Ecological Succession

Biology 1-2

Ecological Succession

Ecological succession-process of biological community change. Usually the result of a disturbance. Also occurs when a new area opens up. Succession is how an area recovers after the

disturbance.

Succession cont’d

During succession . . . Species makeup changes quickly at first. Size of the organisms increases. Diversity increases, then stabilizes. Switch from r-selected to K-selected species. Each community changes the environment,

allowing succeeding communities to replace them.

Primary Succession

Primary succession-area is initially barren and lifeless. No soil is present. Occurs following volcanic eruptions or glacier

retreat.

Primary Succession cont’d

The first stage of succession is called the pioneer stage. The first organisms are lichens and mosses.

Wind carries spores to the new area. Can tolerate environments most organisms cannot. Reproduce rapidly to overcome losses. Prepare the area by breaking down rocks to create soil. Make the environment suitable to others.

Primary Succession cont’d

After the pioneer stage are the intermediate stages. Intermediate communities follow the pioneers. Grasses and shrubs, followed by small trees and

bushes. Small mammals, birds, insects and reptiles move

in.

Primary Succession cont’d

The intermediate stages lead to the climax stage. The climax community is the last community to

appear. Will not change unless disturbed. Characterized by tall trees and more complex

interactions in the community.

Primary Succession cont’d

The climax community forms and maintains equilibrium. K-selected species replace many r-selected species. Competition, predation and symbiosis become

more extensive. All niches are filled.

Secondary Succession

Secondary succession The area is cleared out but the soil is left intact. Occurs following fires, floods, human activity, etc. Follows the same pattern as primary succession

(pioneer to intermediate to climax). The pioneer community is weeds and grasses. Secondary succession is faster than primary

succession. Lichens and mosses are not needed to create soil.

Disturbances and Recovery

Some communities are adapted to periodic disturbances. San Diego is a chaparral community.

Fire climax community. Fire clears out dead material and old growth, making

way for new growth. Many native plants have adaptations for surviving.

Community recovers and reaches the climax stage quickly.

Disturbances cont’d

Fire prevents a more traditional climax community from forming. Fire kills saplings and the seeds of trees that would

replace the local shrubs. Trees lack adaptations to survive in the

environment. A traditional climax community is unstable and more

open to change.