Transcript Chap20 - Dr. Mark Pyron

SUCCESSION AND STABILITY
Chapter 20
Molles: Ecology 2nd Ed.
Chapter Concepts
•
What is succession?
•
What are the causes of succession?
•
How do community composition / diversity, and
ecosystem energy flow / nutrient cycling change
during succession?
•
How do ecologists know this stuff?
•
What are the implications in a human –
dominated world?
Molles: Ecology 2nd Ed.
•
What does it take to keep this lawn
looking like this?
What will happen to this lawn over time with
no human intervention?
Molles: Ecology 2nd Ed.
Primary Succession
•
Establishment of a biological community on
new substrates where no community had
previously existed.
•
Examples
 On land exposed by retreating glaciers
 On new substrates created by volcanic
lava flows
Molles: Ecology 2nd Ed.
Primary Succession – Glacier Bay, Alaska
•
Reiners et.al. (1971)
 Changes in plant diversity during
succession
Molles: Ecology 2nd Ed.
Molles: Ecology 2nd Ed.
Molles: Ecology 2nd Ed.
Molles: Ecology 2nd Ed.
Glacier Bay Succession
Shrubs
Aspen
Bare
Lichens
rock & Mosses
soil
Grasses
Forbs
Soil Development
Molles: Ecology 2nd Ed.
White
spruce
Increasing Vertical
Structure
Black
spruce
Coral Reef Succession On Lava Flows
Lava Flow From Land Into Sea
Molles: Ecology 2nd Ed.
Coral Reef Succession On Lava Flows
Underwater Lava Flow
Molles: Ecology 2nd Ed.
Coral Reef Succession On Lava Flows
Molles: Ecology 2nd Ed.
Coral Reef Succession On Lava Flows
Molles: Ecology 2nd Ed.
Coral Reef Succession On Lava Flows
Molles: Ecology 2nd Ed.
Coral Reef Succession On Lava Flows
Molles: Ecology 2nd Ed.
Coral Reef Succession On Lava Flows
Molles: Ecology 2nd Ed.
Coral Reef Succession On Lava Flows
Molles: Ecology 2nd Ed.
Secondary Succession
•
Re-building of a biological community after a
previously existing community is destroyed by a
disturbance, but the soil remains.
•
Examples:
 Recovery of forests after fire, wind storm, insect
pest outbreak, logging
 Re-growth of natural vegetation after farmland
abandonment
Molles: Ecology 2nd Ed.
Old Field Succession
Molles: Ecology 2nd Ed.
Old Field Succession
1 Year After Abandonment
Grasses and Weeds Dominate
Molles: Ecology 2nd Ed.
Old Field Succession
5 Years After Abandonment
Goldenrod and Other Perennial Weeds Dominate
Molles: Ecology 2nd Ed.
Old Field Succession
10 Years After Abandonment
Tree saplings and shrubs
begin to establish
Molles: Ecology 2nd Ed.
Old
Field
Succession
20 Years After
Abandonment
Trees and shrubs
begin to replace
herbaceous plant
species
Molles: Ecology 2nd Ed.
Old Field Succession
28 Years After Abandonment
Where Did the Grasses and Goldenrod Go ?
Molles: Ecology 2nd Ed.
Definitions
•
Climax Community –
 Late successional community
 Remains stable until disrupted by
disturbance
Molles: Ecology 2nd Ed.
Primary vs. Secondary Succession
•
Primary succession slower than secondary
succession.

With no pre-existing seeds or root systems
in the soil, establishment of organisms
requires migration into the area from other
locations.

Establishment of many plant species is
delayed until soil development has occurred
(sand, silt, clay, organic matter)
Causes of Succession
•
Species differ in dispersal (migration)
ability.
•
Species differ in their environmental
tolerances / requirements.
•
Species differ in growth rate.
•
Species differ in life span.
•
Species differ in competitive ability.
Pioneer (r-selected) Species
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Produce large numbers of small, easily
dispersed young.
•
Are usually first species to arrive after
disturbance.
•
Grow fast in high resource environment.
•
Tolerate harsh physical environments.
•
Reach sexual maturity fast.
•
Short life spans (require replacement via
reproduction to remain on the site)
•
Poor competitive ability.
Late-Succession (K-selected) Species
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Produce fewer, larger young that often have
limited dispersal from parent.
•
Usually arrive at disturbed site later (may
require pioneers moderate environment first).
•
Have slower growth rate.
•
Longer time to sexual maturity.
•
Long-lived (hold onto space / resources)
•
Good competitive ability (able to displace
pioneer species)
Community and Ecosystem Changes During
Succession
•
Species Diversity increases (but may decrease
during late stages due to competitive
exclusion).
•
Net Primary Production increases during early
stages, but declines during late stages due to
increased respiration.
•
Nutrient Cycling / Retention greatest during
middle stages.
Species Richness During Primary Succession at
Glacier Bay Study Plots
Fig 20.2
Change of Plant Growth Forms During Succession
Fig 20.3
Woody Plant Species Richness During Secondary
Forest Succession (Eastern USA)
Piedmont Plateau
Molles: Ecology 2nd Ed.
Woody Plant Species Richness During Secondary Forest
Succession (Eastern USA)
Fig 20.4
Breeding Bird Species Richness During Secondary Forest
Succession (Eastern USA)
Fig 20.5
Species Richness of Macroinvertebrate and Macroalgae
Species During Secondary Succession on Intertidal Boulders
Fig 20.7
Algal species Diversity During Secondary Succession in
Sycamore Creek After Flooding
Fig 20.8
Fig 20.8
Fig 20.9
Molles: Ecology 2nd Ed.
How Do We Study Succession ?
(Long-Term Research)
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1. Establish permanently marked plots in an area recently
affected by disturbance.
•
2. Record community / ecosystem variables

