Afraid for an exotic?

When becomes an exotic species a thread to inland species?
They studied fish. How can you see IF an exotic can become a species that will bring your own inland species to extinction? When eating structures (jaws, intestine,...), and also the food they eat, looks more and more like the inland species the more chance they drive the inland species to extinction!
https://www.naturetoday.com/intl/nl/nat ... ?msg=24415
http://journals.plos.org/plosone/articl ... ne.0197636
http://journals.plos.org/plosone/articl ... =printable
Are there any studies like that but about ants?
They studied fish. How can you see IF an exotic can become a species that will bring your own inland species to extinction? When eating structures (jaws, intestine,...), and also the food they eat, looks more and more like the inland species the more chance they drive the inland species to extinction!
https://www.naturetoday.com/intl/nl/nat ... ?msg=24415
http://journals.plos.org/plosone/articl ... ne.0197636
http://journals.plos.org/plosone/articl ... =printable
Are there any studies like that but about ants?