Changes in Ecosystems:Ecological Succession

What is Ecological Succession?

• A series of predictable changes that occur in a community over time due to events in the environment.

• The changes may happen suddenly or very slowly.

Primary Succession

• The series of changes that occur in an area where no ecosystem previously existed

Primary Succession

• Glacier retreat: An area of rock uncovered by a melting ice sheet

• New island formed by the eruption of an undersea volcano

• Side of volcano

First, lichensthat do not need soil to survive grow

on rocks

Lichens break down rock to form soil.

A combination of

fungus and algae

Primary Succession

• Soil starts to form as lichens and the forces of weather and erosion help break down rocks into smaller pieces

• When lichens die, they decompose, adding small amounts of organic matter to the rock to make soil

Primary Succession

• The first species to populate an area are the pioneer species.

• They break up rock and begin soil formation.

Primary Succession

• Simple plants like mosses and ferns can grow in the new soil

Primary Succession

• The simple plants die, adding more organic material (nutrients to the soil)

• The soil layer thickens, and grasses, wildflowers, and other plants begin to take over

Primary Succession

• These plants die, and they add more nutrients to the soil

• Shrubs and trees can survive now

Primary Succession

• Insects, small birds, and mammals have begun to move into the area

• What was once bare rock, now supports a variety of life

Larger plants with deep roots continue to break up rock and make more soil.A diverse forest ecosystem takes hundreds of years

1. Ground is solid rock

2. Rock begins to weather, pioneer species begin

3. Weeds and grasses grow in soil -making thicker, richer soil

4. Eventually trees and shrubs sprout - community of organisms develops

Stages of Primary Succession

Secondary Succession

• Begins in a place that already has soil and was once the home of living organisms – Example: after forest fires

• Occurs faster than primary succession

Human disturbances:•A pasture abandoned by a farmer•Logging, or mining

Examples of Secondary Succession

Natural disturbances:

Fires, hurricanes, and tornadoes

1. Varies depending on the type of disturbance

2. A disturbed area returns to its previous condition

3. Soil and seeds are already present

4. Organisms move in

5. There is a quick recovery of the ecosystem

Stages of Secondary Succession

Climax Community

• A stable group of plants and animals that is the end result of the succession process

• Does not always mean big trees

–Grasses in prairies

–Cacti in deserts

A Succession Review

Primary Secondary

What

happens to

the

ecosystem

Length of

Time

Example

Creates a new ecosystem

Restores a previous

ecosystem

May take a long time to reach equilibrium

A shorter time to reach equilibrium

New land created by volcanic eruption

An area destroyed by fire