Final answer:
The scenario with alpha male elephant seals is an example of diversifying selection, a form of natural selection where two extremes of phenotypes have advantages over intermediate phenotypes, leading to increased genetic variance and population diversity over time.
Correct option is a) Sexual dimorphism.\
Step-by-step explanation:
The alpha male elephant seal fending off medium-sized males while small males sneak copulation is an example of diversifying selection. This biological concept refers to a scenario where two or more distinct phenotypes have advantages for natural selection, while intermediate phenotypes are less fit. In our case, large dominant alpha males monopolize mates due to their size and strength, while small males succeed by using sneaky tactics to copulate. Both extremes have distinct reproductive advantages, leading to a higher reproductive success for these males, but not for males of medium size, who lack the brute force of large males and the ability to sneak mating like small males.
This example fits into the broader topic of sexual selection, which is a mechanism of evolutionary change and adaptation. The phenomenon described illustrates how selective pressures can lead to an increased genetic variance in the population, making it more diverse over time.