Final answer:
Stabilizing selection results in reduced variation, directional selection shifts phenotype distribution, and disruptive selection increases genetic variance by favoring extreme phenotypes. The specific type of selection on the graph cannot be determined without seeing the graph.
Step-by-step explanation:
The question is asking to identify the type of natural selection represented by a given scenario on a graph. There are three main types of natural selection: stabilizing selection, directional selection, and disruptive selection. Without the graph, I cannot provide a specific answer to the timed question regarding which type of selection is shown, but I can explain each type for understanding.
Stabilizing selection occurs when the average phenotype is favored over the extremes, resulting in reduced variation and maintaining the status quo. An example of stabilizing selection is the human birth weight where both very large and very small babies have lower survival rates, hence the birth weight is kept within a narrow range.
Directional selection occurs when environmental changes or other factors cause one extreme of a trait to be favored over the other, which can lead to a shift in the phenotype distribution over time. An example is the increase in dark-colored moths after the Industrial Revolution because they were better camouflaged against predators.
Disruptive selection, also known as diversifying selection, occurs when extreme phenotypes are favored and intermediate phenotypes are selected against. This can lead to increased genetic variance and can result in two distinct phenotypes within the population, such as sexual dimorphism.