Hi, the two species were usually recognized a competitors to some degree. There was a long history of Norway rat pushing back the Rattus rattus. However, in recent years, there are some news about regaining some territories by Black rat.  It seems possible, that one way of adaptation of the two species is the increase of mutual tolerance of the two species. They would have to work out however, the way to share the niche, or to avoid confrontation.

I have studied nest sites of black rats in the wild and we never found them associated with nest sites of Rattus Rattus though both species were in the same area, plus smaller differences of preferred sites of the two, and  in the two and  the diet  preferred the two species argues against this possibility.  One major difference in the two is a greater preference ifor climbing in black rats.  At least this was true in Hawaii.

Thanks for your answer Ernest