Final answer:
The field mice population subject to predation by a predator that targets larger individuals will likely undergo directional selection, leading to an increased prevalence of smaller body sizes. A histogram comparing pre and post predation would show a shift toward smaller sizes. Directional selection results in decreased genetic variance for the selected trait.
Step-by-step explanation:
When a new predator that easily captures larger-bodied field mice invades a habitat, the population of field mice is expected to undergo directional selection. Since the predator prefers larger mice, smaller mice have a higher chance of survival and reproduction. Over time, the population will likely evolve the trait of smaller body size, which will be depicted as a shift towards the left (smaller sizes) on a histogram of body sizes. A histogram would show the original population distribution with a range of sizes, and the new population distribution with more smaller sized individuals and fewer larger ones.Here is a hypothetical histogram representation:The x-axis represents body sizes.The y-axis represents the number of individuals.
The first plot line shows a normal distribution of body sizes (before the predator's arrival).The second plot line shows a leftward skew in body sizes (after the predator's influence).This shift is a result of directional selection, where one extreme of a trait provides a survival advantage and becomes more common in the population. Unlike stabilizing selection, which favors the average phenotype, or disruptive selection, which favors both extremes of the phenotype, directional selection favors one extreme. This results in a decrease in the genetic variance for the trait under selection, as the allele frequencies in the population change.