Many owls eat small rodents and similar critters. So let's say the rabbit population might grow if owls weren't there to keep the numbers down.
Foxes probably eat the same sort of small rodents. So if owls weren't there, foxes would have more food to themselves, so their population might go up.
And if foxes had more small rodents to eat, they would eat relatively less of any one species. So if they had plenty of rabbits to eat, they might eat less squirrels, so the squirrel population would go up.