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Endemism is the ecological state of a species being native to a single defined geographic location, such as an island, region, state or other defined zone, or habitat type; organisms that are indigenous to a place are not endemic to it if they are also found elsewhere. For example, the orange-breasted sunbird is exclusively found in the fynbos vegetation zone of southwestern South Africa and the glacier bear is a subspecies endemic to Southeast Alaska. The extreme opposite of an endemic species is one with a cosmopolitan distribution, having a global or widespread range. An alternative term for a species that is endemic is precinctive, which applies to species (and other taxonomic levels) that are restricted to a defined geographical area.
The word endemic is from New Latin endēmicus, from Greek ενδήμος, endēmos, "native". Endēmos is formed of en meaning "in", and dēmos meaning "the people". The term "precinctive" has been suggested by some scientists as the equivalent of "endemism",[a] and was first used in botany by MacCaughey in 1917. Precinction was perhaps first used by Frank and McCoy. Precinctive seems to have been coined by David Sharp when describing the Hawaiian fauna in 1900: "I use the word precinctive in the sense of 'confined to the area under discussion' ... 'precinctive forms' means those forms that are confined to the area specified." This definition (and endemism in general) excludes artificial confinement of examples by humans in far-off botanical gardens or zoological parks.
There are two subcategories of endemism: paleoendemism and neoendemism. Paleoendemism refers to species that were formerly widespread but are now restricted to a smaller area. Neoendemism refers to species that have recently arisen, such as through divergence and reproductive isolation or through hybridization and polyploidy in plants, and have yet to disperse beyond a limited range. Charles Darwin's study of neoendemic species in locations like the Galápagos Islands helped form his ideas of evolution by natural selection.
Although the specific drivers of endemism are unclear, physical, climatic, and biological factors can contribute to endemism. Endemic species are especially likely to develop on geographically and biologically isolated areas such as islands and remote island groups, including Hawaii, the Galápagos Islands and Socotra, because of the potential for isolation and therefore evolution through allopatric speciation. Darwin's finches in the Galápagos archipelago and Hydrangea hirta, endemic to Japan, are examples of species endemic to islands. Similarly, isolated mountainous regions like the highlands of Ethiopia, or large bodies of water far from other lakes, like Lake Baikal, can also have high rates of endemism.
The stability of a region's climate and habitat through time may also contribute to high rates of endemism (especially paleoendemism), acting as refuges for species during times of climate change like the Ice Ages. These changes may have caused species to repeatedly restrict their ranges into these refuges, leading to regions with many small-ranged species.
Threats to regions with high endemismEdit
Endemic species can easily become endangered or extinct if their already restricted habitat changes, particularly—but not only—due to human actions, including the introduction of new species. The dodo, a flightless bird species endemic to Mauritius in the Indian Ocean, is a famous example of the vulnerability of endemic species to habitat alteration: the dodo became extinct within decades of the first permanent human settlement on the island in 1638. A dodo was last seen in 1688, ninety years after the birds' first recorded description in 1598.
There were millions of both Bermuda petrels and Bermuda cedars in Bermuda when it was settled at the start of the seventeenth century. By the end of the century, the petrels were thought extinct. Cedars, already ravaged by centuries of shipbuilding, were driven nearly to extinction in the twentieth century by the introduction of a parasite. Bermuda petrels and cedars are now rare, as are other species endemic to Bermuda.
Principal causes of habitat degradation and loss in ecosystems with high rates of endemism include agriculture, urban growth, surface mining, mineral extraction, logging operations and slash-and-burn agriculture.
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