Succession

• Succession

  = The progressive replacement of one dominant type of species or community by another in an ecosystem, until a stable climax community is established.

  • Occurs as a result of changes to the environment (abiotic) causing plant and animal species present to change.
• Primary succession

  = Occurs on an area of land that has been newly formed or exposed such as bare rock. There is no soil or organic material present to begin with.
• Secondary succession

  = Occurs on areas of land where soil is present, but it contains no plant or animal species. Eg: bare earth that remains after a forest fire.
• Primary succession occurs when

  • Volcanoes erupt, depositing lava- when lava cools and solidifies igneous rock is created.
  • Sand is blown by the wind or deposited by the sea to create new sand dunes.
  • Silt and mud are deposited at river estuaries.
  • Glaciers retreat depositing rubble and exposing rock.
• Stages of succession

  Succession take place in a number of stages= seral stage

  • At each seral stage key species an be identified that change the abiotic factors to make it more suitable for the subsequent existence of other species.
• Stages of succession

  Succession take place in a number of stages= seral stage

  • At each seral stage key species an be identified that change the abiotic factors to make it more suitable for the subsequent existence of other species.
• Pioneer community

  Primary succession begins by the colonisation of an inhospitable environment, by organisms known as pioneer species, this represents the first seral stage.

  • These species arrived as spores or seed carried by the wind.
  • Eg: algae and lichen
• Adaptations that enable them to colonise bare environments

  • Ability to produce large quantities of seeds or spores, which are blown by the wind and deposited on the new land.
  • Seeds that germinate rapidly
  • Ability to photosynthesise to produce their own energy
  • Tolerance to extreme environments
  • Ability to fix nitrogen from the atmosphere, so adding to the mineral content of the soil.
• Intermediate community

  • Overtime weathering of bare rock produces particles that form the basis of a soil that cant support other species on its own.
  • When organisms of pioneer species die and decompose, small organic products are released into the soil= humus
  • The soil becomes able to support the growth of new species of plant= secondary colonisers as it contains minerals and can retain water.
  • Secondary colonisers arrived as seeds or spores.
• • Environmental conditions improve so new species of plant arrived= tertiary colonisers. These plants have a waxy cuticle that protects them from water loss so can survive in conditions without an abundance of water.
  • At each stage the rock continues to be eroded and the mass of organic matter increases. When organisms decompose they contribute to a deeper more nutrients rich soil which retains more water so abiotic conditions are more favourable.
  • This period is known as the intermediate community as multiple seral stages evolve until climax conditions are attained.
• Intermediate community

  At each seral stage different species are better adapted to current conditions in ecosystem, they outcompete previous species to become the dominant species.
• Climax community

  The final seral stage is the climax community.

  • The community is in a stable state and will show very little change over time.
  • There are few dominant species
  • Which species make up the climax community depends on the climate
  • Often not very biodiverse
  • Biodiversity tends to decrease due to the dominant species outcompeting other species.
• Deflected succession

  Human activities can prevent the ecosystem from reaching climax community.

  • Plagioclimax= when succession is stopped artificially
  • Agriculture is the main reason for deflected succession: grazing and trampling of vegetation results in large areas remaining as grassland, removing existing vegetation to plant crop means the crop becomes the final community, burning for deforestation leads to an increases in biodiversity