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CHAPTER 5
Ecosystems:
Successions
© 2011 Pearson Education, Inc.
Introduction to ecosystems
• In 1988, lightning started fires in Yellowstone
National Park
• 165,000 acres were burned
• National Park Service policies have changed over
time
• In the early years, all fires were extinguished
• Before 1988, only fires that threatened human
habitations were extinguished
• This fire started a great controversy over this policy
• Snow in September finally put the fires out
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Yellowstone recovered from the 1988
fire
• The fires burned 36% of the park
• Burned and unburned areas were interspersed
• Within 2 weeks, grasses and other vegetation
sprouted
• Within a year, vegetation covered the burned areas
• Bison and elk fed on the new vegetation
• Within 25 years, plant and animal diversity will have
completely recovered in the burned areas
• Fire is vital to many ecosystems
• It may even impact evolution
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Recovery from fire
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Characteristics of ecosystems
• Yellowstone National Park (founded in 1872) is part
of the Greater Yellowstone Ecosystem
• Because of its unique features, it is a World Heritage
Site and International Biosphere Reserve
• Ecosystems contain communities of interacting
species and their abiotic factors
• They function on different scales
• It’s hard to delineate fixed boundaries
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Ecosystem responses to disturbance
• Natural ecosystems operate in dynamic, changing
ways
• The landscape comprises a shifting mosaic of
patches
• Disturbance: a significant change that kills or
displaces many community members
• Ecological succession: transition from one biotic
community to another (called seral stages)
• Pioneer species: colonize a newly opened area first
• Species can create conditions favorable to other
species and less favorable to them
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Succession does not go on indefinitely
• Facilitation: driving succession forward by
improving conditions for subsequent species
• Climax ecosystem: the assemblage of species
continues on in space and time
• Even these communities experience change if new
species are introduced or old ones are removed
• Patches of disturbance open space for new growth
• Fire-adapted ecosystems: some biomes (e.g.,
prairies) undergo succession to other stages
without periodic fires
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Primary succession
• Primary succession: the process of initial invasion
and progression from one biotic community to
another
• In an area lacking plants and soil (e.g., a retreating
glacier, exposed sand bar, after lavaflow)
1. Mosses exploit bare rock
•
•
•
•
Their spores lodge in cracks
Moss grows and forms mats that trap soil particles
Seeds of larger plants lodge in the moss mats
Eventually, enough soil is trapped to support shrubs
and trees
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Primary succession on bare rock
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Primary Succession
• Initial establishment of an ecological
community on previously unoccupied site
Exposed sandbar
Newly cooled lava
New Sand Dune
Also: surface mined area (w/o topsoil), sunken ships
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Primary Succession
• 2. species diversity increases. Invertebrates begin
to live in soil, weathering adds nutrients. Increases
humus and water holding capacity. Pioneer species!
• 3. competition. Larger plants increase so sun, wind,
temp less extreme. K-strategists take hold, r can’t
compete
• 4. fewer new species colonize. Late colonizers
establish, shading out early colonizers, complex food
webs develop, K-strategists have specialized niches
Seral Climax-dynamic equilibrium. Max possible
development
Can take 1000s of years!!
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If Primary succession is ...
• On dry land…xenosene
• In water… hydrosene
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Aquatic succession of a lake
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Hydrosene succession
• Natural succession also takes place in lakes and
ponds
• Soil particles erode from the land and enter the
water
• Aquatic vegetation provides detritus that also fills the
pond or lake
• Terrestrial species advance and aquatic species
move further into the lake
• The climax ecosystem can be a bog or forest
• Disturbances (e.g., drought, flood) can send
succession back to an earlier stage
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Secondary succession
• Secondary succession: an area cleared by some
disturbance (fire, floods, humans) is reinvaded by
plants and animals from surrounding areas
• Starts with pre-existing soil
• 1. Crabgrass invades an abandoned agricultural
field
• It is shaded out by taller grasses and weeds
2. Small shrubs start to colonize
3. Trees establish leading to climax community
Can take 70+ years
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Secondary Succession
• On previously occupied sites that have been
disturbed
• Remnants of the previous community site
contribute to recolonization.
