<P> Genetic diversity plays an important role in the survival and adaptability of a species . When a population's habitat changes, the population may have to adapt to survive; the ability of the population to adapt to the changing environment will determine their ability to cope with an environmental challenge . Variation in the populations gene pool allows natural selection to act upon traits that allow the population to adapt to changing environments . The more genetic diversity a population has, the more likelihood the population will be able to adapt . </P> <P> Genetic diversity is essential for a species to evolve . With very little genetic diversity within the species, healthy reproduction becomes increasingly difficult, and offspring are more likely to have problems resulting from inbreeding . The vulnerability of a population to certain types of diseases can also increase with reduction in genetic diversity . Concerns about genetic diversity are especially important with large mammals due to their small population size and high levels of human - caused population effects . </P> <P> When humans initially started farming, they used selective breeding to pass on desirable traits of the crops while omitting the undesirable ones . Selective breeding leads to monocultures: entire farms of nearly genetically identical plants . Little to no genetic diversity makes crops extremely susceptible to widespread disease; bacteria morph and change constantly and when a disease - causing bacterium changes to attack a specific genetic variation, it can easily wipe out vast quantities of the species . If the genetic variation that the bacterium is best at attacking happens to be that which humans have selectively bred to use for harvest, the entire crop will be wiped out . </P> <P> A very similar occurrence is the cause of the infamous Potato Famine in Ireland . Since new potato plants do not come as a result of reproduction, but rather from pieces of the parent plant, no genetic diversity is developed, and the entire crop is essentially a clone of one potato, it is especially susceptible to an epidemic . In the 1840s, much of Ireland's population depended on potatoes for food . They planted namely the "lumper" variety of potato, which was susceptible to a rot - causing oomycete called Phytophthora infestans . This oomycete destroyed the vast majority of the potato crop, and left one million people to starve to death . </P>

When do we say that genetic diversity is helpful in an ecosystem