It varies with the gene form 0 for waxy in corn to very slow. What ever the cause, mutations usually occur at a more or less constant rate. A formula to determine the number of generations required for mutation alone to create a new equilibrium can be obtained by simple calculus as. So we can see that it would take a very long time for mutation alone to have a significant effect in changing an equilibrium. A populations can acquire new alleles via either mutation or via immigration.
Immigration is tied to the dispersal ability of the species.
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.