The very reason there are so many species of shiners is due to their different abilities. Each has a specific niche they are suited to fill, no two fill the same niche exactly the same way. One will always be the best at proliferation in a certain environment that the others aren't quite great at. So to answer the question... if the system is closed and only one species is introduced it may or may not be able to take over that niche. If all the possible species were introduced at the same time they'd fill all suitable niches with only the best suited one taking over any certain niche. Hope that made sense.

19 acre watershed pond
LMB, BC/WC, Bluegill, Crawfish, GShiners