Dispersal, Dispersal Patterns Dispersal Ranges for most species show that most individuals of a population stay close to home with few dispersing long distance. This means that effective population sizes are smaller than they seem. Fruit flies in Hawaii are essentially prevented from migrating to adjacent by a Lava flow of only a few meters in width. A migration rate of '0' means no gene movement into the population whereas a value of '1' means total swamping of resident population. Immigration rates are going to vary with distance to nearest population.
Dispersal only is of value if gene frequency of incoming individuals are different than residents.
Multiplying the average distance dispersed times the number generation gives a rough estimate of how far and how fast a gene can move through time. If we know 4 of the 5, then we can calculate the fifth. Such a case was worked out for Rh blood proteins in a population of black Africans brought to the US during the slave trade. It was the goal to measure the amount of gene migration from the white American population into the black population. A population of isolated black African village was used to represent the original African frequencies.