Unit 4B Pt5

Caused by disturbances such as:

• Volcanos & lava flows

• Re-treating glacier

• Oil spills

• Landslides

Results in no soil or soil that cannot sustain life!

• Barren rock is covered by moss

• Pioneer species such as lichens and mosses form on rocks

• Lichen can break rock down and mosses decompose, helping create soil

• Grasses begin to grow

• Small shrubs and small organisms start to come in

• Larger trees and different types of organisms come in, when there is more diversity and the ecosystem is back in equilibrium it is a climax community

Caused by disturbances such as:

• Forest Fire

• Floods

• Hurricanes & Tornadoes

• Deforestation

• Abandoned farmer's field

  Remember: Soil is present before & after disturbance!

1. Annual plants come about

2. Followed by grasses and small plants

3. Shrubs, small trees, and small animals

4. Large trees, diverse animals

5. Climax community

Predicts that the highest biodiversity, or species richness will occur at levels of moderate disturbance

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​Intermediate Disturbance Hypothesis

• Scheduled hunting seasons

• Seasonal flooding or drought

These disturbances may have a great impact initially, but over time, might not impact the ecosystem very much.

Some scientists believe that these types of disturbances may actually serve to maximize ecosystem diversity.

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​Moderate Disturbances

Low level disturbances -- species tend to overspecialize

• Ex: If a river is always stable, then most competitive species are those best adapted to the river's level.

Competition between species, NOT adaptation to change, will determine makeup of ecosystem.

Dominant species will outcompete all others for food & resources.

Less competitive populations decrease, less biodiversity.

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​Light Disturbances

Species are at risk of total extinction.

• Ex: No species can adapt to survive a direct meteor hit

Only highly mobile individuals can escape.

High-stress environments can be lethal to entire ecosystems.

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​High Disturbances

• Primary usually takes longer than secondary

  It can take a year for pioneer species or annual plants to come in

• 3-4 years for shrubs and bushes to come in

• 5-150 years for small trees

• and 150 or more years for large trees and for the community to be in equilibrium which is a climax community

• Growth and development of an ecosystem

• Allows ecosystems to thrive once again and balance to return

• Generates biodiversity over time

• Soil stabilization

• Nutrient enrichment - humus formation

• Promote nitrogen fixation and carbon cycle

• Reduction of light availability

• Reduction of wind exposure

• Temperature moderation

• Lichens are commonly recognized as a symbiotic association of a fungus and a chlorophyll containing partner, either green algae or cyanobacteria, or both.

• The fungus provides a suitable habitat for the partner.

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​Lichen - Mutualism

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