Local extinction
Local extinction, also known as extirpation, is the condition of a species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...

 (or other taxon
|thumb|270px|[[African elephants]] form a widely-accepted taxon, the [[genus]] LoxodontaA taxon is a group of organisms, which a taxonomist adjudges to be a unit. Usually a taxon is given a name and a rank, although neither is a requirement...

) which ceases to exist in the chosen geographic area of study, though it still exists elsewhere. Local extinctions are contrasted with global extinctions.

Local extinctions may be followed by a replacement of the species taken from other locations; wolf reintroduction
Wolf reintroduction
Wolf reintroduction involves the artificial reestablishment of a population of wolves in areas where they have been extirpated. Wolf reintroduction is only considered where large tracts of suitable wilderness still exist and where certain prey species are abundant enough to support a predetermined...

 is an example of this.


Local extinctions mark a change in the ecology
Ecology is the scientific study of the relations that living organisms have with respect to each other and their natural environment. Variables of interest to ecologists include the composition, distribution, amount , number, and changing states of organisms within and among ecosystems...

 of an area.

The area of study chosen may reflect a natural subpopula political, boundaries, or both. The Cetacean Specialist Group of the IUCN has assessed the threat of a local extinction of the Black Sea
Black Sea
The Black Sea is bounded by Europe, Anatolia and the Caucasus and is ultimately connected to the Atlantic Ocean via the Mediterranean and the Aegean seas and various straits. The Bosphorus strait connects it to the Sea of Marmara, and the strait of the Dardanelles connects that sea to the Aegean...

 stock of Harbour Porpoise
Harbour Porpoise
The harbour porpoise is one of six species of porpoise. It is one of the smallest marine mammals. As its name implies, it stays close to coastal areas or river estuaries, and as such, is the most familiar porpoise to whale watchers. This porpoise often ventures up rivers, and has been seen...

 (Phocoena phocoena) which touches six different countries. COSEWIC, by contrast, investigate wildlife only in Canada, so assesses only the risk of a Canadian local extinction even for species which cross into the United States or other countries. Other subpopulations may be naturally divided by political or country boundaries.

Many crocodilian species have experienced localized extinction, particularly the saltwater crocodile
Saltwater Crocodile
The saltwater crocodile, also known as estuarine or Indo-Pacific crocodile, is the largest of all living reptiles...

 (Crocodylus porosus) which has been extirpated from Vietnam, Thailand, Java, and many other areas.

Often a subpopulation of a species will also be a subspecies
Subspecies in biological classification, is either a taxonomic rank subordinate to species, ora taxonomic unit in that rank . A subspecies cannot be recognized in isolation: a species will either be recognized as having no subspecies at all or two or more, never just one...

. For example, the recent disappearance of the Black Rhinoceros
Black Rhinoceros
The Black Rhinoceros or Hook-lipped Rhinoceros , is a species of rhinoceros, native to the eastern and central areas of Africa including Kenya, Tanzania, Cameroon, South Africa, Namibia, Zimbabwe, and Angola...

 (Diceros bicornis) from Cameroon
Cameroon, officially the Republic of Cameroon , is a country in west Central Africa. It is bordered by Nigeria to the west; Chad to the northeast; the Central African Republic to the east; and Equatorial Guinea, Gabon, and the Republic of the Congo to the south. Cameroon's coastline lies on the...

 spells not only the local extinction of rhinoceroses in Cameroon, but also the global extinction of the Western Black Rhinoceros
Western Black Rhinoceros
The Western Black Rhinoceros or West African Black Rhinoceros is an extinct subspecies of the Black Rhino...

 (Diceros bicornis longipes).

In at least one case, scientists have found a local extinction useful for research: In the case of the Bay Checkerspot
Bay Checkerspot
-- 21:10, 1 December 2011 The Bay Checkerspot is a threatened insect subspecies which is native to the U.S. State of . Since the 23911s the population of checkerspots has been in serious decline...

, scientists, including Paul R. Ehrlich
Paul R. Ehrlich
Paul Ralph Ehrlich is an American biologist and educator who is the Bing Professor of Population Studies in the department of Biological Sciences at Stanford University and president of Stanford's Center for Conservation Biology. By training he is an entomologist specializing in Lepidoptera , but...

