Two species of salamanders, Plethodon cinereus and Plethodon hoffmani, overlap in parts of their range in the eastern United States. The two species are very similar in size except in places where both species are found. In places where both species are found, Plethodon cinereus is smaller than it usually is, and Plethodon hoffmani is larger than it usually is. This size difference is related to what the salamanders eat: Plethodon cinereus eats smaller prey than it eats in other parts of its range, and Plethodon hoffmani eats larger prey than it eats in other parts of its range. How can natural selection due to interspecific competition explain the evolution of size and diet in these salamanders?