Community Development and SpeciesArea Relationships

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Community Development and Species-Area
Relationships

• BIOL 500
• 9 November 2009

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Community DevelopmentEcologicalSuccession
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Primary vs. Secondary Succession

• Primary succession occurs on bare soil
• Ex Mt. Saint Helens
• Secondary succession follows disturbance in areas
  having some vegetation already
• Ex Old-field succession

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Figs. 18.1018.12 pp. 366-67
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Clements View of Succession

• Community-as-Superorganism Concept
• aka Relay Floristics Model
• Seres ( successional stages) analogous to
  developmental stages of an organism
• Monoclimax single, predictable climax community
  (the community that remains stable, ending
  succession)

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Fig. 18.5 p. 358
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Egler's Initial Floristic Composition Model

• Much more individualistic
• Contingency what plant species happen to
  colonize first will greatly influence both the
  sequence and the climax
• Inhibition of earlier stages by later stages

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Connell and Slatyer's Facilitation, Inhibition,
and Tolerance Model

• Facilitation drives Clements relay floristics
  model
• A modifies environment favorably for B, etc.
• Inhibition drives Eglers initial floristic
  composition model
• B suppresses growth of A, etc.
• Tolerance refers to the ability of a species at
  any one stage to tolerate
• resource levels (important early in sequence)
• level of competition for soil nutrients and
  light (important later in sequence)

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Succession and Plant Life Histories

• Whether a species predominates in early vs. late
  succession tends to correlate with features of
  its ecology and life history
• Ability to colonize
• Ability to tolerate competition with other
  species

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Table 18.1 p. 359
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Fig. 18.7 p. 364
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The Climax Community

• Climax vegetation is stable and self-perpetuating
• Clementsmonoclimax
• Tansleyadvocated polyclimax idea
• Historical contingency determines climax
  composition
• Whittakerdeveloped idea of pattern climaxa
  continuum of climax-condition possibilities based
  on entire suite of physical factors

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Other Concepts of Ecological Succession

• Communities that do not climax
• Ex Prairies, which remain stuck in
• early sere because of frequency of
• disturbance by fire
• Transient successionno climax possible due to
  gradually diminishing resources
• Exs Dung piles
• Carcasses

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Fig. 18.14 p. 368
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Fig. 18.15 p. 369
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Species-Area RelationshipsIsland Biogeography
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Arrhenius equation (1921)

• S cAz
• S species richness
• A island area
• z slope
• c constant
• Linear form logS logc z?logA

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Explaining the ArrheniusSpecies-Area Relationship

• Increased area increased habitat heterogeneity
  (more niches to fill)
• Increased area increased population sizes of
  resident species
• Less chance of their stochastic local extinction
• Increased area larger target for dispersing
  would-be colonizing species

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Figs. 21.19 21.20 p. 442

• c depends on units of area that are used, but z
  does not
• Typically, z ranges between 0.20 and 0.35

z 0.30
z 0.32
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The Theory of Island Biogeography

• 1967 book by Robert A. MacArthur (Princeton) and
  Edward O. Wilson (Harvard)
• Colonization curve declines with rising S, as
  fewer species are available to colonize
• Local extinction curve rises with rising S, as
  interspecific interactions intensify

Fig. 21.21 p. 442
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The Dynamic Equilibrium

• Point at which the two lines cross
• Balance of new colonists arriving and resident
  species going locally extinct
• Gains Losses

Fig. 21.22 p. 443
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Krakatau

• Indonesian island wiped clean of all life by
  enormous volcanic eruption in 1883
• 1883 0 bird spp.
• 1908 13 bird spp.
• 1921 2 bird spp. lost, 16 gained (27 total)
• 1935 5 bird spp. lost, 5 gained (27 total)

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MacArthur and WilsonsArea Effect

• Larger areas house larger resident populations
  less prone to stochastic extinction

Fig. 21.22 p. 443
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MacArthur and WilsonsDistance Effect

• More isolated habitat islands are more difficult
  to reach

Fig. 21.22 p. 443
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Area and Distance Effects Combined

• Small, isolated islands
• Rare colonists
• High local extinction rate
• Low Sequilibrium
• Large, nearby islands
• Frequent colonists
• Low local extinction rate
• High Sequilibrium

Fig. 21.22 p. 443
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HANDOUTSimberloff and Wilson 1969
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NonequilibriumIsland Biogeography

• Dynamic equilibria are possible only when
  colonization can occur
• Stranded populations may show ecosystem decay,
  with an area effect on S but no distance effect
  on S
• Islands slowly bleed species richness
• More rapid loss for smaller islands
• Occurs naturally, but esp. important in
  anthropogenically-isolated habitats

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HANDOUTBrown 1971
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HANDOUTDiamond 1984
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HANDOUTNewmark 1987