Page 36 of the CGP A2-Level Biology revision guide.

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  • Succession
    • Succession is the process by which an ecosystem changes over time.
      • The Biotic conditions change as the Abiotic conditions change.
      • Ecosystem= All the organisms living in a particular are and all the non-living conditions.
    • There are two types of succession.
      • Primary Succession
        • This happens on land that's been newly formed or exposed.
        • The abiotic conditions are hostile. Only pioneer species can grow because they're specialized to cope with the harsh conditions.
          • The pioneer species change the abiotic conditions- they die and microorganisms decompose the Humus. This forms basic soil.
            • Humus= Dead organic matter.
            • This makes the conditions less hostile, which means new organisms can move in and grow.
              • These then die and are decomposed, adding more organic material, making the soil deeper and richer in minerals .
                • Larger plants like shrubs can start to grow in the deeper soil, which retains even more water.
      • Secondary Succession
        • This happens on land that's been cleared of all the plants, but where the soil remains.
    • Succession occurs in seral stages.
      • At each stage, different plants and animals that are better adapted for the improved conditions move in an out compete the  original plants and animals.
        • They become the Dominant species in the ecosystem.


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