Final answer:
Pre-zygotic barriers are mechanisms that prevent reproduction before the formation of a zygote. Examples include gametic isolation and mechanical incompatibility, which hinder fertilization and mating between closely related organisms.
Step-by-step explanation:
Pre-zygotic barriers are mechanisms that prevent reproduction from taking place, specifically before the formation of a zygote. One example of a pre-zygotic barrier is gametic isolation, where differences in gamete cells (eggs and sperm) prevent fertilization. Another example is mechanical incompatibility, where closely related organisms have reproductive structures that do not fit together. For instance, damselfly males of different species have differently shaped reproductive organs, making it impossible for them to mate with females of other species.