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docs/2_Theoretical_background/Ne-500.md

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 The Ne 500 indicator is derived by comparing **the effective population size (Ne) of each population to a critical threshold**, 500, and reporting the proportion of populations above the threshold and therefore maintaining genetic diversity. 
 
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 ![](Ne500_Fig1.png)
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 ###### Fig 2.2 *The relationship between effective population size and genetic diversity. Small populations lose genetic diversity more rapidly than large populations, often leading to inbreeding depression and ultimately the complete collapse of the population (extinction). Populations above Ne 500 are capable of maintaining genetic diversity into the long-term.*
 
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 The Ne of a population can be estimated with statistical methods and DNA sequence data, when that is available. But for nearly all species, such DNA analysis is not yet available. For many species, it is sufficient and appropriate to obtain the Ne by using a simple transformation of **census size Nc (the number of mature individuals) e.g. using an Ne:Nc ratio.**
 
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 ![](Ne500_Fig2.png)
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 ###### Fig 2.3
 
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 An Ne:Nc conversion ratio of 0.1 generally a conservative and suitable ratio to calculate gauge Ne (although typical ratios may range from 0.1 to about 0.3 in many vertebrates and plants - this is a generalization). **By applying a 0.1 Ne:Nc ratio, Ne 500 translates to a threshold of Nc = 5000** mature individuals.  
 
 Once each population has an Ne value, they are compared against the threshold value of 500. The number of populations with Ne > 500 are summed and divided by the total number of existing populations. For example, a species has 5 populations remaining, 3 of which are above Ne 500. The indicator value for this species would be 3/5 = 0.6.