Moose and wolves have been studied on Isle Royale for 50 years now. It is of great scientific interest because the number of variables affecting predator and prey are much smaller than on the mainland (Isle Royale is a large island in Lake Superior, and a national park). Wolves are the only large predator and moose are they prey, and the populations of each have gone up and down many times of the fifty years. They do not move in in exact concert.
Now unusually warm summers have increased the tick population that debilitates moose in the winter on the island (and pretty much whereever moose live). Moose numbers are declining due to their weakness, and the wolves are getting hard pressed for food with interpack strife and they are declining in numbers too.
There are fox on Isle Royale too, and they are suffering as well.
I can’t help but hypothesize that some elements of this are present in the elk number decline and wolf number decline on the northern range of Yellowstone.
Story from the International Wolf Center. Slim Pickings for Wolves on Isle Royale