Download Succession ppt

SUCCESSION
HOW DO ECOSYSTEMS
RESPOND TO CHANGE?
• A change in structure ensures a change in
function and species composition.
• Ecological succession is the gradual and
fairly predictable change in species
composition of an area over time.
• During succession, some species colonize
and their populations become more
numerous, whereas other species
populations decline and even disappear.
Succession in Volcanic Areas
• Krakatau – August 27, 1883 (Sundra Strait
between Sumatra and Java)
KRAKATAU
• 10:02 am explosion (100-150 megatons of TNT)
• The sound of the explosion traveled at the speed of
sound around the world 7 times.
• Blackened sky with showers of ash and heavy,
suffocating sulfur filled the sky and rained down on the
previous tropical rainforest ecosystem.
• Island collapsed causing a 40 meter high tsunami along
the shores of Java and Sumatra killing 40,000 people.
• Krakaktau had been replaced by an undersea crater 7
km long and 270 m deep.
• All traces of life were extinguished!
KRAKATAU
SUCCESSION OF KRAKATAU
• Rakata the southern
remnant of of
Krakatau survived
as a sterile obsidianlaced pumice island.
• Life quickly reestablished.
• Spiders “ballooned”
making their way to
the island “aeolian
plankton”
SUCCESSION OF KRAKATAU
• Other organisms that undergo long-distance dispersal as hitchikers
include: springtails, crickets, earwigs, barklice, bacteria, fungal
spores, nematode worms, and mites.
• Organisms that fly on their own include moths, butterflies,
dragonflies, true flies, beetles, birds, bats, and wasps.
• The monitor lizard and reticulated python swim.
• Rafting on logs and branches occurred by insects, snakes, frogs,
and small mammals.
• Waterspouts can pick up fish and transport them to lakes and
streams.
• Seeds pass through the guts of birds and mammals. Pioneer plants
(morning glory) and grasses moved in first, then Casuarina pine,
and now it is covered entirely by Asian rain forest, but NOT the
climax community that existed prior to the eruption.
• As the biodiversity of primary producers, so did the biodiversity of
the food web.
Primary Succession on a Newly
Established Volcanic Island
Primary
Succession –
involves the
gradual
establishment
of biologic
communities in
an area that
has not been
occupied by
life before.
SUCCESSION OF KRAKATAU
Secondary Succession on
Krakatau
Secondary Succession
– involves the reestablishment of a biotic
community in an area
where a biotic
community was
previously present.
Population Dynamics
• Population numbers are
becoming more stable a
Century after the eruption.
• The composition of the
populations are less stable.
• E.O. Wilson
“The thick green forests offers
testimony to the ingenuity and
resilience of life”
Primary Succession
• Lifeless area.
• Pioneer species (lichens and mosses) create
soil (chemical and physical weathering).
• Young soils support bacteria, fungi, insects, and
small worms (adds organic material to soil as
they die).
• Perennial grasses and herbs.
• All early successional plants grow low to the
ground, can establish large populations quickly
under harsh conditions.
Primary Succession
• After hundreds of years the soil matures
(deep and fertile) and midsuccessional
species grow.
• These species include: herbs, grasses,
and low shrubs and later include trees that
require lots of sunlight.
Primary Succession
• As midsuccessional stage species grow
and create shade areas they are replaced
by late successional species.
• Primary succession occurs fastest in
humid tropical areas and slowest in dry
polar areas.
Terrestrial Primary Succession
Boreal Forest Biome
Exposed rocks become
colonized by lichens and
mosses to create a soil. May
take hundreds to thousands of
years to establish a fertile soil
Small
herbs
and
shrubs
Heath
mat
Pine,
spruce
and
aspen
Climax
Community
Balsam fir,
paper birch,
white
spruce
Secondary Succession
• Occurs where soil or bottom sediment
remains where an area has been
disturbed or destroyed.
• Abandoned farmlands, burned or cut
forests, heavily polluted areas, land that
has been dammed or flooded.
