Birth Rate
Birth rate is the most important cultural growth factor. Cultivars with low birth rates are virtual non-players in the game of civilization and can largely be ignored by your culture once you have addressed any bleed they may cause.
For more reading on this topic, dive into “K vs. r Selection in Cultivars’ Birth Rates” on page 724 of the Appendix (or the earlier recommended “Why are Birth Rates Falling” on page 671 of the Appendix).