AHL Content Statements

• D4.2.12

  Ecological succession and its causes
  

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  Succession can be triggered by changes in both an abiotic environment and in biotic factors.
  

• D4.2.13

  Changes occurring during primary succession
  

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  Use any suitable terrestrial example to illustrate these general principles: increases in size of plants, amount of primary production, species diversity, complexity of food webs and amount of nutrient cycling.
  

• D4.2.14

  Cyclical succession in ecosystems
  

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  Students should appreciate that in some ecosystems there is a cycle of communities rather than a single unchanging climax community. Students should refer to an example.
  

• D4.2.15

  Climax communities and arrested succession
  

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  Given any specific environmental conditions, ecological succession tends to lead to a particular type of climax community, but human influences can prevent this from developing. Use grazing by farm livestock and drainage of wetlands as examples.