© 2011 pearson education, inc. chapter 5 ecosystems: successions

© 2011 Pearson Education, Inc.

CHAPTER 5

Ecosystems: Successions


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


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


Recovery from fire


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


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


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


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


Primary succession on bare rock


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


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!!


If Primary succession is ... • On dry land…xenosene

• In water… hydrosene


Aquatic succession of a lake


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


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 weeds2. Small shrubs start to colonize3. Trees establish leading to climax community

Can take 70+ years


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


Secondary succession of an abandoned field


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


Iceland


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


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


Ground fire


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


Resilience in ecosystems


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


Late Successional Species• Tend to be persistent• Long-lived• Shade-tolerant• K-specialists• More competitive


“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.


SUCCESSION IN DUKE FORESTSUCCESSION IN DUKE FOREST


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


CHAPTER 5

Ecosystems:Energy, Patterns,and Disturbance

Active Lecture Questions


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.

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.

Review Question-1 Answer


True or False: Forest fires are destructive to ecosystems and should be avoided if at all possible.

a. Trueb. False

Review Question-2


True or False: Forest fires are destructive to ecosystems and should be avoided if at all possible.

a. Trueb. False



Resilience mechanisms might include

a. replenishment of nutrients.b. rapid regrowth of plant cover.c. succession in a forest.d. all of the above.

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.



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.

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.



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.

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.



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.

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.

Interpreting Graphs and Data-1 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.

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.

Interpreting Graphs and Data-2 Answer


All of the following are categories of consumers except

a. herbivores.b. photosynthesizers.c. omnivores.d. parasites.

Thinking Environmentally-1


All of the following are categories of consumers except

a. herbivores.b. photosynthesizers.c. omnivores.d. parasites.

Thinking Environmentally-1 Answer


Which of the following might be considered primary stakeholders in an ecosystem?

a. government decision makersb. scientists studying the ecosystemc. people living within the ecosystemd. conservation organizations

Thinking Environmentally-2


Which of the following might be considered primary stakeholders in an ecosystem?

a. government decision makersb. scientists studying the ecosystemc. people living within the ecosystemd. conservation organizations

Thinking Environmentally-2 Answer

© 2011 pearson education, inc. chapter 5 ecosystems: successions

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