Based on these assumptions, Fig. 4.15 shows the expected levels of genetic differentiation among infinitely many island model subpopulations for different levels of the product of the effective population size of each deme and the migration rate among demes (Nem). When Nem - sometimes called the effective migration rate - is large, very little differentiation among demes is expected for a diploid locus since the combination of the effective size of demes and the migration rate is large enough to overcome the genetic differentiation caused by genetic drift. As the effective migration rate declines from a relatively large value such as Nem = 10, genetic differentiation among demes increases slowly at first and then rapidly once the effective migration rate is less than about 1. An effective migration rate of one individual every other generation

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