What mode of natural selection favors individuals at one extreme of a phenotype range?

The mode of natural selection that favors individuals at one extreme of a phenotype range is directional selection. This form of selection occurs when environmental pressures favor a phenotype that is either at one end or one extreme of the phenotypic spectrum, leading to a shift in the overall population traits toward that extreme.

For example, if a population of birds has a varying beak size and the environment changes such that only the individuals with larger beaks can effectively access food, those birds with larger beaks will have a higher survival rate and reproductive success. Over time, this results in an increase in the frequency of larger beak sizes within the population.

This mechanism of selection contrasts with stabilizing selection, which favors intermediate phenotypes and reduces variation, and disruptive selection, which favors extreme values at both ends of the phenotype range. Sexual selection refers to the selection for traits that enhance mating success, which does not specifically align with favoring one extreme in phenotypes for survival.