Transcript Plant Ecology - Chapter 12 Disturbance & Succession

Plant Ecology - Chapter 12
Disturbance & Succession
Succession
Temporal patterns in communities
Replacement of species by others
within particular habitat (colonization
and extinction)
Non-seasonal, continuous, directional
Degradative succession
Decomposers breaking down organic
matter
Leads to disappearance of everything,
species included
Autotropic succession
Does not lead to degradation
Habitat continually occupied by living
organisms
Two types of autotropic
succession
Allogenic succession
Autogenic succession
Allogenic succession
Serial replacement of species driven by
changing external geophysical
processes
Examples:
1) silt deposition changing aquatic habitat
to terrestrial habitat
2) increasing salinity of Great Salt Lake
Autogenic succession
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
In an area that
previously did not
support any
community
Primary succession
Example: terrestrial
habitat devoid of soil
In an area that previously
supported a community,
but now does not
Secondary succession
Example: terrestrial
habitat where vegetation
was destroyed, but soil
remained
Disturbances
Relatively discreet
event in time that
causes abrupt change
in ecosystem,
community, or
population structure
Changes resource
availability, substrate
availability, or the
physical environment
Disturbances
Intensity, size,
frequency
Small disturbances of
low intensity are much
more frequent than
large disturbances of
high intensity
Disturbances
Gaps
Fire
Wind
Water
Animals
Earthquakes, volcanoes
Disease
Humans
Primary succession
Volcanic eruptions
Glaciers
Secondary
succession
Floods
Fires
Rate of succession
Primary - slow - may take 1000s of
years
Secondary - faster - fraction of the time
to reach same stage
Autogenic succession
begins…
First community comprised of
rselected species - pioneer species
r-selected species
Good colonizers
Tolerant of harsh conditions
Reproduce quickly in unpredictable
environs
Example: lichens
r-selected species
Primary - colonized by seeds, spores,
via wind, water
Secondary - wind-dispersed seeds,
seed banks
Pioneer species
Carry out life processes and begin to
modify habitat
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
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
Communities may gradually become
dominated by K-selected species
Good competitors, able to coexist with
others for long periods of time
Stability
Communities may become stabilized on
some scale
Reach equilibrium (dynamic)
Little or no change in species
composition, abundance over long
periods of time
Climax community
End stage of succession
Will climax stage be reached?
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
Relay Floristics
Relay Floristics
Predictability of Succession
Deterministic- process with a fixed outcome
Community restoration
via succession?