What would happen to a population of rabbits if the number of foxes, a predator of rabbits, increased?
Assuming no other ecosystem changes, the rabbit population will (likely) decrease.
For the fox population to increase there must be an increase in their food supply.
If all other populations remain stable, then this increase must be in the form of rabbits.
The qualifier in my Answer ("likely") is based on the possibility that the rabbit population was at its maximum sustainable value, in which case an increase in rabbit deaths due to foxes might only offset deaths from other causes (e.g. starvation).