Ecological Succession
Environment
Ecological succession is the natural, gradual process through which one biological community replaces another over time. Plants, animals, microorganisms and physical factors (soil, water, climate) work together and continuously modify an area, leading to predictable changes in species composition.
TYPES OF SUCCESSION
1. Primary Succession
Occurs on completely bare areas with no soil—new rocks, lava fields, sand dunes, new islands, glacial deposits.
Pioneer species like lichens and mosses colonise first, bring soil formation, followed by grasses, shrubs, and trees.
Ends with the development of a stable climax community.
Seral Stages (Seres):
• Hydrosere – succession in water
• Xerosere – succession in dry regions
• Lithosere – on rocks
• Psammosere – on sandy areas
• Halosere – in saline conditions
• Senile – on dead organic matter
• Ecosere – large-scale vegetation development
2. Secondary Succession
Occurs where a previous community existed but was disturbed by fire, flood, storm, agriculture or deforestation.
Since soil, seeds and microorganisms remain, succession is much faster than primary succession.
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TYPES BASED ON DRIVING FORCES
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AUTOGENIC SUCCESSION
Organisms themselves bring changes—plants alter soil, trees create shade, litter accumulates. These internal changes push succession forward.
ALLOGENIC SUCCESSION
External forces drive change—soil erosion, deposition, floods, animals as dispersers, pollinators or grazers.
AUTOTROPHIC SUCCESSION
Begins in an inorganic environment, dominated by autotrophs (plants, algae). Includes both primary and secondary succession.
HETEROTROPHIC SUCCESSION
Begins in an organic-rich environment—rotting logs, dung, sewage. Dominated initially by bacteria, fungi, insects. Energy declines as organic matter is consumed.
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MECHANISM OF SUCCESSION
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1. Nudation – Creation of a bare area (landslide, fire, drought, volcanic activity, human disturbance).
2. Invasion – Arrival and establishment of species.
• Migration – seeds/spores reach the site
• Ecesis – establishment and adjustment
• Aggregation – increase in population
3. Competition – Species compete for nutrients, space, light and water.
4. Reaction – Organisms modify environment, making it suitable for some species and unsuitable for others.
5. Stabilisation/Climax – A stable, final community forms and persists until a major disturbance occurs.
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CAUSES OF SUCCESSION
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• Rainfall and climate changes
• Temperature variations
• Humidity differences
• Soil development
• Migration and competition among species
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CHARACTERISTICS OF SUCCESSION
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• Predictable and systematic
• Leads to changes in species composition
• Increases biodiversity
• Improves nutrient cycling
• Leads toward a stable climax community
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Subject: Environment
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