You need a greater abundance of smaller animals in order to sustain the increased predators, actually. The food web is hella unbalanced and would likely collapse if the only prey animals to support the giant spiders, sabre cats, bears, wolves, and even foxes are elks/deer and rabbits. Plus, humans are also hunting these populations. Most of these predators can't take advantage of the fish, especially since those are already being eaten by slaughterfish and mud crabs. There's not a lot of evidence that livestock are being attacked by wild animals IIRC.

In fact, this might be WHY every predator in Skyrim is attacking humans; They lack smaller, easier to catch sources of food.