Wild populations are smaller than we think: a commentary on 'Effective population size/adult population size ratios in wildlife: a review' by Richard Frankham.
{"title":"Wild populations are smaller than we think: a commentary on 'Effective population size/adult population size ratios in wildlife: a review' by Richard Frankham.","authors":"T. Mackay","doi":"10.1017/S0016672308009701","DOIUrl":null,"url":null,"abstract":"where H0 is the heterozygosity of the population before the bottleneck, Ht is the heterozygosity after t generations of maintenance with 2N individuals and F is the inbreeding coefficient (Falconer & Mackay, 1996). Clearly heterozygosity decreases, and inbreeding increases, as N decreases ; and these effects accumulate over time. However, no real population fits the ideal model on which this theory is based, which includes self-fertilization in random amounts. The concept of effective population size enables us to utilize this expression by replacing the N in the equation with Ne, where Ne, the effective population size, is the number of individuals that would give rise to the same variance in gene frequency or rate of inbreeding as an ideal population of that size (Falconer & Mackay, 1996). Major departures from the ideal population model that affect Ne are unequal numbers of males and females, unequal numbers of individuals in different generations, non-random distribution of family size, and overlapping generations. Analytical expressions relating the census size of the population (N) to the effective population size have been derived for each of these cases (Frankham, 1995; Falconer & Mackay, 1996) ; under most scenarios Ne<N. Knowledge of the ratio ofNe toN is critical in wildlife populations and particularly endangered species, if we are to predict the rate of inbreeding and loss of heterozygosity. In this meta-analysis, Frankham (1995) synthesizes data from 192 estimates of Ne/N from 102 species. The estimates of Ne/N from insects, molluscs, amphibians, reptiles, birds, mammals and plants ranged from 10x6 in Pacific oysters to 0.99 in humans, and averaged 0.34 overall. However, these studies differed in whether they included fluctuating population size, variable family size and/or different numbers of males and females – less than one-third of the studies included all three of these factors. In addition, different measures of census size were used as the denominator. Some studies utilized the total census size (NT, the total number of adults and juveniles), some the number of adults (NA, the number of breeding plus senescent adults), while others counted only the number of breeding individuals (NB). Finally, both genetic and demographic methods were used. Frankham (1995) capitalized on this variability to perform stepwise regression analyses in order to determine the major variables affecting Ne/N. The significant variables, in decreasing order of importance, were fluctuating population size, variable family size, method of determining census number, taxonomic group, and the sex ratio. The most striking conclusion was that the comprehensive estimates of Ne/N in wild species, including all variables, were of the order of 10%. This is much smaller than had been thought previously and a cause for concern in terms of long-term population viability. This influential review stimulated many studies estimating Ne/N in a wide variety of wild species.","PeriodicalId":12777,"journal":{"name":"Genetical research","volume":"38 1","pages":"489"},"PeriodicalIF":0.0000,"publicationDate":"2007-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"3","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Genetical research","FirstCategoryId":"1085","ListUrlMain":"https://doi.org/10.1017/S0016672308009701","RegionNum":0,"RegionCategory":null,"ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"","JCRName":"","Score":null,"Total":0}
引用次数: 3
Abstract
where H0 is the heterozygosity of the population before the bottleneck, Ht is the heterozygosity after t generations of maintenance with 2N individuals and F is the inbreeding coefficient (Falconer & Mackay, 1996). Clearly heterozygosity decreases, and inbreeding increases, as N decreases ; and these effects accumulate over time. However, no real population fits the ideal model on which this theory is based, which includes self-fertilization in random amounts. The concept of effective population size enables us to utilize this expression by replacing the N in the equation with Ne, where Ne, the effective population size, is the number of individuals that would give rise to the same variance in gene frequency or rate of inbreeding as an ideal population of that size (Falconer & Mackay, 1996). Major departures from the ideal population model that affect Ne are unequal numbers of males and females, unequal numbers of individuals in different generations, non-random distribution of family size, and overlapping generations. Analytical expressions relating the census size of the population (N) to the effective population size have been derived for each of these cases (Frankham, 1995; Falconer & Mackay, 1996) ; under most scenarios Ne
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