Minimum viable population is usually estimated as the population size necessary to ensure between 90 and 95 percent probability of survival between 100 to 1,000 years into the future. The MVP can be estimated using
computer simulations for
population viability analyses (PVA). PVA models populations using demographic and environmental information to project future population dynamics. The probability assigned to a PVA is arrived at after repeating the environmental simulation thousands of times.
For example, for a theoretical simulation of a population of 50 giant pandas in which the simulated population goes completely extinct, 30 out of 100 stochastic simulations projected 100 years into the future are not viable. Causes of extinction in the simulation may include
inbreeding depression,
natural disaster, or
climate change. Extinction occurring in 30 out of 100 runs would give a survival probability of 70%. In contrast, in the same simulation with a starting population of 60 pandas, the panda population may only become extinct in four of the hundred runs, resulting in a survival probability of 96%. In this case the minimum viable population that satisfies the 90- to 95% probability for survival is between 50 and 60 pandas. (These figures have been invented for the purpose of this example.)
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]
There is 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. An MVP of 500 to 1,000 has often been given as an average for terrestrial vertebrates when inbreeding or genetic variability is ignored.
[3][4] When inbreeding effects are included, estimates of MVP for many species are in the thousands. Based on a meta-analysis of reported values in the literature for many species, Traill
et al. reported a median MVP of 4,169 individuals.
[5]
