>Presumably the same things that cause your "native" population to stop reproducing eventually affects your immigrants after a generation or so, so while it can

>Presumably the same things that cause your "native" population to stop reproducing eventually affects your immigrants after a generation or so, so while it can definitely slow the population decline, it's not a full solution. I think it could be a full solution. In theory there could be 2 populations, a slow population and a fast population, and the fast population continually donates people to the slow population via immigration to sustain it. The worry would be if some idea from the slow population infects the fast population and causes it to slow down.