Without the kelp forests, all of the fish, snails, crabs, and birds would no longer have a source of food and protection, causing their numbers to be severely negatively impacted. It is for this reason that the sea otters are considered to be a keystone species in the Pacific Northwest. Without the otters to control the sea urchin population, the kelp forests would be consumed and the habitat for many other species would disappear, leading to a significant decline in their numbers.
The elephants in the Serengeti plains of Tanzania are a unique keystone species due to the fact that they are a herbivore, whereas many keystone species are omnivores or carnivores. The elephants feed predominantly on small trees called Acacia trees. These trees are usually no higher than a few feet, allowing the elephants to easily feed on the trees and even uproot them in order to eat them. Because elephants consume such a large number of these trees, the trees are rarely ever able to grow to large sizes