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Minimum viable population (MVP) is a
lower bound Lower may refer to: * Lower (surname) * Lower Township, New Jersey *Lower Receiver (firearms) * Lower Wick Gloucestershire, England See also * Nizhny {{Disambiguation ...
on the population of a species, such that it can survive in the wild. This term is commonly used in the fields of
biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechanisms, Development ...
,
ecology Ecology (from el, οἶκος, "house" and el, -λογία, label=none, "study of") is the study of the relationships between living organisms, including humans, and their physical environment. Ecology considers organisms In biol ...
, and
conservation biology Conservation biology is the study of the conservation of nature and of Earth Earth is the third planet from the Sun and the only astronomical object known to harbour and support life. 29.2% of Earth's surface is land consisting of contine ...
. MVP refers to the smallest possible size at which a biological population can exist without facing extinction from natural disasters or demographic, environmental, or genetic
stochastic Stochastic () refers to the property of being well described by a random In common parlance, randomness is the apparent or actual lack of pattern or predictability in events. A random sequence of events, symbols or steps often has no :wi ...
ity. The term "
population Population typically refers the number of people in a single area whether it be a city or town, region, country, or the world. Governments typically quantify the size of the resident population within their jurisdiction by a process called a ...

population
" is defined as a group of interbreeding individuals in similar geographic area that undergo negligible
gene flow In population genetics Population genetics is a subfield of that deals with genetic differences within and between s, and is a part of . Studies in this branch of examine such phenomena as , , and . Population genetics was a vital ingredient ...

gene flow
with other groups of the species. Typically, MVP is used to refer to a wild population, but can also be used for
ex-situ conservation Svalbard GLOBAL SEED BANK, an ''ex situ'' conservation. ''Ex situ'' conservation literally means, "off-site conservation Conservation is the preservation or efficient use of resources, or the conservation of various quantities under physical laws ...
(Zoo populations).


Estimation

There is no unique definition of what is a sufficient population for the continuation of a species, because whether a species survives will depend to some extent on random events. Thus any calculation of a minimum viable population (MVP) will depend on the population projection model used. A set of random (stochastic) projections might be used to estimate the initial population size needed (based on the assumptions in the model) for there to be (say) a 95% or 99% probability of survival say 1,000 years into the future. Some models use generations as a unit of time rather than years, in order to maintain consistency between
taxa In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechani ...
. These projections ( population viability analyses, or PVA) use
computer simulation Computer simulation is the process of mathematical modelling, performed on a computer, which is designed to predict the behaviour of, or the outcome of, a real-world or physical system. The reliability of some mathematical models can be determ ...
s to model populations using demographic and environmental information to project future
population dynamics Population dynamics is the type of mathematics used to model and study the size and age composition of population Population typically refers the number of people in a single area whether it be a city or town, region, country, or the world. ...
. The probability assigned to a PVA is arrived at after repeating the environmental simulation thousands of times.


Extinction

Small populations are at a greater risk of extinction than larger populations due to small populations having less capacity to recover from adverse stochastic (i.e. random) events. Such events may be divided into four sources: ; Demographic stochasticity : Demographic stochasticity is often only a driving force toward extinction in populations with fewer than 50 individuals. Random events influence the
fecundity Fecundity is defined in two ways; in human demography, it is the potential for reproduction of a recorded population Population typically refers the number of people in a single area whether it be a city or town, region, country, or the wor ...
and survival of individuals in a population, and in larger populations these events tend to be stabilized toward a steady growth rate. However, in small populations there is much more relative variance, which can in turn cause extinction. ; Environmental stochasticity : Small, random changes in the abiotic and
biotic component Biotic components, or biotic factors, can be described as any living component that affects another organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any individual contiguous system th ...
s of the ecosystem that a population inhabits fall under environmental stochasticity. Examples are changes in climate over time, and arrival of another species that competes for resources. Unlike demographic and genetic stochasticity, environmental stochasticity tends to affect populations of all sizes. ; Natural catastrophes : An extension of environmental stochasticity, natural disasters are random, large scale events such as blizzards, droughts, storms, or fires that reduce a population directly within a short period of time. Natural catastrophes are the hardest events to predict, and MVP models often have difficulty factoring these in. ; Genetic stochasticity : Small populations are vulnerable to genetic stochasticity, the random change in
allele An allele (, ; ; modern formation from Greek ἄλλος ''állos'', "other") is one of two, or more, forms of a given gene In biology, a gene (from ''genos'' "...Wilhelm Johannsen coined the word gene to describe the Mendelian_inheritance ...
frequencies over time, also known as
genetic drift Genetic drift (allelic drift or the Sewall Wright effect) is the change in the frequency of an existing gene In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical stru ...

genetic drift
. Genetic drift can cause alleles to disappear from a population, and this lowers genetic diversity. In small populations, low genetic diversity can increase rates of inbreeding, which can result in
inbreeding depression Inbreeding depression is the reduced biological fitness Fitness (often denoted w or ω in population genetics models) is the quantitative representation of natural and sexual selection File:Sexual Selection with Peafowl.gif, 250px, Sexual se ...
, in which a population made up of genetically similar individuals loses fitness. Inbreeding in a population reduces fitness by causing deleterious recessive alleles to become more common in the population, and also by reducing adaptive potential. The so-called "50/500 rule", where a population needs 50 individuals to prevent inbreeding depression, and 500 individuals to guard against genetic drift at-large, is an oft-used benchmark for an MVP, but recent study suggests that this guideline is not applicable across a wide diversity of taxa.


Application

MVP does not take external 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 are generally required for 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. There is a marked trend for , 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 Population density (in agriculture Agriculture is the science, art and practice of cultivating plants and livestock. Agriculture was the key development in the rise of sedentary Image:Family watching television 1958.jpg, Exercise tr ...
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. 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 concerning vertebrates "a cross-species frequency distribution of MVP with a median of 4169 individuals (95% CI = 3577–5129)."


See also

*
Effective population size The effective population size (''N'e'') is the number of individuals that an idealised population would need to have in order for some specified quantity of interest to be the same in the idealised population as in the real population. Idealised ...
*
Human population Humans (''Homo sapiens'') are the most abundant and widespread species In biology, a species is the basic unit of biological classification, classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A speci ...

Human population


References

{{modelling ecosystems, expanded=other Ecological metrics Biostatistics Environmental terminology Habitat