How do I control ant, rat and pig people's population?

These three races live in burrows. Their population panel does not expose the bed-dwelling one/two-child threshold controls. Set each burrow's maximum occupancy and its forbid-birth switch. Initial occupancy is 20, but it is not an absolute birth cap: a burrow family's first child bypasses the crowding check; subsequent births check available space. More than 20 residents can therefore occur.