Another option is to look for genetic markers in the invaders. When a population expsndd from a small base, whatever allelee common in that base become common i

Another option is to look for genetic markers in the invaders. When a population expsndd from a small base, whatever allelee common in that base become common in the expanded population even when these alleles are uncommon in the species as a whole. https://en.m.wikipedia.org/wiki/Founder_effect https://en.m.wikipedia.org/wiki/Founder_effect