Old Farms, Pastures
Logged Areas
Areas destroyed by
natural disaster
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Secondary succession of an
abandoned field
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Disturbance and resilience
• For succession to occur, plants and animals must
already be present in the area
• All stages of succession are present in any
landscape
• Disturbances constantly create gaps or patches
• Biodiversity is enhanced by disturbance
• Natural succession can be blocked or modified if
species have been eliminated
• Forests in Iceland were eliminated
• Regeneration was prevented due to a lack of seeds
and the presence of grazing sheep
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Iceland
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Fire and succession
• Fire is a major form of disturbance
• Decades ago, forest managers thought all fire
was bad
• But pine forests were replaced with economically
worthless broad-leaved trees
• Accumulated deadwood allowed insects to attack
trees
• Different species have different tolerances to fire
• Grasses and pines tolerate fire
• Broad-leaved trees are damaged by fire
• Fire releases nutrients
• Some plants need fire to germinate
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Fire climax ecosystems
• Fire climax ecosystems: ecosystems that depend on
fire to maintain their existence (e.g., grasslands, pine
forests)
• Fire can be a tool in ecosystem management
• With regular fire, deadwood doesn’t accumulate
• Crown fires are also natural
• They clear sick or dead trees and release nutrients
• The meadows they create support higher biodiversity
• Logging encourages large fires
• Removes larger, resistant trees and leaves dead
branches
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Ground fire
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Resilience
• Resilience: the ability of an ecosystem to return to
normal functioning after a disturbance
• Helps maintain ecosystem sustainability
• Resilience mechanism: the processes of
replenishment of nutrients, dispersion by plants and
animals, regrowth of plants
• Resilience has its limits
• A badly degraded ecosystem can’t carry out its
original functions
• A new, less productive ecosystem is created
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Resilience in ecosystems
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Pioneer Species
• Early successional species
• Rapidly growing, short lived
• Widely and rapidly disperse
(wind)
• Do well in full sun
• “opportunistic”
• often involved in facilitation
• r-specialists
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Late Successional Species
•
•
•
•
•
Tend to be persistent
Long-lived
Shade-tolerant
K-specialists
More competitive
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“Balance of Nature” doesn’t exist
• Late successional stages may exist for many
human generations and changes may not be
evident
• Climates are not stable, and communities
change as climate changes.
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SUCCESSION IN DUKE FOREST
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Started as farmland…
• Much of Duke Forest was abandoned farmland at
the time of its purchase during the depression
• Over-worked and eroded by the effects of wind and
rain, the soils had lost many of the life-giving
nutrients necessary for the survival of healthy crops
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CHAPTER 5
Ecosystems:
Energy, Patterns,
and Disturbance
Active Lecture Questions
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Review Question-1
The process of initial invasion and progression
from one biotic community to the next is called
a. primary succession.
b. secondary succession.
c. a climax ecosystem.
d. fire.
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Review Question-1 Answer
The process of initial invasion and progression
from one biotic community to the next is called
a. primary succession.
b. secondary succession.
c. a climax ecosystem.
d. fire.
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Review Question-2
True or False: Forest fires are destructive to
ecosystems and should be avoided if at all
possible.
a. True
b. False
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Review Question-2 Answer
True or False: Forest fires are destructive to
ecosystems and should be avoided if at all
possible.
a. True
b. False
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Review Question-3
Resilience mechanisms might include
a. replenishment of nutrients.
b. rapid regrowth of plant cover.
c. succession in a forest.
d. all of the above.
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Review Question-3 Answer
Resilience mechanisms might include
a. replenishment of nutrients.
b. rapid regrowth of plant cover.
c. succession in a forest.
d. all of the above.
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Review Question-4
When an ecosystem reaches a dynamic
balance between all of the species and the
physical environment, the ecosystem is
considered
a. at climax.
b. in primary succession.
c. in secondary succession.
d. in aquatic succession.
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Review Question-4 Answer
When an ecosystem reaches a dynamic
balance between all of the species and the
physical environment, the ecosystem is
considered
a. at climax.
b. in primary succession.
c. in secondary succession.
d. in aquatic succession.
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Review Question-5
A small human action that catalyzes a major
change in the state of an ecosystem is called
the
a. turning point.
b. dew point.
c. tipping point.
d. point of no return.
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Review Question-5 Answer
A small human action that catalyzes a major
change in the state of an ecosystem is called
the
a. turning point.
b. dew point.
c. tipping point.
d. point of no return.
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Interpreting Graphs and Data-1
According to Fig. 5-11, the temperature and
precipitation of the moist tundra biome can be
described as
a. cold and wet.
b. cold and dry.
c. hot and wet.
d. hot and dry.
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Interpreting Graphs and Data-1 Answer
According to Fig. 5-11, the temperature and
precipitation of the moist tundra biome can be
described as
a. cold and wet.
b. cold and dry.
c. hot and wet.
d. hot and dry.
© 2011 Pearson Education, Inc.
Interpreting Graphs and Data-2
According to Fig. 5-20, areas shaded in black
have
a. no net primary
production.
b. low net primary
production.
c. medium net
primary production.
d. high net primary
production.
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Interpreting Graphs and Data-2 Answer
According to Fig. 5-20, areas shaded in black
have
a. no net primary
production.
b. low net primary
production.
c. medium net
primary production.
d. high net primary
production.
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Thinking Environmentally-1
All of the following are categories of consumers
except
a. herbivores.
b. photosynthesizers.
c. omnivores.
d. parasites.
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Thinking Environmentally-1 Answer
All of the following are categories of consumers
except
a. herbivores.
b. photosynthesizers.
c. omnivores.
d. parasites.
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Thinking Environmentally-2
Which of the following might be considered
primary stakeholders in an ecosystem?
a. government decision makers
b. scientists studying the ecosystem
c. people living within the ecosystem
d. conservation organizations
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Thinking Environmentally-2 Answer
Which of the following might be considered
primary stakeholders in an ecosystem?
a. government decision makers
b. scientists studying the ecosystem
c. people living within the ecosystem
d. conservation organizations
© 2011 Pearson Education, Inc.