4.C.4 Ecosystem Stability The diversity of species within an ecosystem may influence the stability of the ecosystem.

Natural and artificial ecosystems with fewer component parts and with little diversity among the parts are often less resilient to changes in the environment.

Keystone species, producers, and essential abiotic and biotic factors, contribute to maintaining the diversity of an ecosystem.

The effects of keystone species on the ecosystem are disproportionate relative to their abundance in the ecosystem. When they are removed from the ecosystem, the ecosystem often collapses. Keystone Species Enhances habitats Regulates populations Pollination Removes genetic weakness Recycles nutrients and wastes

The term keystone species was first coined by Robert Paine in 1966, who studied the effects of the artificial removal of the starfish Pisaster ochraceus from an intertidal ecosystem.

Paine found that removal of the predator species Pisaster reduced the number of other species occupying the ecosystem from 15 to 8 within a single year.

Gray Wolves: A Case Study of Keystone Species Removal and Restoration

Gray wolves (Canis lupus) once roamed the western portions of North America from Alaska to Mexico.

During the latter 19 th century, the wolf’s prey, mostly bison, elk, deer, and moose, were severely overhunted. The wolves adapted to preying upon livestock, angering farmers and ranchers.

The federal government began eradicating the wolf population. Bounty programs offered as much as $50 per wolf. By the 1930s wolves had been hunted, poisoned, and trapped to extinction everywhere in the lower 48 states.

With the wolf gone, elk populations rapidly exploded, resulting in overgrazing and significant declines in many plant species such as aspen and willow. This in turn reduced the beaver and songbird populations.

The disappearance of the affected plant species led to the loss of habitat for many other species and resulted in other ecological disturbances such as the weakening of stream bank stability, the warming of water temperatures caused by loss of shading foliage, and disturbing nutrient cycling throughout whole ecosystems.

In 1995, the federal government began reintroducing gray wolves back into Yellowstone National Park. Their numbers have swelled, alarming ranchers and farmers in Montana and Wyoming.

Today, the Gray Wolf’s future is once more uncertain. The US Fish and Wildlife Service has taken them off the endangered species list, allowing some states to establish a wolf hunting season once again.

Learning Objectives: LO 4.27 The student is able to make scientific claims and predictions about how species diversity within an ecosystem influences ecosystem stability. [See SP 6.4]

Credits brary/keystone-species