Minimum viable population
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Minimum viable population (MVP) is a lower bound on the population of a species, such that it can survive in the wild. This term is used in the fields of biology, ecology and conservation biology. More specifically MVP is the smallest possible size at which a biological population can exist without facing extinction from natural disasters or demographic, environmental, or genetic stochasticity.[1] The term "population" refers to the population of a species in the wild. For example, the undomesticated dromedary is extinct in its natural wild habitat; but there is a domestic population in captivity and an additional feral population in Australia. Two groups of house cats in separate houses which are not allowed outdoors are also technically distinct populations. Typically, however, MVP is used to refer solely to a wild population, such as the red wolf.
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[edit] Estimating the MVP
As a reference standard, MVP is usually given with a population survival probability of somewhere between ninety and ninety-five percent and calculated for between one hundred and one thousand years into the future.
The MVP can be calculated using computer simulations known as population viability analyses (PVA), where populations are modelled and future population dynamics are projected.
For example, a PVA (essentially a computer simulation of the population) might be run repeatedly on a giant panda population. It might be found that with a starting population of fifty pandas, the simulated population goes completely extinct thirty out of one hundred stochastic runs of the simulation when projected one hundred years into the future. Various causes may include inbreeding depression, natural disaster, or climate change. Extinction occurring thirty out of one hundred runs would give a survival probability of seventy percent. In the same simulation, but with a starting population of sixty pandas, the panda population may only go extinct on four of the hundred runs. It is said in such a situation that the panda population is large enough to recover from or to "buffer" the effects of stochastic events. Thus the minimum viable population is (somewhat arbitrarily) sixty pandas. The simulation would be repeated with a larger range of starting sizes to more closely determine the figure. (Note: These statistics were invented for the purpose of this example.)
[edit] MVP and extinction
MVP does not take human intervention into account. Thus, it is useful for conservation managers and environmentalists; a population may be increased above the MVP using a captive breeding program, or by bringing other members of the species in from other reserves.
There is naturally some debate on the accuracy of PVAs, since a wide variety of assumptions generally are required for future forecasting; however, the important consideration is not absolute accuracy, but promulgation of the concept that each species indeed has an MVP, which at least can be approximated for the sake of conservation biology and Biodiversity Action Plans.[2][verification needed]
There are a marked trend for insularity, surviving genetic bottlenecks and r-strategy to allow far lower MVPs than average. Conversely, taxa easily affected by inbreeding depression – having high MVPs – are often decidedly K-strategists, with low population densities while occurring over a wide range. While an MVP of 50 is often given as average for terrestrial vertebrates, MVPs of far lower than 10 are proven to exist and e.g. tigers seem to have MVPs in the low-mid hundreds, judging from their rapidly accelerating decline in the last decades.
[edit] See also
[edit] Footnotes
[edit] References
- Holsinger, Kent (2007): Types of stochastic threats. Version of 2007-SEP-04. Retrieved 2007-NOV-04.
- Shaffer, M.L. (1981): Minimum Population Sizes for Species Conservation. BioScience 31(2): 131–134. doi:10.2307/1308256 (HTML abstract, first page image)
