What situation occurs when members of two different species cannot interbreed and produce fertile off-springs?

Reproductive isolation occurs when members of two different species cannot interbreed and produce fertile offspring. This can be due to a number of factors, including:

* Geographic isolation: This occurs when two species live in different geographic areas and are unable to meet and mate.

* Ecological isolation: This occurs when two species live in the same geographic area but occupy different habitats or have different mating seasons.

* Behavioral isolation: This occurs when two species have different courtship rituals or mating behaviors.

* Mechanical isolation: This occurs when the physical structures of two species are not compatible for mating.

* Gametic isolation: This occurs when the gametes (eggs and sperm) of two species are not compatible and cannot fertilize each other.

Reproductive isolation is an important factor in speciation, the process by which new species are formed. When two species are reproductively isolated, they are unable to exchange genes and evolve together. Over time, this can lead to the development of two distinct species.