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In ecology, extinction debt is the future extinction of species due to events in the past. Extinction debt occurs because of time delays between impacts on a species, such as destruction of habitat, and the species' ultimate disappearance. For instance, long-lived trees may survive for many years even after reproduction of new trees has become impossible, and thus they may be committed to extinction. Technically, extinction debt generally refers to the ''number of species'' in an area likely to go extinct, rather than the prospects of any one species, but colloquially it refers to any occurrence of delayed extinction. In discussions of threats to biodiversity, extinction debt is analogous to the "climate commitment" in climate change, which states that inertia will cause the earth to continue to warm for centuries even if no more greenhouse gasses are emitted. Similarly, the current extinction may continue long after human impacts on species halt. Extinction debt may be local or global, but most examples are local as these are easier to observe and model. It is most likely to be found in long-lived species and species with very specific habitat requirements (specialists).〔 Extinction debt has important implications for conservation, as it implies that species may go extinct due to past habitat destruction, even if continued impacts cease, and that current reserves may not be sufficient to maintain the species that occupy them. Interventions such as habitat restoration may reverse extinction debt. ''Immigration credit'' is the corollary to extinction debt. It refers to the number of species likely to immigrate to an area after an event such as the restoration of an ecosystem. == Causes == Extinction debt is caused by many of the same drivers as extinction. The most well-known drivers of extinction debt are habitat fragmentation and habitat destruction. These cause extinction debt by reducing the ability of species to persist via immigration to new habitats. Under equilibrium conditions, species may go extinct in one habitat patch, yet continues to survive because it can disperse to other patches. However, as other patches have been destroyed or rendered inaccessible due to fragmentation, this "insurance" effect is reduced and the species may ultimately go extinct. Pollution may also cause extinction debt by reducing a species' birth rate or increasing its death rate so that its population slowly declines.〔 Extinction debts may be caused by invasive species or by climate change. Extinction debt may also occur due to the loss of mutualist species. In New Zealand, the local extinction of several species of pollinating birds in 1870 has caused a long-term reduction in the reproduction of the shrub species ''Rhabdothamnus solandri'', which requires these birds to produce seeds. However, as the plant is slow-growing and long-lived, its populations persist. 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「Extinction debt」の詳細全文を読む スポンサード リンク
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