The Neotropical realm is one of the eight biogeographic realms constituting Earth's land surface. Physically, it includes the tropical terrestrial ecoregions of the Americas and the entire South American temperate zone. Definition In biogeography, the Neotropic or Neotropical realm is one of the eight terrestrial realms. This realm includes South America, Central America, the Caribbean islands, and southern North America. In Mexico, the Yucatán Peninsula and southern lowlands, and most of the east and west coastlines, including the southern tip of the Baja California Peninsula are Neotropical. In the United States southern Florida and coastal Central Florida are considered Neotropical. The realm also includes temperate southern South America. In contrast, the Neotropical Floristic Kingdom excludes southernmost South America, which instead is placed in the Antarctic kingdom. The Neotropic is delimited by similarities in fauna or flora. Its fauna and flora are distinct from the Nearctic realm (which includes most of North America) because of the long separation of the two continents. The formation of the Isthmus of Panama joined the two continents two to three million years ago, precipitating the Great American Interchange, an important biogeographical event. The Neotropic includes more tropical rainforest (tropical and subtropical moist broadleaf forests) than any other realm, extending from southern Mexico through Central America and northern South America to southern Brazil, including the vast Amazon rainforest. These rainforest ecoregions are one of the most important reserves of biodiversity on Earth. These rainforests are also home to a diverse array of indigenous peoples, who to varying degrees persist in their autonomous and traditional cultures and subsistence within this environment. The number of these peoples who are as yet relatively untouched by external influences continues to decline significantly, however, along with the near-exponential expansion of urbanization, roads, pastoralism and forest industries which encroach on their customary lands and environment. Nevertheless, amidst these declining circumstances this vast "reservoir" of human diversity continues to survive, albeit much depleted. In South America alone, some 350–400 indigenous languages and dialects are still living (down from an estimated 1,500 at the time of first European contact), in about 37 distinct language families and a further number of unclassified and isolate languages. Many of these languages and their cultures are also endangered. Accordingly, conservation in the Neotropical realm is a hot political concern, and raises many arguments about development versus indigenous versus ecological rights and access to or ownership of natural resources.