Are Keystone species always predators?

What is a keystone species?

• What are a couple of species that are considered and keystone species?

• Answer:

  Andrew O's definition is a very good one. One classic example involves a species of starfish. In the 1960s, a researcher named Dr. Roger Paine removed all the specimens of one species of starfish (Pisaster spp.) from coastal tidepools in Washington to see what would happen. When the starfish was removed, the species of mussels it normally fed on no longer had a predator, and spread out of control. As a result, many other species vanished from the tidepools. Removing just this one species of starfish reduced the biodiversity (variety of species) in the tidepools by more than 50 percent. Another classic example happened unintentionally. Sea otter populations once stretched along the entire Pacific Rim from Japan to Southern California. In the 1800s, sea otters were wiped out through most of their southern range in the US due to hunting for the fur trade. Sea otters love to eat sea urchins. When the sea otters vanished, the sea urchins lost one of their biggest predators and spread out of control. Sea urchins, in turn, feed on kelp; and without the sea otters to control their numbers, the sea urchins eventually destroyed the vast kelp beds off the California coast. The kelp provided habitat for many species, so when the kelp disappeared, so did these species. Vast stretches of the coast were turned into relatively lifeless areas called "urchin barrens"--all because the sea otters were gone. As sea otters returned to the Pacific coast decades later, urchin populations declined again, kelp beds began to recover, and species started coming back. The concept of keystone species becomes particularly important as populations of top ocean predators like sharks decline. With sharks and other top level predators vanishing,the mid-level predators they feed on may be expanding, with potentially very damaging impacts on ecosystems.