Newt
Newts, as with salamanders in general and other amphibians, serve as bioindicators because of their thin, sensitive skin and evidence of their presence (or absence) can serve as an indicator of the health of the environment. Most species are highly sensitive to subtle changes in the pH level of the streams and lakes where they live. Because their skin is permeable to water, they absorb oxygen and other substances they need through their skin. Scientists study the stability of the amphibian population when studying the water quality of a particular body of water.
Marbled newt
Marbled newts live throughout most of France, and northern Spain west to the top third of Portugal. They have a slight overlap with the pygmy marbled newt ("T. pygmaeus"), which take over southern Spain. Marbled newts are absent from most of the Pyrenees because of dry and unstable conditions. In northern France, the populations are more scattered due to the presence of the great crested newt ("T. cristatus"), with which the marbled newt hybridizes to some extent. The higher-elevation Mediterranean climates are the preferred habitat of marbled newts, and in the overlap, "T. pygmaeus" takes the lower elevations.