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					Ecological Succession
What is ecological succession?
• Ecological succession is the gradual and
  predictable process by which ecosystems
  change and develop over time.
• Nothing remains the same and habitats
  are constantly changing.
         Primary Succession
• Occurs after the creation of a new habitat

• e.g. lava flow, glacier retreat, sand dune
  formation, artificial ponds, artificial reefs

• Areas which have never had organisms
  growing on them

• Conditions are unfavorable for life at first
Primary Ecological Succession
 Occurs on surfaces
 where no soil exists.
 After a Lava flow or
 retreating glacier
           Primary
           species
Primary Succession
         Secondary Succession
• Community development in areas that were previously
  occupied by a community

• Occurs after a disturbance

• e.g. loss of trees by disease, wind or fire; logs clearing
  areas in intertidal zone; overturning of boulders in
  intertidal zone

• Conditions are therefore favorable since seeds, spores
  and even resistant animals or plants may remain and
  there is often a well developed soil

• More rapid than primary succession
Secondary Ecological Succession
                      Occurs when
                      a climax
                      community
                      is disturbed.
                      Soil already
                      exists.

                      Ex. Land after a
                      forest fire, land
                      cleared for
                      farming is
                      abandoned
Secondary Succession
    How does Succession Occur?
•    Through a series of stages:

    – Pioneer species arrive

    – Early colonizers with good dispersal
      mechanisms (r-selected species); fast
      growth rate; high photosynthetic rate;
      minimal environmental demands

    – Opportunistic organisms settle

    – e.g. diatoms, sea lettuce, scotch broom
  How does succession occur?
Seral stages

• waves of temporary organisms displace
  pioneer species through competition

Climax community
• End point of succession
• Climax community – VA is a deciduous
  oak-hickory (hardwood) forest.
         Climax Community

• Most permanent of all the stages
• Stage at which system has reached
  steady-state equilibrium
• May take 100’s or 1000’s of years to reach
  this stage.
• During succession species modify the physical
  environment making it more suitable for new
  species and less suitable for those already there


• Pioneer species are often poor competitors and
  are replaced by stronger competitors that have
  greater environmental demands


• Later communities are often more complex than
  earlier communities

				
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posted:9/26/2012
language:English
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