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Coextinction and cothreatened refer to the phenomena of the loss or decline of a host species resulting in the loss or endangerment of other species that depend on it, potentially leading to cascading effects across trophic levels. The term originated by the authors Stork and Lyal (1993) and was originally used to explain the extinction of parasitic insects following the loss of their specific hosts. The term is now used to describe the loss of any interacting species, including predators with their prey, and specialist herbivores with their food source. Coextinction is especially common when a keystone species goes extinct. ==Causes== The most often cited example is that of the extinct passenger pigeon and its parasitic bird lice ''Columbicola extinctus'' and ''Campanulotes defectus''. Recently, ''C. extinctus'' was rediscovered on the band-tailed pigeon, and ''C. defectus'' was found to be a likely case of misidentification of the existing ''Campanulotes flavus''. However, even though the passenger pigeon lice story has a happy ending (i.e. rediscovery), coextinctions of other parasites, even on the passenger pigeon, may have occurred. Several louse species—such as ''Rallicola extinctus'', a huia parasite - probably became extinct together with their hosts. In recent studies, up to 50% of species have been said to go extinct in the next 50 years. This may be possible due to an example of coextinction being the loss of tropical butterfly species from Singapore attributing to the loss of their specific larval host plants.〔 To see how possible future cases of coextinction would play out, researchers have made models to show probabilistic relationships between affiliate and host extinctions across co-evolved inter-specific systems. The subjects are pollinating Ficus Wasps and Ficus, primate parasites, (Pneumocystis Fungi, Nematode, and Lice) and their hosts, parasitic mites and lice and their avian hosts, butterflies and their larval host plants, and ant butterflies and their host ants. For all but the most host-specific affiliate groups (e.g., primate Pneumocystis fungi and primates), affiliate extinction levels may be modest at low levels of host extinction but can be expected to rise quickly as host extinctions increase to levels predicted in the near future. This curvilinear relationship between host and affiliate extinction levels may also explain, in part, why so few coextinction events have been documented to date(Koh ''et al''2004). Recent investigations of coextinction risk among the rich Psyllid fauna Hemiptera: Psylloidea inhabiting acacias (Fabaceae-Mimosoideae: Acacia) in central eastern New South Wales, Australia provide information about coextinction. The results, derived from simple criteria to name host specialists among threatened acacias in Australia’s central east, suggest that A. ausfeldii hosts one specialist psyllid species, Acizzia, and that A. gordonii hosts one specialist psyllid, Acizzia. Both psyllid species may be threatened at the same level of their host species with coextinction. Interaction patterns can be used to anticipate the consequences of phylogenetic effects. By using a system of methodical observations, scientists can use the phylogenetic relationships of species to predict the number of interactions they exhibit in more than one-third of the networks, and the identity of the species with which they interact in about half of the networks. Consequentially, simulated extinction events tend to trigger coextinction cascades of related species. This results in a non-random pruning of the evolutionary tree. In a 2004 paper in ''Science'', ecologist Lian Pin Koh and colleagues discuss coextinction, stating "Species coextinction is a manifestation of the interconnectedness of organisms in complex ecosystems. The loss of species through coextinction represents the loss of irreplaceable evolutionary and coevolutionary history. In view of the global extinction crisis, it is imperative that coextinction be the focus of future research to understand the intricate processes of species extinctions. While coextinction may not be the most important cause of species extinctions, it is certainly an insidious one." (Koh ''et al.'' 2004) Koh ''et al.'' also define coendangered as taxon "likely to go extinct if their currently endangered hosts () become extinct." One example is the near extinction of the genus ''Hibiscadelphus'' as a consequence of the disappearance of several of the Hawaiian honeycreepers, its pollinators. There are several instances of predators and scavengers dying out following the disappearance of species which represented their source of food: for example, the coextinction of the Haast's eagle with the moa. Coextinction may also occur on a local level: for example, the decline in the red ant ''Myrmica sabuleti'' in southern England, caused by habitat loss, resulted in the local extinction of the large blue butterfly, which is dependent on the ant as a host for the larvae. In this case the ant avoided local extinction, and the butterfly has been reintroduced. Another example of species going through coextinction is rhinoceros stomach bot fly (Gyrostigma rhinocerontis) and of its host species the endangered black rhinoceros (Diceros bicornis) and the white rhinoceros (Ceratotherium simum). The female fly lays eggs behind the rhinoceros' ears or horns or neck and then the flies' larvae enter the animal's digestive tract and digs into the stomach lining and then are excreted out and the lifecycle restarts. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Coextinction」の詳細全文を読む スポンサード リンク
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