You overestimate the rate of emergence of relevant mutations. In the explosive range-expansion phase most lineages have zero functional difference from each other and almost all expansion of particular lineages comes from chance invasions of large vulnerable populations.
There is a reason that when a species suddenly has a range-expansion event, you actually see a relaxation of selection and a buildup of deleterious mutations...
You overestimate the rate of emergence of relevant mutations. In the explosive range-expansion phase most lineages have zero functional difference from each other and almost all expansion of particular lineages comes from chance invasions of large vulnerable populations.
There is a reason that when a species suddenly has a range-expansion event, you actually see a relaxation of selection and a buildup of deleterious mutations...