When rodents enter the picture, they eat large seeds, favoring the growth of small seeds, which make plants producing more small seeds, which ants eat. When rodents are removed, the large-seeded plants recover in number, competing with and reducing numbers of small-seeded plants, which in turn gives less food for ants and fewer ant colonies.
Work Step by Step
The key is the connection between ants and different seed sizes. Basically, this question asks you to see the way that many organisms affect one another's populations.