D4.2.12 Ecological succession and its causes (HL) Notes

Ecological Succession Gradually Transforms Ecosystems

Species and Abiotic Factors Interact to Shape Ecosystems

1. Species Modify the Environment: Pioneer species influence abiotic factors such as soil formation and nutrient levels.
2. Abiotic Factors Shape Species Composition: Changes in light availability, temperature, and soil conditions favor different species as succession progresses.

Primary Succession Begins on Bare Surfaces

Primary succession occurs where no soil exists, such as after volcanic eruptions or glacier retreats.

Example

Lichens and mosses colonize bare rock, breaking it down to create soil for grasses and shrubs.

Secondary Succession Follows Disturbances in Established Ecosystems

Secondary succession takes place in areas where soil is present, but vegetation has been removed, like after a forest fire.

Abiotic Events and Biotic Factors Trigger Succession

1. Abiotic Events: Natural disasters such as avalanches or floods remove existing vegetation, creating conditions for new growth.
2. Biotic Factors: Organisms like beavers or grazing animals initiate changes in ecosystems by altering landscapes or food availability.

Grasslands Transform Through Succession

1. Consider an area of grassland colonized by shrubs and trees:
   1. Abiotic Changes: Trees increase nutrient concentration, water retention, and humidity while reducing light at ground level.
   2. Species Turnover: Grass species adapted to open sunlight are replaced by those suited to forest conditions.
   3. Animal Changes: The animal community shifts as plant species change, highlighting interdependence between plants and animals.

Climax Communities Represent Stability

1. A climax community is a stable ecosystem where species composition and abiotic conditions remain consistent unless significantly disturbed.