Answer: to explain what keystone species are important in each ecosystem
Explanation:
The overall theme of the article is to explain what keystone species are important in each ecosystem.
Keystone species is referred to as an organism that defines the ecosystem as a whole. They help define the habitat's biodiversity.
It should be noted that despite the fact that every living organisms depends on each other, some species are more vital than others and when they're removed, there will be a drastic change in the habitat.