Imаgine twо species оf snаkes thаt live in a trоpical rain forest of Malaysia do not typically interbreed. In nature, one species is ground-dwelling and feeds mainly on insects and small amphibians near water, whereas the other snake feeds in the lower to mid-canopy of trees and vines rising from the forest floor. However, at a zoo in Singapore where they were kept in the same gallery exhibit, the two species were observed interbreeding and produced viable offspring. Which of the following reproductive barriers is most likely preventing these species from interbreeding in the forest?