What type of isolation would result if two species are physically separated by barriers?

Habitat isolation occurs when two species are separated by physical barriers that prevent them from interacting with one another. This can happen due to geographical features such as mountains, rivers, or other obstacles that create distinct environments for each species. When species do not share the same habitat, they are less likely to come into contact, mate, or exchange genetic material, ultimately leading to reproductive isolation over time.

In contrast, behavioral, mechanical, and gametic isolation refer to different mechanisms that prevent species from mating or producing viable offspring even when they are in proximity to one another. Behavioral isolation involves differences in mating behaviors or rituals, mechanical isolation refers to incompatible reproductive structures, and gametic isolation occurs when sperm and egg from different species cannot fuse. These types of isolation do not rely on physical barriers but rather on factors that affect mating and fertilization processes. Thus, habitat isolation is the appropriate answer in this context.