how do rabbits and foxes depend on each other in a forest habitat

Answer 1

Foxes eat rabbits, so, without rabbits foxes will be hungry and have to seek other prey. Possibly the fox population would decline in the absence of rabbits.

Classically, it has been thought that predators (foxes in this case) keeps prey (rabbits in this case) populations strong by removing weaker individuals. Without foxes, rabbit population would grow uncontrolled and exceed carrying capacity.