Changes in the ecosystem
SUCCESSION
Changes
occur all the time in
an ecosystem. Trees die and
new trees take their place.
Young animals are born as the
older ones die.
As
long as there are not major
disturbances the ecosystem
will remain essentially the
same.
The
natural stability of an
ecosystem keeps it from
undergoing major changes is
called homeostasis.
SUCCESSION
It’s
important to understand
the changes in an ecosystem so
that we can understand how
the ecosystem will react to the
changes that human activity
tends to bring about.
VOCABULARY
Pioneer
species: the first
species to appear during the
process of succession, usually
mosses, lichens, grasses &
weeds.
Climax
community: the stable
mature community
SUCCESSION
Succession
is the process of
community development over
time.
A
mature community will still
change but its overall
appearance will remain the
same.
PRIMARY SUCCESSION
 change
in species over time that
has not been inhabited by organisms.
starts from bare rock.
Lichens are the most
important element in the initial
community called the
pioneer community.
 Lichens
are important early
pioneer species. Lichen is a
species of alga and fungi that live
together in a symbiotic relationship.
Lichens
secrete an acid that
breaks down the rock to begin
soil formation.
If
the process of succession
occurs without any
disturbances, the species will
form the climax community.
This is the last stage of
succession
Each
biome has its own climax
community. The climax
community for PA is the oakhickory forest as well as the
beech, hemlock & maple forest
of Northern PA forest.
SECONDARY SUCCESSION
change in species composition and
ecosystem overtime already within
a pre-existing community.

Some
animals can survive all
stages of secondary
succession. Most animals
appear only in certain stages
and disappear with others.
EXAMPLES OF SECONDARY
SUCCESSION
1. Abandoned farms
2. Burned or cut forests
3. Heavily polluted streams
4. Areas affected by flood
waters.
FIRE MAINTAINED COMMUNITIES
 Fires
can be set by lightning,
storms or human activity. Burned
areas undergo secondary
succession.
Some
communities are immune
to fire. For example, the
lodgepole pine tree needs
temperatures of above several
hundreds degrees to
germinate their seeds.
Serotinous
is an ecological
adaptation exhibited by some
seed plants, in which seed
release occurs in response to
an environmental trigger,
rather than spontaneously at
seed maturation. Best trigger
is fire.
ECOSYSTEM DISTURBUANCES
A
disturbance can change an
ecosystem both physically &
biologically.
Disturbances
can be natural or
due to human actions.
Repeated
disturbances will
prevent an area from returning
to its climax community.
NATURAL DISTURBANCES
1. Volcanic eruptions
2. Tornadoes
3. Hurricanes
4. Floods/Drought
5. Natural Wildfires
Now…read
partner.
the chart with a
HUMAN DISTURBANCES
1.
2.
3.
4.
5.
Man started fire
Land development
Mining
Farming
Over hunting
YELLOWSTONE FIRE 1988
INVASIVE SPECIES
Invasive
species is a nonnative
organism that spread widely in
a community.
Invasive
species are one type
of community disturbance and
a major problem in many parts
of the world.
Invasive
species become a
problem when there are no
limiting factors such as
predators, parasites, or
competitors.
EXAMPLES
Zebra
mussels
Kudzo…
Invasive species in Washington
State