Species relative abundance / Species diversity

Biomass / Net Primary Production

Nutrient Pools and Input / Output Fluxes
How Do We Study Succession ?
(Long-Term Research)
•
3. Re-measure variables in exactly the same plots at
different times (often intervals of decades).
•
4. Change in community / ecosystem variables over time
attributed to succession.
Molles: Ecology 2nd Ed.
How Do We Study Succession ?
(Space-for-Time Comparative Studies)
•
1. Record community / ecosystem variables in plots
established in different areas that were disturbed at
different times in the past.

Species relative abundance / Species diversity

Biomass / Net Primary Production

Nutrient Pools and Input / Output Fluxes
How Do We Study Succession ?
(Space-for-Time Comparative Studies)
2. Compare community / ecosystem variables between these
different areas. Differences are attributed to succession.
•
•
3. Valid only if the following conditions are true:
Different areas were all disturbed in exactly the same way

Different areas have similar environmental conditions

Molles: Ecology 2nd Ed.
How Do Disturbance Characteristics Influence
Succession?
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Short Return Time (High Frequency)




•
Limits opportunity for immigration of species
and re-growth of populations.
K-selected species eliminated.
Limits opportunity for re-building biomass.
Nutrient losses due to disturbance not fully
replenished before next disturbance.
Community dominated by r-selected species, with low
standing crop biomass and low nutrient availability.
How Do Disturbance Characteristics Influence
Succession?
•
Large Magnitude + High Intensity
 Re-establishment of species populations requires longdistance migration from undisturbed areas.
 Succession is retarded by slow immigration rate.
 NPP recovers slowly
 Biomass pool recover slowly
 Nutrient losses greater during slow recovery
•
Community dominated by r-selected species, with rapid
dispersal ability for a longer period.
How Do Disturbance Characteristics Influence
Succession?
•
Small Magnitude or Low Intensity
 Re-establishment of species populations from
surviving individuals within / near disturbed area.
 Succession proceeds quickly.
 NPP recovers rapidly.
 Biomass pool recover rapidly.
 Nutrient losses quickly stop.
•
Community dominated by species that are best able
survive disturbance and compete for limited growing
space (K-selected).
Implications for Human Activities
•
Human populations typically increase the
frequency, magnitude, and intensity of
disturbance.

Entire landscapes dominated by r-selected
species b/c succession never finishes before
next disturbance.

Depletion of biomass, soil organic matter,
and nutrient pools.
Implications for Human Activities
•
Humans sometimes suppress disturbances
(e.g. fire), increasing return time, but often with
increase in magnitude and intensity.

Entire landscapes become dominated by Kselected species, and accumulate biomass.

Communities may become more susceptible
to catastrophic disturbance (e.g., recent fires
in western U.S.)
Effects of Fire Suppression
Eastern Hardwood Forest
35
Oak
Number of Trees
of trees
Number
30
25
Maple
Sassafras
Dogwood
Fire Suppression
Begins
20
15
10
5
0
1900 1910 1920 1930 1940 1950 1960 1970
▲
Logging
Year of Tree Establishment
Effects of Fire Suppression
Western Conifer Forests
1600
Number of
trees
ofTrees
Number
1400
1200
1000
Ponderosa Pine
White Pine
Other
Fuel build-up leads to
catastrophic crown fire
800
600
400
200
Fire Suppression
Begins
Frequent LowIntensity Fires
▼▼▼▼▼▼▼▼
0
1980 1960 1940 1920 1900 1880 1860 1840 1820 1800 1780
Year of Establishment
Implications for Human Activities
•
Humans depend on rapid growing, r-selected
species for agriculture and forestry.

Humans use disturbance to prevent
succession and maintain open environments
required by these pioneer species.

Frequent human disturbance to maintain
crop species can deplete soil organic matter
and nutrient pools.
The End
Molles: Ecology 2nd Ed.