Keystone Species
People don't always understand the interconnections in an ecosystem. If an animal is considered a particular pest, we often try to get rid of it. Sometimes this can upset whole ecosystems and make things a lot worse. This is especially true if the animal is a keystone species.
Alligators Protect Game Fish
Did you know that when the American alligator became endangered from over-hunting, all the fish started to disappear? That was because alligators eat a large fish called a gar, which feeds on many kinds of game fish. When the alligators disappeared, the gar populations exploded and they ate all the fish! Not until the alligator was protected and began to recover did the gar populations come under control so the other fish species could come back, too.
An example of people altering an entire ecosystem involved a little mammal on the California coast — the sea otter. They were hunted for their fur almost to extinction in the 1700–1800s. Then fishermen began to see changes in the ecosystem without the sea otter. Sea otters are one of the few animals that eat sea urchins. When the otters disappeared, the sea urchin population grew rapidly. Sea urchins, in turn, feed on kelp. The kelp beds are also very important to several fish populations as a place to spawn. So with the otters gone and the sea urchins on the rise, the kelp beds began to disappear too. Then the fish, having lost their spawning site, disappeared as well. Suddenly, in just a few years, the fishermen found that the fish were gone.
Then, in 1911, a treaty was passed that protected sea otters from hunting (the International Fur Seal Treaty). In the areas where sea otter numbers recovered, the sea urchin populations were brought back under control. Then the kelp beds recovered and the fish populations came back too. This is an example of how a keystone species is interconnected with a whole ecosystem.
