Final answer:
The varying courtship songs among cricket populations act as a prezygotic isolating mechanism, preventing interbreeding and maintaining species boundaries by ensuring females preferentially mate with males of their own population.
Step-by-step explanation:
The difference in courtship songs among the three populations of crickets serves as a prezygotic isolating mechanism. This type of isolating mechanism occurs before the fertilization process and ensures that mating and therefore gene exchange between the different populations does not happen. In the case of courtship songs, females are likely to prefer the songs of their own population's males, reducing the chance of mating with males from other populations with different songs.
Other examples of prezygotic barriers include temporal isolation, where species reproduce in different seasons; or habitat isolation, where populations are physically separated. Gametic barriers also exist when egg and sperm cells from different species are unable to fuse. All these mechanisms prevent the formation of a zygote and maintain species integrity.