constant population definition

Copyright © 2005 by Houghton Mifflin Harcourt Publishing Company.

Suppose it is of interest to estimate the population mean, μ, for a quantitative variable.

She has published numerous peer-reviewed journal articles on nanotechnology and materials science. In statistics, a population refers to all the members of a group of people or things.

there is no self-fertilisation then. Population, in human biology, the whole number of inhabitants occupying an area (such as a country or the world) and continually being modified by increases (births and immigrations) and losses (deaths and emigrations).

For example, when people are asked whether they approve or disapprove of a particular political leader, typically there is uncertainty about what the response will be. The presentation follows Kempthorne (1957).


Get exclusive access to content from our 1768 First Edition with your subscription. The absolute value of the difference between the sample mean, x̄, and the population mean, μ, written |x̄ − μ|, is called the sampling error.

According to the neutral theory of molecular evolution, a neutral allele remains in a population for Ne generations, where Ne is the effective population size. Our editors will review what you’ve submitted and determine whether to revise the article.

Human populations are further affected by social customs governing reproduction and by the technological developments, especially in medicine and public health, that have reduced mortality and extended the life span. For instance, interval estimation of a population variance, standard deviation, and total can be required in other applications. The Malthusian Theory of Population Definition. In an idealised diploid population with no selection at any locus, the expectation of the coalescence time in generations is equal to twice the census population size.


Consider, for example, the population mean, μ. Then the effective population size is the harmonic mean of these, giving: Note this is less than the arithmetic mean of the population size, which in this example is 126.7. When the sample mean is used as a point estimate of the population mean, some error can be expected owing to the fact that a sample, or subset of the population, is used to compute the point estimate. In the large-sample case, a 95% confidence interval estimate for the population mean is given by x̄ ± 1.96σ/Square root of√n. Population genetics is the study of how selective forces change a population through changes in allele and genotypic frequencies. You can also apply this rate to calculate doubling time of human population.

[5] Another important effective population size is the selection effective population size 1/scritical, where scritical is the critical value of the selection coefficient at which selection becomes more important than genetic drift.[6].

Meanwhile, women in much of Europe and North America averaged about two children per woman during the 1970s and 1980s—a number 80 percent less than that achieved by the Hutterites. Accordingly, the ratios ranged widely from 10-6 for Pacific oysters to 0.994 for humans, with an average of 0.34 across the examined species. (

[4], Today, the effective population size is usually estimated empirically with respect to the sojourn or coalescence time, estimated as the within-species genetic diversity divided by the mutation rate, yielding a coalescent effective population size. and solving for In statistics, a population parameter is a number that describes something about an entire group or population. If you encounter a problem downloading a file, please try again from a laptop or desktop. Demography casts a multidisciplinary net, drawing insights from economics, sociology, statistics, medicine, biology, anthropology, and history. There is no dispute as to the fact and magnitudes of such declines, but theoretical explanation of the phenomena has proved elusive. 2: However, in natural populations the variance is often larger than this.

(Confusingly, these English terms have opposite meanings from their parallel terms in French, where fertilité is the potential and fécondité is the realized; similarly ambiguous usages also prevail in the biological sciences, thereby increasing the chance of misunderstanding.) is the mutation rate. Ne, where Population genetics is the study of how selective forces change a population through changes in allele and genotypic frequencies.

The effective population size 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. The quantity σ/Square root of√n is the standard error, and 1.96 is the number of standard errors from the mean necessary to include 95% of the values in a normal distribution.

The sojourn effective population size can therefore be estimated empirically by dividing the nucleotide diversity by the mutation rate.[5].

You should also make sure your sample size, or number of things you are studying, is large enough so that your data becomes statistically significant: it accurately estimates the true statistics regarding a population. In an idealised Wright-Fisher model, the fate of an allele, beginning at an intermediate frequency, is largely determined by selection if the selection coefficient s ≫ 1/N, and largely determined by neutral genetic drift if s ≪ 1/N.

Consider, for example, the population mean, μ.

the maintenance of a population at a constant level by limiting the number of live births to that needed to replace the existing population.

For coalescent effective population sizes, a survey of publications on 102 mostly wildlife animal and plant species yielded 192 Ne/N ratios. ′ [6][18] This limit to selection in a real population may be captured in a toy Wright-Fisher simulation through the appropriate choice of Ne.


A sample is a part, or a subset, of a population. {\displaystyle N_{e}^{(v)}}

where D represents dioeciousness and may take the value 0 (for not dioecious) or 1 for dioecious. var

At its most basic level, the components of population change are few indeed. μ

[19][20], Overview: Types of effective population size, Theoretical example: overlapping generations and age-structured populations, "Wright and Fisher on Inbreeding and Random Drift", "Genetic Draft and Quasi-Neutrality in Large Facultatively Sexual Populations", "Generation time and effective population size in Polar Eskimos", "Inbreeding in populations with overlapping generations", "Limits to the Rate of Adaptive Substitution in Sexual Populations", "Evolution of molecular error rates and the consequences for evolvability",, Latitudinal gradients in species diversity,, Creative Commons Attribution-ShareAlike License, This page was last edited on 31 October 2020, at 21:05.

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