Ecological Succession
Succession


Succession is a series of regular, predictable changes in
community structure over time.
Activities of organisms change their surroundings and make
the environment suitable for other kinds of organisms.
– Examples of activities:




Climate
Available seed sources
Frequency of disturbance
Invasions of organisms
Succession
 There
are 2 kinds of ecological
succession
– Primary succession
– Secondary succession
 The
difference between the two is
the starting point.
Primary Succession


Primary
succession
begins with a
total lack of
organisms and
bare mineral
surfaces (for
example a lava
field) or water.
There is no
gross
productivity.
Secondary Succession
 Secondary
succession occurs when an
existing community is disturbed or
destroyed (for example by fire, flood,
or human activity) but much of the soil
and some of the organisms remain.
Secondary Succession
 Gross
productivity is low due to
initial conditions and low density of
producers.
 Few organisms = little respiration =
low energy lost = high net
productivity.
– The system is growing and biomass is
accumulating.
Secondary Succession
– Because the soil and nutrients remain,
the process can advance more rapidly
than primary succession.
– Plants and organisms that survive the
disturbance can grow quickly and
reestablish themselves.
– Nearby undamaged communities can
serve as sources of seeds and animals.
– The new climax community is likely to
resemble the destroyed community.
Succession
 There
are 2 places where ecological
succession takes place.
– Terrestrial
– Aquatic
Terrestrial Primary Succession

Terrestrial primary
succession
– A pioneer community
is a collection of
organisms able to
colonize bare rock (e.g.,
lichens).


Lichens help break
down rock and
accumulate debris,
helping to form a thin
soil layer.
The soil layer begins to
support small forms of
life.
Terrestrial Primary Succession
 Steps
to terrestrial primary succession
1.Lichen community replaced by annual
plants.
2.Annuals replaced by perennial
community.
3.Perennial community replaced by shrubs.
4.Shrubs replaced by shade-intolerant trees.
5.Shade-intolerant trees replaced by shadetolerant trees.
6.Stable, complex, climax community
eventually reached.
Terrestrial Primary Succession
Terrestrial Secondary Succession

An example of
terrestrial
secondary
succession in
the Pacific
Northwest is
clear cutting.
Secondary Terrestrial
Succession
Each step in the process is known as a
seral stage, and the sequence of stages is
called a sere.
Secondary succession on land
Climax Community

A climax community
is a relatively stable,
long-lasting
community that is the
result of succession.
The kind of climax
community that
develops is primarily
determined by climate
and soil type.
– Eg. Pacific Northwest
old growth forest or a
desert
Climax Communities
 Climax
communities show certain
characteristics when compared with
successional communities.
– Climax communities maintain species
diversity for an extended period.
– They contain multiple specialized ecological
niches.
– They maintain high levels of organism
interactions.
– Climax communities recycle nutrients while
maintaining a relatively constant biomass.
Climax Community
 The
general trend in succession is
toward increasing complexity and
more efficient use of matter and
energy.
A coral reef
Climax Community
 Increased
consumer community
means a high gross productivity
which is balanced by respiration (loss
of energy) so net productivity
approaches 0
– The production:respiration (P:R)
approaches 1.
Climax Community
 If
disturbed by continual human
activity or natural disasters,
ecological communities are not
allowed to reach climax
communities.
– The community remains at an
equilibrium at a sub-climax community
 Eg.
Logging every 75 years.
Diversity and Resiliency
 The
more diverse the habitat, the
more genetic and species diversity,
– the more diversity = more resilient to
change.
– The more resiliency = faster
recuperation due to a disturbance.
Aquatic Primary Succession
 Aquatic
primary succession
– Except for oceans, most aquatic
systems are considered temporary.
– All aquatic systems receive inputs of soil
particles and organic matter from
surrounding land.
– This results in the gradual filling of
shallow bodies of water.
 Roots
and stems below water accumulate
more material.
 Establishment of wet soil.
Primary Succession
Primary succession from a pond to a wet meadow.
Floating Bog
 This
graph shows how GPP and
respiration differ as ecological
succession progress.
Changes During Succession
Size of organisms increases—more trees
 Energy flow is more complex—more
complex food webs
 Soil depth, humus, water-holding
capacity, mineral content and nutrient
cycling all increase
 Biodiversity increases because more
niches (lifestyle opportunities) appear,
and then falls as the climax community is
reached

Equilibria

A steady-state
equilibrium is when the
recently observed behavior
of the system will continue
into the future. It refers to
a system that is not closed
and there is a constant
input of reactants and
outflow of products.
– should be understood as
the common property of
most open systems in
nature.
– Example: A plant
Equilibria

A static equilibrium is when the system
experiences no change.
– It is a condition to which natural systems can
be compared.
– There are no naturally occurring static
equilibrium scenarios in ecosystems.
Disturbances

The relative
stability of an
equilibrium is the
tendency of the
system to return to
that original
equilibrium
following
disturbance rather
than adopting a
new one.
– Example:
ecological
succession.