The ecosystem will more stable. The mating with unrelated specie will create the ability to cop with any disaster and the chances of extinction of any specie will become very less.
Less stable.
An ecosystem which has a very low number of species ins not so stable because of less biodiversity. Biodiversity is directly proportional to the stability of the specie.
Less stable.
The specie which does not have the ability to mate with unrelated specie makes an unstable ecosystem. Because if any thing happens to the ecosystem like climate change, that specie will unable to evolve and go extinct immediately.
More stable:
The ecosystem having a large number of biodiversity at each trophic level leads to a stable an ecosystem. Because biodiversity is directly proportional to the stability of the specie.