In this topic you will learn about how a change in an ecosystem affects the organisms that live there.

Ecosystems can change. When change occurs, the organisms that live in the ecosystem are affected. Some have trouble surviving. Before the spring of 1980, Mount St. Helens was a sleeping volcano. Then, on May 18, 1980, Mount St. Helens erupted. A huge eruption changed local habitats forever. After the eruption, the forest was buried in ash. When it rained, the ash turned muddy. Then the ash hardened into a tough crust. Plants were killed. Habitats were destroyed. A wind of hot steam and rock blasted the area. Animals that roamed the forest also lost their habitats.

A volcanic eruption is one event that can change an ecosystem. Floods, droughts, fires, earthquakes, and storms can also change an ecosystem. After a big change, ecosystems usually come back.

Organisms may respond to change in one of three ways. Some organisms respond by adapting. Adapting means adjusting to a new habitat. Fireweed on Mount St. Helens adapted by growing through the crust. Some organisms perish. Organisms that perish do not survive. A turtle may survive a fire. If it cannot meet its needs after the fire, it may not survive. Some organisms relocate. An organism that relocates finds a new home. Birds that lived in trees on Mount St. Helens could fly to other trees.

Habitat destruction and overcrowding are not the only threats to organisms. Other threats include hunting and pollution. In some cases organisms become endangered. An endangered organism is one that has very few of its kind still alive. Endangered organisms may become extinct. Extinct means that there are no more of that type of organism alive. Extinct animals include the dodo bird and the saber-toothed tiger.