Final answer:
Reduced hybrid fertility is a postzygotic barrier that prevents hybrids from reproducing, not a prezygotic barrier. Prezygotic barriers like habitat isolation, behavioral isolation, and temporal isolation prevent fertilization from taking place. Therefore, the correct option is a.
Step-by-step explanation:
The question is asking us to identify which option is not a prezygotic barrier. Prezygotic barriers are mechanisms that prevent reproduction from occurring; they include factors like habitat isolation, behavioral isolation, and temporal isolation. These prevent fertilization when different species attempt to reproduce. On the contrary, reduced hybrid fertility is a postzygotic barrier, which means it occurs after the zygote has been formed. It refers to the offspring (hybrids) being infertile, thus unable to reproduce. Given the options, the correct answer is "a. Reduced hybrid fertility," as it is not a prezygotic barrier, but rather a postzygotic one.