One way to describe a species is as a population adapted to a certain niche. that population has a small gene pool. if the members of different species could interbreed with each other, too much genetic variability would occur in that gene pool. too much genetic variability would

In determining species, it is best to differentiate in terms of the population that is being adapted in which, a certain niche. So, if it has a small gene pool, and the different species will be interbreeding each other with a much genetic variability in gene pool, it would most likely cause a less adaptation. The niche will be having a less adaptation if too much genetic variability will occur.