, chose not to intervene in a local extinction, using it to study the danger to the world population. However, similar studies are not carried out where a global population is at risk.

IUCN subpopulation and stock assessments

While the World Conservation Union
World Conservation Union
The International Union for Conservation of Nature and Natural Resources is an international organization dedicated to finding "pragmatic solutions to our most pressing environment and development challenges." The organization publishes the IUCN Red List, compiling information from a network of...

 (IUCN) mostly only categorizes whole species or subspecies, assessing the global risk of extinction, in some cases it also assesses the risks to stocks and populations, especially to preserve genetic diversity. In all, 119 stocks or subpopulations across 69 species have been assessed by the IUCN in 2006.

Examples of stocks and populations assessed by the IUCN for the threat of local extinction:
  • Marsh Deer
    Marsh Deer
    The Marsh Deer, Blastocerus dichotomus , is the largest deer species from South America reaching a length of and a height of at the rump. It is found in Argentina, Bolivia, Brazil, Uruguay and Paraguay...

     (three subpopulations assessed)
  • Blue Whale
    Blue Whale
    The blue whale is a marine mammal belonging to the suborder of baleen whales . At in length and or more in weight, it is the largest known animal to have ever existed....

    , North Pacific stock and North Atlantic stock
  • Bowhead Whale
    Bowhead Whale
    The bowhead whale is a baleen whale of the right whale family Balaenidae in suborder Mysticeti. A stocky dark-colored whale without a dorsal fin, it can grow to in length. This thick-bodied species can weigh to , second only to the blue whale, although the bowhead's maximum length is less than...

    , Balaena mysticetus (five subpopulations assessed), from Critically Endangered to LR/cd
  • Lake Sturgeon
    Lake sturgeon
    The lake sturgeon is a North American temperate freshwater fish, one of about 20 species of sturgeon. Like other sturgeons, this species is an evolutionarily ancient bottomfeeder with a partly cartilaginous skeleton and skin bearing rows of bony plates...

    , Acipenser fulvescens, Mississippi & Missouri Basins subpopulation assessed as Vulnerable
    Vulnerable species
    On 30 January 2010, the IUCN Red List of Threatened Species identified 9694 Vulnerable species, subspecies and varieties, stocks and sub-populations.-References:...

  • Wild Common carp
    Common carp
    The Common carp is a widespread freshwater fish of eutrophic waters in lakes and large rivers in Europe and Asia. The wild populations are considered vulnerable to extinction, but the species has also been domesticated and introduced into environments worldwide, and is often considered an invasive...

    , Cyprinus carpio (River Danube subpopulation)
  • Black-footed Rock Wallaby Petrogale lateralis (MacDonnell Ranges subpopulation and Western Kimberly subpopulation)

The IUCN also lists countries where assessed species, subspecies or subpopulations are found, and from which countries they have been extirpated or reintroduced.

The IUCN has only three entries for subpopulations which have become extinct the Aral Sea
Aral Sea
The Aral Sea was a lake that lay between Kazakhstan in the north and Karakalpakstan, an autonomous region of Uzbekistan, in the south...

 stock of Ship sturgeon (Acipenser nudiventris); the Adriatic Sea
Adriatic Sea
The Adriatic Sea is a body of water separating the Italian Peninsula from the Balkan peninsula, and the system of the Apennine Mountains from that of the Dinaric Alps and adjacent ranges...

 stock of Beluga
Beluga sturgeon
The beluga or European sturgeon is a species of anadromous fish in the sturgeon family of order Acipenseriformes. It is found primarily in the Caspian and Black Sea basins, and occasionally in the Adriatic Sea...

 (Huso huso); and the Mexican
The United Mexican States , commonly known as Mexico , is a federal constitutional republic in North America. It is bordered on the north by the United States; on the south and west by the Pacific Ocean; on the southeast by Guatemala, Belize, and the Caribbean Sea; and on the east by the Gulf of...

 subpopulation of Wolf (Canis lupus) which is extinct in the wild. No plant or fungi subpopulations have been assessed by the IUCN.

Local extinction events

Major environmental events, such as volcanic eruptions, may lead to large numbers of local extinctions, such as with the 1980 Mount St. Helens eruption, which led to a fern spike
Fern spike
In paleontology, a fern spike is the occurrence of abundant fern spores in the fossil record, usually immediately after an extinction event...

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