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Community Ecology
Chapter 9
Succession
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Temporal patterns in communities
Replacement of species by others within
particular habitat (colonization and
extinction)
Non-seasonal, continuous, directional
Degradative succession
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Decomposers breaking down organic
matter
Leads to disappearance of everything,
species included
Autotropic succession
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Does not lead to degradation
Habitat continually occupied by living
organisms
Two types of autotropic
succession
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Allogenic succession
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Autogenic succession
Allogenic succession
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Serial replacement of species driven by
changing external geophysical processes
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Examples:
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1) silt deposition changing aquatic habitat to
terrestrial habitat
2) increasing salinity of Great Salt Lake
Autogenic succession
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Change of species driven by biological
processes changing conditions and/or
resources
Example: organisms living, then dying, on
bare rock
Autogenic succession can occur
under 2 different conditions
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In an area that
previously did not
support any community
Primary succession
Example: terrestrial
habitat devoid of soil
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In an area that
previously supported a
community, but now
does not
Secondary succession
Example: terrestrial
habitat where
vegetation was
destroyed, but soil
remained
Primary succession
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Volcanic eruptions
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Glaciers
Secondary
succession
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Floods
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Fires
Rate of succession
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Primary - slow - may take 1000s of years
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Secondary - faster - fraction of the time to
reach same stage
Autogenic succession begins…
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First community comprised of r-selected
species - pioneer species
r-selected species
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Good colonizers
Tolerant of harsh conditions
Reproduce quickly in unpredictable
environs
Example: lichens
Pioneer species
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Carry out life processes and begin to
modify habitat
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Extract resources from bare rock
Break up/fragment rock with roots
Collect wind-blown dust, particles
Waste products accumulate
Die and decompose
Soil development begins
Continuing change
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Colonizers joined by other species suited
for modified habitat
Eventually replace colonizers
Better competitors in modified habitat
Less r-selected, more K-selected
More change
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Communities gradually become dominated
by K-selected species
Good competitors, able to coexist with
others for long periods of time
Stability
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Communities become stabilized
Reach equilibrium
Little or no change in species composition,
abundance over long periods of time
Climax community
End stage of succession
Will climax stage be reached?
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Rarely is climax stage reached quickly
Slow succession most common, climax
stage almost never achieved
Community usually affected by some
major disturbance (e.g., fire) before climax
stage is reached
Resets succession, forces it to start again
from some earlier stage
Terrestrial succession
Lake or pond succession