As far as I know pops do not move on their own anymore. You have immigration/emigration modifiers that slow or increase growth. To move pops you have to resettle.
I believe the adaptability tradition lowers resettle cost by 33%.
Interestingly, if you start with 3-4 colonies off the bat you'll notice pop growth in your home-world slows to a crawl. This is because of all the emigration pull. Colonies themselves have -50% modifier so while the immigration helps it continues to be slow and inefficient for those early years.