What does it mean by effective population size?
The effective population size can only be defined if you understand random genetic drift. The effective population size loses heterozygosity (to drift) at a rate equal to an idealized population of the same size. An idealized population all individuals breed, the sex ratio is 1:1, population size does not change through time, and the distribution of offspring per female is a Poisson. There are other assumptions, but these are the biggest. Effective population size is smaller than actual population size in all natural populations because none of these assumptions hold. Most importantly population size does change through time, not all individuals breed, and the number of offspring born to females is often overdispersed compared to a Poisson (the variance is larger than the mean). This causes genetic diversity to be lost faster than ‘expected’ and effective population size is smaller than actual. One way to think about it is with the example of the sex ratios. If you have one male that y
