Estimating the Effective Population Size of Conserved Populations

Nunney, Leonard; Elam, Diane R.

doi:10.1046/j.1523-1739.1994.08010175.x

Cited by 279 publications

(356 citation statements)

References 16 publications

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“…Table 1 summarizes the notation used. Following Nunney and Elam (1994), N is defined as the adult population size (all mature individuals, including those that might not breed in a given year). In the model, x is used as an index of age, and hence N x represents the number of individuals alive at any given time that are age x. Age-specific vital rates that we will be concerned with include m x = mean number of offspring per year produced by an individual of age x; s x = probability of survival from age x to age x+1; d x = 1 − s x = probability of dying between age x and age x+1; and l x = cumulative survival through age x (with l 1 = 1 and l x ¼ Q x41 s xÀ1 ).…”

Section: Notation and The Agene Modelmentioning

confidence: 99%

“…Much of what we know about how life-history traits influence N e and the ratio of effective size to census size (N) when generations overlap is because of a body of work by Len Nunney during the 1990s (Nunney, 1991(Nunney, , 1993Nunney and Elam, 1994;Nunney, 1996). These studies evaluated the influence of a variety of factors, including primary and secondary sex ratio, mating system, variation in fecundity, generation length and the way N is defined in computing the N e /N ratio.…”

Section: Introductionmentioning

confidence: 99%

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Life-history traits and effective population size in species with overlapping generations revisited: the importance of adult mortality

Waples

2016

Heredity

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The relationship between life-history traits and the key eco-evolutionary parameters effective population size (N e ) and N e /N is revisited for iteroparous species with overlapping generations, with a focus on the annual rate of adult mortality (d). Analytical methods based on populations with arbitrarily long adult lifespans are used to evaluate the influence of d on N e , N e /N and the factors that determine these parameters: adult abundance (N), generation length (T), age at maturity (α), the ratio of variance to mean reproductive success in one season by individuals of the same age (ϕ) and lifetime variance in reproductive success of individuals in a cohort (V k• ). Although the resulting estimators of N, T and V k• are upwardly biased for species with short adult lifespans, the estimate of N e /N is largely unbiased because biases in T are compensated for by biases in V k• and N. For the first time, the contrasting effects of T and V k• on N e and N e /N are jointly considered with respect to d and ϕ. A simple function of d and α based on the assumption of constant vital rates is shown to be a robust predictor (R 2 = 0.78) of N e /N in an empirical data set of life tables for 63 animal and plant species with diverse life histories. Results presented here should provide important context for interpreting the surge of genetically based estimates of N e that has been fueled by the genomics revolution.

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Section: Notation and The Agene Modelmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Life-history traits and effective population size in species with overlapping generations revisited: the importance of adult mortality

Waples

2016

Heredity

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“…The effective population size is difficult to estimate in natural populations (Pope 1996), and the ratio of effective population size to census population size (N e /N) can vary widely depending on the life history of the organism in question (Nunney 1995). Previous studies found that for long-lived species with overlapping generations, the effective population size is generally close to half of the breeding adult number (Nunney 1991(Nunney , 1993Nunney and Elam 1994). We found that adults account for approximately 92% of the IL population, and Legler (1960) reported a Kansas population consisting of 84% adults.…”

Section: Genetic Diversity Projections For the Il Populationmentioning

confidence: 99%

Genetic Effects of a Persistent Bottleneck on a Natural Population of Ornate Box Turtles (Terrapene ornata)

Kuo

Janzen

2004

Conservation Genetics

139

105

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Human activities in the past few hundred years have caused enormous impacts on many ecosystems, greatly accelerating the rate of population decline and extinction. In addition to habitat alteration and destruction, the loss of genetic diversity due to reduced population size has become a major conservation issue for many imperiled species. However, the genetic effects of persistent population bottlenecks can be very different for long-lived and short-lived species when considering the time scale of centuries. To investigate the genetic effects of persistent population bottlenecks on long-lived species, we use microsatellite markers to assess the level of genetic diversity of a small ornate box turtle population that has experienced a persistent bottleneck in the past century, and compare it to a large relatively undisturbed population. The genetic signature of a recent bottleneck is detected by examining the deviation from mutation-drift equilibrium in the small population, but the bottleneck had little effect on its level of genetic diversity. Computer simulations combined with information on population structure suggest that an effective population size of 300, which results in a census population size of 700, would be required for the small population to maintain 90% of the average number of alleles per locus in the next 200 years. The life history of long-lived species could mask the accelerated rate of genetic drift, making population recovery a relatively slow process. Statistical analysis of genetic data and empirical-based computer simulations can be important tools to facilitate conservation planning.

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“…One parameter, which is often important to monitor, is the effective population size (N e ; Nunney and Elam, 1994;Frankham, 2005;Charlesworth, 2009) because it reflects the rate of inbreeding and amount of genetic variation expected to be lost due to genetic drift each generation. Multiple studies have successfully estimated N e over time periods separated by several generations.…”

Section: Introductionmentioning

confidence: 99%

Genetic monitoring reveals temporal stability over 30 years in a small, lake-resident brown trout population

2012

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Knowledge of the degree of temporal stability of population genetic structure and composition is important for understanding microevolutionary processes and addressing issues of human impact of natural populations. We know little about how representative single samples in time are to reflect population genetic constitution, and we explore the temporal genetic variability patterns over a 30-year period of annual sampling of a lake-resident brown trout (Salmo trutta) population, covering 37 consecutive cohorts and five generations. Levels of variation remain largely stable over this period, with no indication of substructuring within the lake. We detect genetic drift, however, and the genetically effective population size (N e ) was assessed from allele-frequency shifts between consecutive cohorts using an unbiased estimator that accounts for the effect of overlapping generation. The overall mean N e is estimated as 74. We find indications that N e varies over time, but there is no obvious temporal trend. We also estimated N e using a one-sample approach based on linkage disequilibrium (LD) that does not account for the effect of overlapping generations. Combining one-sample estimates for all years gives an N e estimate of 76. This similarity between estimates may be coincidental or reflecting a general robustness of the LD approach to violations of the discrete generations assumption. In contrast to the observed genetic stability, body size and catch per effort have increased over the study period. Estimates of annual effective number of breeders (N b ) correlated with catch per effort, suggesting that genetic monitoring can be used for detecting fluctuations in abundance.

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Estimating the Effective Population Size of Conserved Populations

Cited by 279 publications

References 16 publications

Life-history traits and effective population size in species with overlapping generations revisited: the importance of adult mortality

Life-history traits and effective population size in species with overlapping generations revisited: the importance of adult mortality

Genetic Effects of a Persistent Bottleneck on a Natural Population of Ornate Box Turtles (Terrapene ornata)

Genetic monitoring reveals temporal stability over 30 years in a small, lake-resident brown trout population

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