SUCCESSION

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SUCCESSION
Changes in the species composition of a community
over time in response to disturbance
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Two views of succession
Clements the community as superorganismorderly,
predictable succession from pioneer species to
climax community
Gleason the community as a collection of
individual species, with individual physiological
requirements
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Idealized, old-field, Clementsian succession
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Primary succession
Colonization of newly exposed substrate
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Glacier Bay glacier in retreat
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Secondary succession
colonization after disturbance
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DISTURBANCE
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Cryptantha a fire-follower
An early successional species
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Manzanita some re-sprout, some re-seed
--all are chaparral climax species
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Good colonizers Good competitors
 
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Q1 the shift is on . . . toward early
successional or climax communities? Consequences
?
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Q2 Whats wrong with a world full of
dandelions, starlings, fox squirrels, and us?
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Mechanisms of succession two hypotheses

• Facilitation early colonizers facilitate the
  species that follow
• Inhibition early species tend to exclude others,
  which get established only when early ones die off

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Phyllospadix late successional grass in kelp
beds and tide pools
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Ecosystem stability and recovery

• Stability Absence of change.
• Resistance Ability to maintain structure and
  function in spite of potential disturbance.
• Resilience Ability to recover readily from
  disturbance.

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Q Which is more stable, a diverse or a
simple ecosystem? More resistant? More resilient?
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Disturbance (drought) and species diversity
Mulder et al., 2001
Number of species planted
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