Final answer:
When males produce more sperm to increase their chances of fertilizing an egg due to competition with other males' sperm, this is known as sperm competition, which is a form of sexual selection.
Step-by-step explanation:
If a male that produces a greater quantity of sperm sires more offspring, the mechanism of sexual selection involved is c. sperm competition. This concept defines a scenario where multiple males may compete post-mating by producing more sperm, which may increase their chances of fertilizing an egg in species where females may mate with more than one male.
The phenomenon of sperm competition is distinct from other forms of sexual selection like male-male combat or female choice, and it relates more closely to the efficiency and strategic allocation of one's reproductive resources.