How are variations useful for species if there is drastic alteration in the niches?

Question: How are variations useful for species if there is drastic alteration in the niches?

The correct answer is :

If the niche were drastically altered, the population could be wiped out.
However, if some variations were to be present in a few individuals in these populations, there would be some chance for them to survive. Variation is thus useful for the survival of species over time.