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.
Italian crested newt
Temperature in amphibians and reptiles directly affects metabolism in an exponential manner, and among ectotherms, temperature is one of the most important factors, acting directly upon metabolism. Since the newt is a poikilotherm, the purpose of this increase in metabolism is not to generate heat to regulate their internal temperature, but to counteract the depressive effect on standard metabolism that low atmospheric temperatures produce. For example, there is a direct correlation between the activity of certain muscle metabolic enzymes and the preferred body temperature of Eastern red spotted newts.