Two similar rodent species are consistently more different from each other when they occupy the same habitat than when they live separately. What is the most likely explanation for the increased divergence when they live together

Character displacement & Evolution by natural selection

Explanation:

Character displacement is the name used to illustrate an evolutionary change that happens when two related or similar species inhabit the same environment. Under this type of conditions, natural selection supports a divergence in the characters--morphology, behavior, ecology, or physiology--of the living organisms.

While natural selection refers to the differential survival and reproduction of species in an environment due to differences in phenotype. It is a vital mechanism of evolution, the change in the genetic traits and characteristic of a population over several generations.