Ecosystem Responses to Disturbance

1. Ecosystem Responses to Disturbance • Ecological succession • Disturbance and resilience • Evolving ecosystems

2. Equilibrium Theory • Ecosystems are stable environments in which the biotic interactions among species determine the structure of the communities present.

3. Succession and Disturbance • Ecological succession: transition between biotic communities • Primary: no previous biotic community • Secondary: previously occupied by a community • Aquatic: transition from pond or lake to terrestrial community

4. Primary Succession • Mosses invade an area and provide a place for soil to accumulate. • Larger plants germinate in the new soil layer, resulting in additional soil formation. • Eventually shrubs and trees will invade the area.

5. Primary Succession

6. Secondary Succession • Soil present • Most of the biotic community destroyed • Human development • Landslides • Fire

7. Secondary Succession • Growth of Climax Ecosystem limited • Erosion of soil • Drought • High temperature

8. Secondary Succession

9. Aquatic Succession • Fresh water aquatic ecosystem develops into a terrestrial ecosystem • Sediment and detritus fills in pond or lake • Amount of water decrease • Meadow is often a transitional stage • Climax community  bog or forest

10. Aquatic Succession

14. Disturbance and Resilience • Removes organisms • Reduces populations • Creates opportunities for other species to colonize

15. Ground Fire

16. Fire and Succession • Fire climax ecosystems: dependent upon fire for maintenance of existing balance; e.g., grasslands, pine and redwood forests • Forest management necessary • Burn off brush and debris on forest floor • Germination of new trees • Reintroduce nutrients into soil