Why is variations beneficial to the species but not necessary to individuals

Variations are beneficial for the survival of the species. Populations of organisms fill well-defined places, or niches, in the ecosystem, using their ability to reproduce.However, if some variations were to be present in a few individuals in these populations, there would be some chance for them to survive.

I think the answer is B.) area a has more predators than area b but it could be D since we are talking about space/ carrying capacity