Leopard frogs, also called meadow frogs, are the archetypal "grass frogs" of North America, a collection of about 14 species within the true frog genus Rana. They are generally very similar, green with prominent black spotting (though actually more like that of a cheetah than that of a leopard). They can be told apart by their distribution and certain rather subtle ecological, behavioral, morphological and genetic traits. Their range extends throughout temperate and subtropical North America to northern Mexico, with some species found even further south. Once abundant in North America, their population has declined in recent years because of pollution and deforestation. What is the main idea ? Answer and explain in 2 - 3 sentences.