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Ecosystems and Restoration Ecology

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Chapter 55 Ecosystems and Restoration Ecology – PowerPoint PPT presentation

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Title: Ecosystems and Restoration Ecology


1
Chapter 55
Ecosystems and Restoration Ecology
2
Overview
  • An ecosystem consists of all the organisms living
    in a community, as well as the abiotic factors
    with which they interact
  • Ecosystems range from a microcosm, such as an
    aquarium, to a large area such as a lake or
    forest
  • Regardless of an ecosystems size, its dynamics
    involve two main processes energy flow and
    chemical cycling
  • Energy flows through ecosystems while matter
    cycles within them

3
Energy, Mass, and Trophic Levels
  • Autotrophs build molecules themselves using
    photosynthesis or chemosynthesis as an energy
    source
  • Heterotrophs depend on the biosynthetic output of
    other organisms
  • Energy and nutrients pass from primary producers
    (autotrophs) to primary consumers (herbivores) to
    secondary consumers (carnivores) to tertiary
    consumers (carnivores that feed on other
    carnivores)

4
  • Detritivores, or decomposers, are consumers that
    derive their energy from detritus, nonliving
    organic matter
  • Prokaryotes and fungi are important detritivores
  • Decomposition connects all trophic levels

5
Figure 55.4
Sun
Key
Chemical cycling Energy flow
Heat
Primary producers
Primary consumers
Detritus
Microorganisms and other detritivores
Secondary and tertiary consumers
6
Energy and other limiting factors control primary
production in ecosystems
  • In most ecosystems, primary production is the
    amount of light energy converted to chemical
    energy by autotrophs during a given time period
  • (In a few ecosystems, chemoautotrophs are the
    primary producers)
  • The extent of photosynthetic production sets the
    spending limit for an ecosystems energy budget
  • (The amount of solar radiation reaching the
    Earths surface limits photosynthetic output of
    ecosystems only a small fraction of solar energy
    actually strikes photosynthetic organisms)

7
Ecosystems vary greatly in NPP and contribution
to the total NPP on Earth
  • Tropical rain forests, estuaries, and coral reefs
    are among the most productive ecosystems per unit
    area
  • Marine ecosystems are relatively unproductive per
    unit area, but contribute much to global net
    primary production because of their volume

8
Figure 55.6
Net primary production (kg carbon/m2?yr)
3
2
1
0
9
Nutrient Limitation
  • More than light, nutrients limit primary
    production in geographic regions of the ocean and
    in lakes
  • A limiting nutrient is the element that must be
    added for production to increase in an area
  • Nitrogen and phosphorous are typically the
    nutrients that most often limit marine production
  • Nutrient enrichment experiments confirmed that
    nitrogen was limiting phytoplankton growth off
    the shore of Long Island, New York

10
Figure 55.8
RESULTS
30 24 18 12 6 0
Ammonium enriched
Phosphate enriched
Unenriched control
Phytoplankton density (millions of cells per mL)
A
B
C
G
F
E
D
Collection site
11
  • The addition of large amounts of nutrients to
    lakes has a wide range of ecological impacts
  • In some areas, sewage runoff has caused
    eutrophication of lakes, which can lead to loss
    of most fish species (algal blooms)
  • In lakes, phosphorus limits cyanobacterial growth
    more often than nitrogen
  • This has led to the use of phosphate-free
    detergents

12
Eutrophication
  • The process by which a body of water acquires a
    high concentration of nutrients, especially
    phosphates and nitrates. These typically promote
    excessive growth of algae ? which depletes the
    water of oxygen and nutrients for other
    organisms.

