Just thought I'd share this as I found it interesting...
I've had a 75g tank very lightly stocked for a couple of years now (1 clown, 1 YT and 1 Skunkback Pseudochromis. That whole time the skunkback was boss (and he knew it too), he was always knocking hermits, snails, etc off the rocks and glass. If something moved he was right there to show it who was boss. That is until recently....
I added a Foxface about a month or so ago and the skunkback will have nothing to do with him. If the Foxface is in the front, the skunkback is in back and likewise opposite ends of the tank. The foxface follows the YT wherever he goes and sometimes the YT is not too excited about that and lets him know with the flick of his tail, but thats another story.
Anyway, just by adding the Foxface (who wouldn't hurt a flea) it has changed the entire dynamic of my tank.
Makes me wonder what the next addition will do....