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Lecture 18: Community change. EEES 3050. Succession. Succession: Definition: The process of directional change in vegetation during ecological time. Primary Succession: Succession on new areas Secondary Succession: The recovery of disturbed new sites. . Example: Dune succession.

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  • Succession:
    • Definition:
      • The process of directional change in vegetation during ecological time.
    • Primary Succession:
      • Succession on new areas
    • Secondary Succession:
      • The recovery of disturbed new sites.
example dune succession
Example: Dune succession
  • Henry Cowles (1899)
    • Studied sand dune vegetation on the shores of Lake Michigan.
    • Brief history of Lake Michigan Lake levels.
example dune succession1
Example: Dune succession
  • “ideal” system for studying succession.
    • Why?
      • Same initial substrate.
      • Same relief
      • Same available flora and fauna.
    • Thus, only differences between dunes should be time, biological processes of succession, and random events.
example dune succession2
Example: Dune succession
  • Primary Assumption
    • Exchanging space for time.
stages of dune succession
Stages of dune succession
  • Bare soil
    • Bare sand produced by drop of lake and blowouts
    • Wind continually shifts sands.
stages of dune succession1
Stages of dune succession
  • 1) Bare soil
    • Bare sand produced by drop of lake and blowouts
    • Wind continually shifts sands.
  • 2) Colonization
    • Establishment of grasses (marram grass).
      • Usually by rhizomes
      • “Likes” moving sands
        • Not found in areas after about 20 years.
stages of dune succession2
Stages of dune succession
  • 3) Colonization of additional grasses.
    • Help stabilize dunes.
stages of dune succession3
Stages of dune succession
  • Colonization of additional grasses.
    • Help stabilize dunes.
  • 4) Colonization by woody species
    • 1st usually cottonwoods
    • Also willow and sand cherry.
  • Dune becomes stabilized
stages of dune succession4
Stages of dune succession
  • 5) After stabilization
    • Jack pine & white pine
  • 100 to 150 years later
    • Black oak trees.
What other systems can be used by exchanging time with space?
    • Retreating glaciers.
  • Examples of succession
    • Old farm field
    • Post-burn
    • Tree gaps
    • Volcanic lava flows
    • Disease
    • Human disturbance
succession an historical perspective
Succession: an historical perspective.
  • 4 major hypotheses:
  • Relay floristics/monoclimax hypothesis
  • Initial floristic composition
  • Tolerance Model
  • Random colonization
succession an historical perspective1
Succession: an historical perspective.
  • Clements view: Monoclimax Hypothesis
    • Called relay floristics by Egler
Clements view: Monoclimax Hypothesis
    • Key assumption:
      • Species replace each other through each stage because they change the environment such that it is more suitable for the next species.
    • Climax community in any region is determined by climate.
nature and structure of the climax by frederic clements 1936
Nature and Structure of the Climax by Frederic Clements (1936)
  • Has a category for everything!
    • Climax state
    • Proclimax
    • Disclimax
    • Subclimax
  • Climax community definition:
    • Final or stable community in a successional series. It is self-perpetuating and in equilibrium with the physical and biotic environments.
  • Initial floristic composition
    • Proposed by Elger (1954)
  • Succession is heterogeneous.
  • Development depends on who gets there first.
  • Initial floristic composition
    • Still species have no competitive advantage.
    • Dominant community merely a matter of who gets there first and lives the longest.
    • Succession proceeds from short-lived to long-lived species.
  • Tolerance model.
    • Could lead to Tilman’s resource ratio hypothesis.
    • Species are replaced by other species that are more tolerant of limiting resources.
Random Colonization
    • Succession involves only the chance survival of different species and the random colonization by new species.
  • Thoughts?
    • Not a realistic scenario, but established a null model to test against.
    • If not random, than some process must be at work.
what model fits the dune scenario
What model fits the dune scenario?
  • Monoclimax?
  • Initial floristic composition?
  • Tolerance?
  • Random Colonization?
  • We only examined the dominate species!
    • Perhaps a mix of climax and random colonization.
types of species
Types of species
  • pioneers (r-species)
    • short-lived
    • high reproduction
    • poor competitors
    • emphasize dispersal
  • climax species (K-species)
    • long-lived
    • low reproduction
    • strong competitors
    • emphasize survival
type of succession
Type of Succession
  • primary:
    • new site, never before home to a community
    • Examples: ash flow, new sediments, retreat of glacier
  • secondary:
    • disturbed site
      • most common
    • Examples: abandoned farm field, flood, forest fire, disease/insect outbreak.
    • regenerative:
      • replacement with same species
      • Examples: Periodic disturbance
community change
Community Change
  • Patch Dynamics
    • Small-scale changes in a community
    • Examples
      • Degeneration of plants
      • Tree fall gap
      • Dispersal of organisms
      • Wave action
      • Burrowing animals