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Population bottleneck
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{{Short description|Effects of a sharp reduction in numbers on the diversity and robustness of a population}} [[File:Population bottleneck.svg|thumb|right|Population bottleneck followed by recovery or extinction]] A '''population bottleneck''' or '''genetic bottleneck''' is a sharp reduction in the size of a [[population]] due to environmental events such as [[famines]], [[earthquakes]], [[floods]], fires, [[disease]], and [[drought]]s; or human activities such as [[genocide]], [[Extinction|speciocide]], widespread violence or intentional [[culling]]. Such events can reduce the variation in the [[gene pool]] of a population; thereafter, a smaller population, with a smaller [[genetic diversity]], remains to pass on genes to [[future generations]] of [[offspring]]. Genetic diversity remains lower, increasing only when gene flow from another population occurs or very slowly increasing with time as random [[mutation]]s occur.<ref>William R. Catton, Jr. "Bottleneck: Humanity's Impending Impasse" Xlibris Corporation, 2009. 290 pp. {{ISBN|978-1-4415-2241-2}}{{page needed|date=March 2014}}{{self-published source|date=December 2017}}</ref>{{Self-published inline|certain=yes|date=December 2017}} This results in a reduction in the robustness of the population and in its ability to adapt to and survive [[natural selection|selecting]] environmental changes, such as [[Climate change (general concept)|climate change]] or a shift in available resources.<ref>{{cite journal |last=Lande |first=R. |year=1988 |title=Genetics and demography in biological conservation |journal=Science |volume=241 |issue=4872 |pages=1455β1460 |doi=10.1126/science.3420403 |pmid=3420403 |bibcode=1988Sci...241.1455L }}</ref> Alternatively, if survivors of the bottleneck are the individuals with the greatest genetic [[Fitness (biology)|fitness]], the frequency of the fitter genes within the gene pool is increased, while the pool itself is reduced. [[File:Bottleneck Effect.jpg|thumb|How a natural disaster leads to a reduction in genetic diversity in the population due to a drastic reduction in size.]] The [[genetic drift]] caused by a population bottleneck can change the proportional random distribution of [[allele]]s and even lead to [[Fixation (population genetics)|loss of alleles]]. The chances of [[inbreeding]] and genetic homogeneity can increase, possibly leading to [[inbreeding depression]]. Smaller population size can also cause deleterious mutations to accumulate.<ref>{{cite journal |last1=Lynch |first1=M. |last2=Conery |first2=J. |last3=Burger |first3=R. |year=1995 |title=Mutation accumulation and the extinction of small populations |journal=The American Naturalist |volume=146 |issue=4 |pages=489β518 |doi=10.1086/285812 |bibcode=1995ANat..146..489L |s2cid=14762497 }}</ref> Population bottlenecks play an important role in [[conservation biology]] (see [[minimum viable population]] size) and in the context of agriculture (biological and [[pest control]]).<ref>{{cite journal |vauthors=Hufbauer RA, Bogdanowicz SM, Harrison RG |title=The population genetics of a biological control introduction: mitochondrial DNA and microsatellie variation in native and introduced populations of Aphidus ervi, a parasitoid wasp |journal=Molecular Ecology |volume=13 |issue=2 |pages=337β48 |date=February 2004 |pmid=14717891 |doi=10.1046/j.1365-294X.2003.02084.x|bibcode=2004MolEc..13..337H |s2cid=45796650 }}</ref>
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