Definition of Ecological Succession

The series of predictable changes that occur in a community over time.

Primary succession

The first step in primary succession is the formation of soil.

(Generally slow, many 1000s of years)

• ​Usually occurs in an area that previously did not support life

• Much slower than secondary succession

Causes of Primary Succession

1.

Volcanic eruptions

2. When glaciers expose
bare rock

Pioneer Species

• First species to colonize bare rock
• Help break up rocks and form soil, so other species can grow.

As soil is formed, plant seeds blown in from other areas will take root

Lichens

• Lichens are one important group of pioneer species.

• A lichen represents a mutualistic symbiosis.

• Lichens are composed of a fungus and a

photosynthetic organism (algae or bacteria).

How do lichens help with primary succession?

1.

Secrete acids that help break down rocks

2.

When they die, lichens add organic material to the soil

3. Provide food for other organisms

Secondary Succession

• Occurs when a disturbance changes the existing community

• The soil is not removed

Disturbances that can initiate secondary succession:

• Fire
• Agriculture
• Hurricanes

Over time, the plant community changes.

Rock

Pioneer species →

Small plants/grasses → ↓

←Shrubs/bushes

←Small trees

←Larger trees

​Climax Forest

Succession in a Marine

Environment

Whale-fall Community

Very difficult to study!

3 Stages

1.

Whale dies and sinks to ocean floor and attracts decomposers and scavengers

2. Once the tissues are gone, the carcass supports a smaller set of organisms. 

- decomposition enriches the sediments

3. When only the skeleton remains, bacteria begin to decompose the bones.