Eutrophication often comes from runoff,
containing phosphorous and nitrogen from
fertilized soils contaminated water .
This has led to the use of phosphate-free
detergents!
13
An algal bloom or a red tide
An algal bloom or a red tide is a rapid
increase or accumulation in the population of
algae (typically microscopic) in an aquatic
system. These deplete oxygen and nutrients for
other organisms to survive! Some algal blooms add
toxins to the environment.
14
Primary Production in Terrestrial Ecosystems
  • In terrestrial ecosystems, temperature and
    moisture affect primary production on a large
    scale
  • Primary production increases with moisture

15
Energy transfer between trophic levels is
typically only 10 efficient
  • Secondary production of an ecosystem is the
    amount of chemical energy in food converted to
    new biomass during a given period of time

16
Trophic Efficiency and Ecological Pyramids
  • Trophic efficiency is the percentage of
    production transferred from one trophic level to
    the next
  • It is usually about 10, with a range of 5 to 20
  • Approximately 0.1 of chemical energy fixed by
    photosynthesis reaches a tertiary consumer
  • A pyramid of net production represents the loss
    of energy with each transfer in a food chain

17
  • In a biomass pyramid, each tier represents the
    dry weight of all organisms in one trophic level
  • Most biomass pyramids show a sharp decrease at
    successively higher trophic levels

18
Biological and geochemical processes cycle
nutrients and water in ecosystems
  • Life depends on recycling chemical elements
  • Nutrient circuits in ecosystems involve biotic
    and abiotic components and are often called
    biogeochemical cycles

19
Figure 55.14a
Movement over land by wind
Precipitation over land
Evaporation from ocean
Precipitation over ocean
Evapotranspira- tion from land
Percolation through soil
Runoff and groundwater
20
Figure 55.14b
CO2 in atmosphere
Photosynthesis
Photo- synthesis
Cellular respiration
Burning of fossil fuels and wood
Phyto- plankton
Consumers
Consumers
Decomposition
21
Figure 55.14ca
N2 in atmosphere
Reactive N gases
Industrial fixation
Denitrification
N fertilizers
Fixation
Runoff
Dissolved organic N
NO3
NO3
NH4
Terrestrial cycling
Aquatic cycling
Decomposition and sedimentation
22
Figure 55.14cb
Terrestrial cycling
N2
Denitri- fication
Assimilation
Decom- position
NO3
Uptake of amino acids
Fixation in root nodules
Ammonification
Nitrification
NH3
NO2
NH4
23
Decomposition and Nutrient Cycling Rates
  • Decomposers (detritivores) play a key role in the
    general pattern of chemical cycling
  • Rates at which nutrients cycle in different
    ecosystems vary greatly, mostly as a result of
    differing rates of decomposition
  • The rate of decomposition is controlled by
    temperature, moisture, and nutrient availability

24
  • Rapid decomposition results in relatively low
    levels of nutrients in the soil
  • For example, in a tropical rain forest, material
    decomposes rapidly and most nutrients are tied up
    in trees other living organisms
  • Cold and wet ecosystems store large amounts of
    undecomposed organic matter as decomposition
    rates are low

25
Case Study Nutrient Cycling in the Hubbard Brook
Experimental Forest
  • The Hubbard Brook Experimental Forest (White
    Mountain National Forest, New Hampshire) has been
    used to study nutrient cycling in a forest
    ecosystem since 1963
  • The research team constructed a dam on the site
    to monitor loss of water and minerals
  • They found that 60 of the precipitation exits
    through streams and 40 is lost by
    evapotranspiration
  • In one experiment, the trees in one valley were
    cut down, and the valley was sprayed with
    herbicides

26
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27
  • Net losses of water were 30?40 greater in the
    deforested site than the undisturbed (control)
    site
  • Nutrient loss was also much greater in the
    deforested site compared with the undisturbed
    site
  • For example, nitrate levels increased 60 times in
    the outflow of the deforested site
  • These results showed how human activity can
    affect ecosystems

28
Figure 55.16c
80 60 40 20
Deforested
Nitrate concentration in runoff (mg/L)
Completion of tree cutting
4 3 2 1 0
Control
1965
1966
1967
1968
(c) Nitrate in runoff from watersheds
29
Effects of habitat loss
  • DEFORESTATION
  • The cutting down of trees causes several
    ecological effects
  • 1 Without the trees to absorb the water, much
    of the minerals (particularly nitrogen) is lost
    in the soils from the runoff.
  • 2- With the loss of plant life, less carbon
    dioxide is absorbed (through photosynthesis)
    making higher levels of CO2 in the atmosphere,
    contributing to global warming!
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