Secondary Succession
Temperate Deciduous Forest Biome
Annual
Weeds
Perennial
weeds
and
grasses
Shrubs
Young Pine
Forest
Mature OakHickory Forest
Species Found at Various Stages
of Succession
Early Successional
Species
Midsuccessional
Species
Rabbit
Elk
Quail
Moose
Ringneck Pheasant
Deer
Dove
Ruffed grouse
Bobolink
Snowshoe hare
Pocket Gopher
Bluebird
Late
Successional
Species
Turkey
Martin
Hammond’s
flycatcher
Gray squirrel
Wilderness
Species
Grizzly bear
Wolf
Caribou
Bighorn Sheep
California condor
Great horned owl
Table 8-1 Ecosystem Characteristics at Immature and Mature Stages of Ecological Succession
Characteristic
Table 8-1
Page 158
Immature Ecosystem
(Early Successional Stage)
Immature Ecosystem
(Late Successional Stage)
Small
Large
Low
High
Mostly producers, few decomposers
Mixture of producers, consumers,
and decomposers
Ecosystem Structure
Plant size
Species diversity
Trophic structure
Ecological niches
Community organization
(number of interconnecting
links)
Few, mostly generalized
Many, mostly specialized
Low
High
Ecosystem Function
Biomass
Net primary productivity
Food chains and webs
Low
High
High
Low
Simple, mostly plant
with few decomposers
herbivore
Complex, dominated by
decomposers
Efficiency of nutrient recycling Low
High
Efficiency of energy use
High
Low
How Do Species Replace One
Another?
• 1. Facilitation – promotion of growth due natural
enrichment of soil.
• 2. Inhibition – early successional species can
hinder the establishment and growth of other
species. Removal of the inhibitors by fire,
bulldozer or other disturbance is the only way to
allow other species to establish.
• 3. Tolerance – late successional plants are
unaffected by plants at earlier stages.
What is the Role of Disturbance in
Succession?
• A disturbance is a discrete event in time that
disrupts an ecosystem or community.
• Natural disturbances = fires, hurricanes,
tornadoes, droughts, and floods.
• Anthropogenic disturbances = deforestation,
overgrazing, and plowing.
• Disturbances create openings for opportunistic
species to colonize areas and change the
community structure of an area.
Opportunistic Phragmites australis
What is the Role of Fire in
Succession?
• Fires start by lightening in the following
biomes: savanna, temperate grasslands,
chaparral, temperate rain forest, and
northern coniferous forest.
• Fire burns older trees by burning biomass
and releasing seeds as cones open in
intense heat = ensures regeneration.
Fire Suppression
• Fire suppression can be very dangerous.
It allows for the build up of large quantities
of flammable underbrush and
undergrowth.
• It allows conifers to grow very large and
store energy as biomass.
• BOTH contribute to fuel for the fire,
making a moderate forest fire catastrophic!
Forest Fires
After the Fire…
The Healthy Forest Restoration Act
• On December 3, 2003, President Bush signed into law the Healthy
Forests Restoration Act of 2003 to reduce the threat of destructive
wildfires while upholding environmental standards and encouraging
early public input during review and planning processes.
The Healthy Forests Restoration Act:
• Strengthens public participation in developing high priority forest
health projects;
• Reduces the complexity of environmental analysis allowing federal
land agencies to use the best science available to actively manage
land under their protection;
• Provides a more effective appeals process encouraging early public
participation in project planning; and
• Issues clear guidance for court action against forest health projects
The Healthy Forest Restoration Act
• Controversy – Is Bush just allowing
additional opportunity for logging
companies to come into forests and thin
them out to make money?
Is Succession Predictable?
• General patterns of succession are predictable.
• Research indicated that there is no ecological plan
leading to ecological balance or equilibrium.
• Succession can be highly variable, chaotic, and
unpredictable.
• We do know there will be changes to structure, function,
and species composition that will continue to change
over time due to facilitation, inhibition, and tolerance.
• The Earth’s ecosystems are dynamic and resilient.
Research shows that ecosystems with high diversity in
primary producers are the most resilient ecosystems.
Climax Community in Temperate
Deciduous Forest