At a guess I’d say wolves.
Not much else changed except the eradication of the Mooses traditional antagonist .
Map seems to indicate southerly movement down Idaho to Wyoming Yellowstone( take that as a loose suggestion).
Moose don't compete with Bison which are plains, grassland foragers. Moose found more in wetlands, lakes, marshes, slow moving streams, etc., within forests. I've only seen one moose and that was in Maine forest. Awesome.