The process by which groups of living organisms expand the space or range within which they live. Dispersal operates when individual organisms leave the space that they have occupied previously, or in which they were born, and settle in new areas. Natal dispersal is the first movement of an organism from its birth site to the site in which it first attempts to breed. Adult dispersal is a subsequent movement when an adult organism changes its location in space. As individuals move across space and settle into new locations, the population to which they belong expands or contracts its overall distribution. Thus, dispersal is the process by which populations change the area they occupy.