Editing Effective population size (section)

{{short description|Ecological concept}}
{{Technical|date=November 2020}}
The '''effective population size''' (''N''<sub>''e''</sub>) is the size of an [[idealised population]] that would experience the same rate of [[genetic drift]] as the real population.<ref>{{cite web|url=http://www.blackwellpublishing.com/ridley/a-z/Effective_population_size.asp|title=Effective population size|access-date=4 March 2018|work=[[Blackwell Publishing]]}}</ref> Idealised populations are those following simple one-[[Locus (genetics)|locus]] models that comply with assumptions of the [[neutral theory of molecular evolution]]. The effective population size is normally smaller than the [[population size|census population size]] ''N'', partly because chance events prevent some individuals from breeding, and partly due to [[background selection]] and [[genetic hitchhiking]].

The same real population could have a different effective population size for different properties of interest, such as genetic drift (or more precisely, the speed of [[Coalescent theory#Time to coalescence|coalescence]]) over one generation vs. over many generations. Within a species, [[Locus (genetics)|areas]] of the genome that have more [[gene]]s and/or less [[genetic recombination]] tend to have lower effective population sizes, because of the effects of selection at linked sites. In a population with selection at many loci and abundant [[linkage disequilibrium]], the coalescent effective population size may not reflect the census population size at all, or may reflect its logarithm.

The concept of effective population size was introduced in the field of [[population genetics]] in 1931 by the [[United States|American]] [[geneticist]] [[Sewall Wright]].<ref>{{cite journal |author=Wright S |year=1931 |title=Evolution in Mendelian populations |journal=[[Genetics (journal)|Genetics]] |volume=16 |issue=2 |pages=97–159 |doi=10.1093/genetics/16.2.97 |pmid=17246615 |pmc=1201091 |url=http://www.esp.org/foundations/genetics/classical/holdings/w/sw-31.pdf}}</ref><ref>{{cite journal |author=Wright S |year=1938 |title=Size of population and breeding structure in relation to evolution |journal=[[Science (journal)|Science]] |volume=87 |pages=430–431 | doi = 10.1126/science.87.2263.425-a |issue=2263}}</ref> Some versions of the effective population size are used in wildlife conservation.