A keystone species is a species which affects the survival and abundance of many other species in the community/habitat in which it lives. Aardvarks are considered a keystone species by many people as many mammals and insects use their abandoned burrows for protection and shelter from the sun, predators and to bring up their young.
Another reason that aardvarks are important to their habitat is because a plant known as the aardvark cucumber relies on the long nosed mammal to spread it's seeds. The fruit grows underground and is a treat for any aardvark, but being underground it's very hard to spread it's seeds and germinate. Aardvarks help the plant to survive and flourish by eating the fruit and spreading their seeds in their dung.