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A basic assumption of population genetics is that all individuals have an equal probability of reproducing and the actual number of (surviving to reproduction) offpsring are Poisson distributed with an average of two in a population of constant size. However, there is evidence that many natural populations have very unequal probabilities of reproduction. This reduces the effective population size below the census size because alleles are inherited through a smaller number of individuals. Culver et al. (2008) cite Lande & Barrowclough (1987) and give the following relationships for females (f) and males (m), which are likely to have different reproductive probabilities.

k is the average number of offpsring per individual and Vk is the variance in the number of offpsring.

In an ideal population of constant size k=2 and Vk=2. Ne,f = (2Nf-1)/(2-1+2/2) = (2Nf-1)/(2) = Nf - 1/2


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Floyd A. Reed, December 27, 2020 – Jannuary 5, 2021