Diet composition of the Italian crested newt (Triturus carnifex) in structurally different artificial ponds based on stomach contents and stable isotope analyses

In order to evaluate the effects of ecological disturbances, such as climate change, human-induced habitat modification, or species introduction, and in order to adopt appropriate management policies for their conservation, knowledge of the trophic ecology of protected or threatened species is crucial. The Italian crested newt, Triturus carnifex (Laurenti, 1768), is listed in annexes II and IV of the European Habitats Directive. For this species, changes in water quality and habitat loss represent major threats, potentially impairing its breeding and feeding activities. Artificial aquatic habitats, such as cattle-drinking pools, represent valuable refuges and suitable breeding sites for T. carnifex. The aim of this study was to determine the food niche of the Italian crested newt in these habitats, evaluating its prey selection strategy in relation to a range of environmental conditions and differing availability of resources. Stomach contents (indicative of short-term diet) and δ13C and δ15N signatures of tails (indicative of medium-term diet) of adult newts from three artificial ponds in central Italy, where traditional silvo-pastoral activities are still important, were determined. Potential prey were also sampled and processed for stable isotope analysis. Triturus carnifex, similar to other newt species, is an opportunistic predator, feeding on a wide variety of prey that includes terrestrial and aquatic macroinvertebrates. In particular, the opportunistic use of temporally available small zooplankton was identified from stomach contents analysis. Conversely, stable isotope analysis highlighted the consumption of larger, soft-bodied prey that the stomach-contents-based approach underestimated. These included terrestrial oligochaetes, which turned out to be the most important and energy-rich food source in the medium term. These results emphasize the usefulness of combined approaches for studying the trophic ecology of salamanders and also highlight the importance of the integrated management of aquatic breeding habitats and neighbouring terrestrial habitats, as sources of food, for newt conservation.