Which factors are classified as postzygotic isolating mechanisms?

Postzygotic isolating mechanisms are factors that occur after fertilization and affect the viability or reproductive capability of the hybrid offspring. Hybrid sterility, as indicated in the correct answer, specifically refers to a situation where the hybrid offspring resulting from the mating of two different species are sterile and, therefore, unable to reproduce. This prevents the exchange of genes between the parent species, effectively maintaining distinct species boundaries.

In contrast, the other options pertain to prezygotic isolating mechanisms, which occur before fertilization and prevent mating or fertilization from taking place. Behavioral barriers involve differences in mating rituals or behaviors that prevent different species from recognizing each other as potential mates. Temporal barriers are related to differences in breeding seasons or times of activity, ensuring that species do not interbreed. Geographic barriers refer to physical separations, such as mountains or rivers, that prevent populations from coming into contact. These mechanisms play a crucial role in speciation by ensuring that species remain distinct and do not hybridize.