There are other possible hypotheses. There could be some predator on ants which were more or less likely to come into the habitat based on rodents being present. The thing to do in testing this is to experiment by removing any putative factor to explain the data and comparing the result with the results in Fig. 56.22 to determine if that other factor has an effect.
Work Step by Step
The way to test these interactions is to alter them by removing or by changing the number of one organism/factor and observing whether a change in experimental observations occurs. If there is a change, the putative factor has some role in the ecosystem interactions.