Endemism: Ecological state of being unique to a defined geographic location or habitat

For example, many species of lemur are endemic to the island of Madagascar.

There are two types of endemism - paleoendemism and neoendemism. Paleoendemism means that a species used to live in a large area but now lives only in a smaller area. Neoendemism means that a species has recently appeared which is closely related to the main species or one that has formed following hybridization and is now classified as a separate species. This is a common process in plants especially those which exhibit polyploidy.

The opposite of endemism is cosmopolitan distribution.

Endemic types are most likely to develop on islands because they are isolated. This includes remote island groups, like the Hawaiian Islands, the Galápagos Islands, and Socotra. Endemism can also occur in areas which are separated from other similar areas like the highlands of Ethiopia, or large bodies of water like Lake Baikal.

Endemics can easily become endangered or extinct because of only living in a small area. They are also vulnerable to the actions of man, including the introduction of new organisms. There were millions of both Bermuda petrels and "Bermuda cedars" (actually junipers) in Bermuda when it was settled at the start of the 17th century. By the end of the century, the petrels were thought to be extinct. Cedars, whose numbers were low as a result of centuries of shipbuilding, were nearly made extinct in the 20th Century by the introduction of a parasite. Both petrels and cedars are very rare today, as are other species endemic or native to Bermuda.

Endemic organisms are not the same as indigenous organisms — a species that is indigenous to somewhere may be native to other locations as well. An introduced species, also known as a naturalized or exotic species, is an organism that is not indigenous to a given place or area.

According to the World Wildlife Fund, the following ecoregions have the highest percentage of endemic plants:

• Fynbos in the Cape flower region (South Africa)

• Hawaiian tropical dry forests (United States)
• Hawaiian tropical rainforests (United States)

• Kwongan heathlands (Australia)
• Madagascar dry deciduous forests (Madagascar)
• Madagascar lowland forests (Madagascar)
• New Caledonia dry forests (New Caledonia)
• New Caledonia rain forests (New Caledonia)

• Sierra Madre de Oaxaca pine-oak forests (Mexico)
• Sierra Madre del Sur pine-oak forests (Guatemala)

• Luzon montane rainforests (Philippines)
• Luzon rain forests (Philippines)
• Luzon tropical pine forests (Philippines)
• Mindanao montane rain forests (Philippines)
• Mindanao-Eastern Visayas rain forests (Philippines)
• Palawan rain forests (Philippines)

Some of the principal threats to these special ecosystems are:

• Large scale logging operations
• Slash-and-burn techniques (which are sometimes a part of shifting cultivation)
• Destruction of habital or vegetation leads to endangering of the endemic species