Answer
You should either remove or alter the plants present to see if the effect of rodents on ants is removed. For example, you could artificially alter the number of small-seeded plants to try to disrupt this effect.
Work Step by Step
Since the plants serve as intermediaries, they are like gears between pedals and wheels in a bicycle. Remove a gear, and you see that the pedals no longer affect the wheels. This is analogous with altering numbers of one or the other kind of plant.
