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.
Cactoblastis cactorum
In South America, "Cactoblastis cactorum" has many natural predators, including ants and New World monkeys. Ants, the moths' main predators, consume its larvae. New World monkeys dig the larvae and pupae out from the flattened leaf-like stems, or "cladodes", of the cacti. The relationship between "Cactoblastis cactorum" and "Opuntia" cactus species is parasitic: the moth feeds on the host cactus. Recent work in South America has identified four genetically-structured ecotypes of "C. cactorum" that infest different hosts and possess different larval morphology. The mechanism driving this isolation and pattern of host-association in the field remains unexplored.