Which of the following prevents mating or fertilization?

Behavioral isolation is a mechanism that prevents mating between species by differing behaviors or mating rituals. In many species, particularly those that have intricate mating calls, displays, or rituals, individuals may not recognize or be attracted to the mating cues of potential partners from other species. This lack of recognition leads to the prevention of mating altogether, as individuals will not engage in courtship behaviors necessary for reproduction.

In contrast, while hybrid sterility, post-zygotic barriers, and gamete isolation also play roles in reproductive isolation, they function at different stages of the reproductive process. Hybrid sterility occurs after mating has taken place but results in offspring that are unable to reproduce. Post-zygotic barriers include any mechanism that reduces the viability or reproductive success of hybrid offspring after fertilization has occurred. Gamete isolation prevents fertilization by ensuring that the gametes (sperm and egg) from different species are incompatible, but it does not encompass the behavioral component that leads to mating itself.

Thus, through its focus on the behaviors that either facilitate or hinder mating interactions, behavioral isolation stands out as the factor that directly prevents mating or fertilization.