Transcript Ecological Succession

4.1.5 Changes in Ecosystems:
Ecological Succession
of a Forest Biome
Assessment Statements
• 4.1.5 Explain the relationships among ecosystem
stability, diversity, succession and habitat.
• 2.6.5 Describe the concept and processes of succession
in a named habitat.
• 2.6.6 Explain the changes in energy flow, gross and net
productivity, diversity and mineral cycling in different
stages of succession.
• 2.6.7 Describe factors affecting the nature of climax
communities.
Questions to think about:
– How does diversity change through succession?
– How are habitat diversity and genetic diversity
related?
– What provides stability in an ecosystem?
– How does human activity modify succession?
– What factors determine if an ecosystem can survive
change?
https://www.youtube.com/watch?v=jZKIHe2LDP8
There are two main types of
Ecological Succession
• Primary Succession: The process of
creating life in an area where no life
previously existed.
• Secondary Succession: The process of
re-stabilization that follows a disturbance
in an area where life has formed an
ecosystem.
Succession Defined:
• Natural, gradual changes in the types of
species that live in an area;
• The gradual replacement of one plant
community by another through natural
processes over time
Primary Succession
• The development of an
ecosystem in an area that
has never had a
community living within it
• Primary succession
generally occurs after a
natural disaster which
lead to a major loss in
diversity:
–
–
–
–
Volcanic eruption
Tsunami
Meteor impact
Glacial flow
Primary Succession
• Begins in a place without any soil
– In the beginning there is only rock, sand,
volcanic ash.
– Since there is no soil, there is no community.
Why is there no soil?
In order for there to be soil there
must be nutrients like nitrogen.
So … why is there no soil?
Primary Succession
. • Lichens, algae & bacteria
begin growing on the
rocks.
• Harsh conditions but
limited competition.
• Over many years lichens
break down rock into
sand.
• Weathering and erosion
break down rock into
sand.
Primary Succession
• Lichens that do not need soil to survive
• Called PIONEER SPECIES (Why?)
Primary Succession
• Lichens grow larger.
• Some die.
• Decomposers arrive and break down the
lichens. The dead lichens and waste
materials of the decomposers enrich the
sand.
• Nitrogen cycle begins. Eventually enough
nutrients enter the sand and it becomes soil.
Primary Succession
• Seeds/spores are blown in by the wind or
carried in by animals. Simple plants like
mosses and ferns can grow in the new soil
• The plants grow and the soil gets enriched as
plants die..
Primary Succession
• Herbs and weeds can grow in the thicker,
enriched soil
• Roots start holding soil in place
Primary Succession
• The simple plants die, adding more
organic material
• The soil layer thickens, and grasses,
wildflowers, and other plants begin to take
over
• More shade
Primary Succession
• Medium sized animals and birds make this their
habitat.
• The vegetation grows closer together, reducing
the amount of space available for growing.
• Competition between lichen and shrubs for the
same space. Eventually one species (lichen) will
die out (or move) and the
other species will survive
(shrubs).
Primary Succession
• These plants die, and they add more
nutrients to the soil
• Shrubs and tress can survive now
Primary Succession
• Insects, small birds, and mammals have
begun to move in
• What was once bare rock now supports a
variety of life
http://p2-raw.greenpeace.org
Primary Succession
• These plants die, and they add more
nutrients to the soil
• Now larger trees can grow: Beech, Oak,
Walnut, Maple…
The Climax Community
• A climax community is a mature, stable community
that is the final stage of ecological succession. In an
ecosystem with a climax community, the conditions
continue to be suitable for all the members of the
community.
• Any particular region has its own set of climax
species, which are the plants that are best adapted
for the area and will persist after succession has
finished, until another disturbance clears the area.
6/5/03
M-DCC / PCB 2340C
20
These are Climax Communities
6/5/03
M-DCC / PCB 2340C
21
• Two main physical factors determine the nature of the
community that develops in an area. These are
temperature and the amount of rainfall.
• If we place the amount of rainfall on a graph’s “x”
axis, from 0-10, 10-20,and 20-30+ inches and the
temperature along the “y” axis from hot, moderate, to
cold, the various types of ecosystems will fit into the
graph based on the conditions that they require.
Temperature
Cold
Cold desert
Tundra
Taiga
Moderate
Temperate forest
Grassland
Deciduous forest
Hot
Hot desert
Savanna
Tropical forest
Rainfall (inches)
6/5/03
0-10
10-20
M-DCC / PCB 2340C
20-30+
22
Primary Succession
6/5/03
M-DCC / PCB 2340C
23
A summary of changes that occur during
succession:
• Pioneer species colonize a bare or disturbed site. Soil building.
• Changes in the physical environment occur (e.g., light,
moisture).
• New species of plants displace existing plants because their
seedlings are better able to become established in the changed
environment.
• Newly arriving species alter the physical conditions, often in
ways that enable other species to become established.
• Animals come in with or after the plants they need to survive.
• Eventually a climax community that is more or less stable will
become established and have the ability to reproduce itself.
6/5/03
M-DCC / PCB 2340C
24
• Disturbances will start the process of succession again.
What if?
What if?
• Ecosystem Fragmentation?
What if?
• An avalanche?
What if?
• Deforestation?
Threats to Climax Communities
• Forest Fires
• Humans building cities and roads (fragmenting
ecosystem)
• Clearing a community for agricultural purposes
• Deforestation
• Anything that destroys the existing community,
but much of the soil remains. Sometimes, some
of the organisms remain as well.
Secondary Succession
Secondary Seccession
Secondary Succession
• Organisms are destroyed but the soil is safe.
• The soil already contains the seeds of weeds,
grasses, and trees as well as nutrients. More
seeds are carried to the area by wind and birds.
• Succession begins again but the primary
species are different.
• Because soil is present, this succession is
faster.
Ecological Succession
•N
Secondary Succession on an
Abandoned Cornfield
Secondary Succession
• 1. Some seeds in the
soil begin to grow.
Secondary Succession
• Larger shrubs move in.
Secondary Succession
• 3. Fast growing trees
(such as pines) move
in
• 4. These are followed
by slower-growing
hardwood trees
http://www.ux1.eiu.edu
More Succession Resources
• Mt St. Helens after 30 years
https://www.youtube.com/watch?v=4RsMy
VavT2Q
• Succession Song
https://www.youtube.com/watch?v=rzE6B
NNLew0