Answer:
The graph D is the correct option.
Explanation:
In ecological studies, directional selection can be described as the event in which a single phenotype is favoured through the process of natural selection. Due to this, the allele frequency of the population shifts towards the particular extreme phenotype with time.
The Graph D shows how the population of gerbile was before and how directional selection favoured a single phenotype and caused it to become abundant.
