Succession

• Succession is a way in which ecosystems are changing over time --> occurs as a result of changes to the environment causes plant and animal species present to change
• Two types
  • primary succession --> area of land is newly formed or exposed so there is no soil or organic matter to begin with
    • when volcanoes erupt, depositing lava
    •  sand is blown by the wind or deposited in the sea to make new sand dunes
    • mud is deposited in river estuaries 
    • glaciers retreat depositing rubble and exposing rock
  • secondary succession --> areas of land where soil is present but contains no plant or animal species

Stages of succession

• Steps = seral stages
• At each seral stage key species can be identified than change the abiotic factors, especially the soil, to make it more suitable for the next species
  1. barren land
  2. pioneer community with colonisers
  3. intermediate community with secondary colonisers, tertiary colonisers and scrubland
  4. climax community with dominant species (which arises from secondary succession or primary succession)
• Pioneer community
  • begins by the colonisation of inhospitable environment by a pioneer species 
  • they often arrive as spores or seeds that have been carried on the wind from other land masses
  • pionner species need a number of adaptations to colonise the environment:
    • ability to produce large quantities of seeds and spores that can be carried on the wind
    • seeds that germinate rapidly
    • ability to photosynthesise
    • tolerance to extreme conditions
    • ability to fix nitrogen from the atmosphere
• Intermediate community
  • over time, weathering of the bare rock produces particles that when mixed with the dead matter of the pioneer species forms soil
  • the organic component of soil is humus
  • the soil becomes able to support the growth of a new species of plant aka secondary colonisers --> arrive as spores or seeds
  • as the conditions improve further new plant species arrive as ferns aka tertiary colonisers --> have waxy cuticle to protect them from water loss
  • at each stage the rock continues to be eroded so the soil gets better until it can support flowering plants such as grasses, then shrubs, then small trees
  • SO it has multiple seral stages and at each seral stage the plant and animal species are better adapted to the current conditions of the ecosystem --> they outcompete the species previously present and become the dominant species
• Climax community
  • final seral stage
  • community is in stable state
  • there are normally a few dominant plant and animal species --> which ones depends on the climate
  • although biodiversity increases as succession takes place, the climax community isn't also the most biodiverse
  • biodiversity tends to reach its peak mid-succession and then decreases as the dominant species outcompete the pioneer communities
• Animal succession
  • primary consumers (insects) are the first to colonise as they consumer and shelter in the mosses and lichens
  • secondary consumers arrive when a suitable food source has been established and the existing plant cover will provide them with suitable habitats
  • eventually larger organisms like mammals and reptiles colonise the area when the biotic conditions are favourable
• Deflected succession
  • human activities can halt natual succession
  • when succession is stopped artificially its called plagioclimax
  • agriculture is the main reason delfected succession occurs 
    • grazing and trampling of vegetation by animals
    • removing existing vegetation to plant crops
    • burning as a means of forest clearance