Final answer:
A keystone species has a large impact on an ecosystem compared to its abundance, while an umbrella species indirectly helps protect other species by protecting its own habitat.
Step-by-step explanation:
A keystone species is one whose presence is key to maintaining biodiversity within an ecosystem and upholding an ecological community's structure. These species have a disproportionately large impact on the ecosystem compared to their abundance. For example, the intertidal sea star Pisaster ochraceus is a keystone species because when it is removed from communities, mussel populations increase, altering the species composition and reducing biodiversity.
On the other hand, an umbrella species is a species that, if protected, indirectly helps to protect the numerous other species that share its habitat. By focusing conservation efforts on the umbrella species, we can protect its habitat and indirectly protect other species. For example, protecting the habitat of the African elephant also benefits other species that depend on the same ecosystem.