That's why I keep only the ants I can found in my city or its surroudings. I know at least 15 species living in Krakow, so there is a lot to choose from. Of course some of them are quite rare, but this makes queen hunting more exciting
Ant species slowly change their territories in natural ways along with the environment changes. Southern species like Messor or Pheidole will migrate north due to climate warming. Some local ants like Manica rubida, living naturally in mountains, take opportunity to settle in cities, also full of sunny places and rocks. Species extinct in some countries due to ecological devastation, like Camponotus in UK can be re-introduced naturally if the environment improves. There is no need to interfere with this process and help them. The migrating populations usually take their natural enemies with them, and so the local fauna changes but doesn't lose it's diversity. Species introduced by humans from other continents, which otherwise have no chances to migrate naturally, are usually most dangerous.