Covers the entire section on ecological succession. Includes notes from the textbook, as well as additional class, video and research information, diagrams and practice questions.
Applicable to all IEB Grade 12s.
Written by a 90% < candidate.
Ecological succession
= A natural and predictable pattern of gradual change over time in the types of species in a
community following a disturbance.
e.g. Knysna Fires = ecologists new what would happen in each environment.
Our indigenous forests barely burnt as they are so wet, have a canopy, keep moisture in.
Open fynbos and alien species = burnt easily and the alien vegetation spread seeds.
Type 1: Primary succession
Begins on sites that have not previously had plants growing on them (no soil before)
Examples: beaches, larva flows, severe landslips and bare rock.
Type 2: Secondary succession
Begins in areas where there is a disturbance that removes some or all of the species, but the
soil remans.
Community structure
Is not static, but it determined over time by succession that takes place as a result of:
- Disturbances
. a. Caused by physical disasters, such as storms, floods, fires.
. b. Caused by humans or animals, such as abandoned crop fields, overgrazing, logged area.
. c. Caused by climate change.
- Competitive interactions
Stages in succession
Order of change is not random.
Communities initially have a small number of simple species which are gradually replaces by a
large number of complex species.
Stage 1: Pioneer species
= first species to colonise an area
Bare ground favours pioneer plant species.
These species grow best where there is little competition.
Features:
- Are able to withstand extreme variations in climate
- Establish rapidly as they have shallow roots
- Have spores or seeds and are light
- Do not grow in the shade
Pioneer species prepare the surroundings for later colonists by altering the biotic and abiotic
environment.
They do this by:
- Building up, stabilising and enriching the soil
- Altering the amount of light available by providing shade
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