 Wright introduced two different models of population structure, one not taking short-distance dispersal into account and one model incorporating short-distance dispersal.The "island model" is quite artificial and proposes the idea that a population is divided into two geographically, unique subpopulations (islands) with random mating occurring with exchange of individuals occurring when a migrant is drawn randomly from the total population.In a more realistic model, where short-distance dispersal is taken into account, a population is compiled of continuously distributed individuals over a region of space.