of feeding on land versus in water in juvenile Alpine newts (Triturus alpestris veluchiensis)

Most newts experience both terrestrial and aquatic environments during their adult life. A large number of studies explored the feeding habits in the aquatic habitat while very few focused on the terrestrial component and none compared the two systems within a single population. 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 analysed the feeding habits of metamorphosed juveniles in the Alpine newt inhabiting a Greek alpine lake and its surrounding lands. The diet reflected the range of prey available in the two habitats, but invertebrates, which fell on the water surface, were also ingested by aquatic newts. These two lifestyles had different energy outcomes because the highest number of terrestrial invertebrates taken in the terrestrial habitat than in the aquatic one provided higher energy gains to terrestrial juveniles. However, different mortality rates between habitats (highest probability of freezing risk on high-elevated lands than in deep waters) and an expected lower energy intake on land when air temperature is low could explain the persistence of the aquatic foraging tactic in the population.