A population of beetles is composed of three color variants: dark, light, and medium tan colored beetles. Initially, the beetles inhabit a field environment in which the vegetation is mostly a medium tan color.
This environment is favorable for the medium tan colored beetles as it masks them from their predators, making it difficult for them to be preyed upon.
After the turn of the 20th century, a paper mill is built at the edge of the field that produces a great deal of pollution, causing the surrounding environment to become darker in color.
Which of the following diagrams BEST illustrates the change in the population that occurs after the paper mill was built?