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CHAPTER 4
ECOSYSTEMS AND HOW
THEY WORK
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Ecology and Life
Ecology is study of how organisms interact
with one another and with their nonliving
environment
A species consists of all organisms -living
things-which can reproduce living offspring
Populations consist of organisms of same
species living in same place at same time
Genetically diverse organisms contribute
genes to the populations gene pool
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Ecology and Life -2
Several interacting populations occupying
the same habitat form a community
An ecosystem is the communities and their
nonliving environment; all Earths
ecosystems form the ecosphere
What are 6 characteristics of living thingsthat enable growth, survival and
reproduction?
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Reproduction and Evolution
While asexual reproduction can produce
new offspring - they are all identical
Sexual reproduction produces organisms
have new combinations of parental traits.
Traits which offer a better chance of
survival are adaptive and lead to evolution
Biodiversity refers to all of the variety of
living organisms and their traits
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Earths Life-support Systems
Atmosphere consists of inner trophosphere
and outer stratosphere
Hydrosphere is liquid, solid & gaseous
water
Lithosphere is crust and upper mantle
Ecosphere is portion of earth where
organisms interact (atmosphere,
hydrosphere, and upper lithosphere)
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Sustaining Life on Earth
Interconnected factors include:
one-way flow of high quality energy from sun;
What is the path?
Cycling of matter or nutrients through
ecosphere
Gravity permits earth to hold onto all parts ofecosphere
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Life is Sustained by Sun
Sunlight supplies energy for photosynthesis
Solar energy powers cycling of matter
Solar energy drives climate and weather
systems
Hydrogen and helium nuclei fuse releasing
solar energy
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Effects of Solar Radiation
Solar energy reaching earth is either
reflected (28%) or absorbed (28%)
Absorbed radiation warms, evaporated,
cycles, and generates winds.
Less than 1% is captured for photosynthesis
these reactions produce all organic
compounds required for all living organisms
Greenhouse effect - ultimate change of all
solar radiation to heat (infrared radiation)
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Ecosystem Concepts
Biomes are large terrestrial regions
characterized by distinct climate and
specific life forms.
Climate is weather - over the long term; it
determines type of life forms in biomes
Biomes contain many ecosystems
Aquatic life zones (like biomes) consist of
freshwater and marine life zones
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Major Components of Ecosystems
Abiotic - nonliving; water, air, nutrients and
solar energy
physical factors affecting terrestrial ecosystems
What are the six factors listed?
Physical factors affecting aquatic ecosystems
What are three factors listed?
Biotic - living componentsObserve how abiotic and biotic components
interact (fig. 4.9 and 4.10)
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Tolerance
Each population has range of variations in
environmental factors that it can tolerate; the
extremes of the range of tolerance are
tolerance limits.
Within this range of tolerance are variety of
conditions which are optimal for success.
State the law of tolerance
Some factors limit population growth more
than others - Name limiting factors in terrestrial and
aquatic ecosystems
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Biotic Components of Ecosystem
Producers (autotrophs) transform solar
energy into chemical energy of bonds of
organic molecules - Photo (&chemo)synthesisgreen plants and aquatic phytoplankton
Consumers (heterotrophs) cannot synthesize
organic molecules from scratch - they canconvert organic molecules from food to
other organic molecules needed
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Consumers
Consumers (heterotrophs) obtain energy
and nutrients from other organisms
Herbivores - primary consumers
Secondary & tertiary consumers may be:
carnivores - meat-eaters
omnivores - plant and meat eaters
scavengers and detritus feeders feed on animalsalready killed or remains of such
Decomposers - recycle organic molecules and
release inorganic molecules - biodegradation
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One-way Flow of Energy
Respiration is release of energy from
chemical bonds of organic molecules
Aerobic (w/oxygen) respiration --> complete
breakdown of glucose to CO2 + water +energy
Anaerobic (w/out oxygen) respiration (also
called fermentation) --> incomplete breakdown
of glucose --> methane, alcohol or acetic acid
One-way flow of energy through organisms
Matter & energy recycles through ecosystems
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Food Chains
Food chain - how nutrients and energy
move through organisms in ecosystem -
who eats who (Fig. 4-14)trophic levels begin with producers and end
with decomposers
Be sure you can identify types of organisms ateach trophic level, I.e. producers, primary,
secondary, and tertiary consumers
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Food Webs
Food web - network of interconnected food
chains; more complex because one
organism is never eaten by only one other Identify the various trophic levels shown in
Fig. 4.15
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Energy flow and Biomass storage
Biomass (dry weight of organic matter) is
transferred between trophic levels - but at
each level some biomass changes to energy
and is lost
Ecological efficiency compares biomass
transferred to that converted and lost
Pyramid of energy flow shows that firsttrophic level has greatest amount of energy
- some is transferred and some is lost at
each level
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Pyramid of Biomass
This pyramid demonstrates the total amount
of biomass at each trophic level
Why is biomass of producers less than thatof primary consumers in ocean ecosystem?
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Pyramid of Numbers
The actual number of organisms at each
trophic level - regardless of size (amount of
energy or biomass contained) Numbers of organisms at first level often
greatest and fourth level often has least
number of organisms - unless the producersindividually contain more biomass
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Primary Productivity
Gross Primary productivity - rate at which
producers convert solar energy into
chemical energy
Net Primary productivity - accounts forenergy that produces use for their own
respiration - biomass lost - so this rate is
always less Net primary productivity determines
carrying capacity of species in ecosystems
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Comparisons of net productivity
Which life zones have the greatest net
productivity? Why zones have the least?
Though tropical rain forest have highproductivity for natural plants, the
productivity when cleared is much less.
What effect have humans had on the earthsnet productivity?
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Matter Cycling in Ecosystems
Nutrients are any atoms, ions or molecules
needed by organisms to live, grow or
reproduce. Nutrient cycles (biogeochemical cycles)
show how elements needed in greatest
amounts travel through ecosystems
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Hydrologic (water) Cycle
Main processes:evaporation -liquid water to water vapor
transpiration - evaporation from plants
condensation - water vapor to liquid water
precipitation - water from air goes to land
infiltration - water moves into soil
percolation - water flows downward throughsoil
runoff - water flows downward across surface
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Hydrologic Cycle -2
Cycle powered by solar energy and gravity
Water vapor measurements: absolute vs.
relative humidity
Condensation requires condensation nuclei
and occurs at dew point
How does surface runoff affect lithosphere?
Name three ways Man has intervened in
water cycle.
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Carbon Cycle
Earths temperature varies with changes in
carbon dioxide in atmosphere and water
Producers use CO2 from atmosphere for
photosynthesis
Consumers release CO2 to atmosphere
Carbon of buried organisms may become
fossil fuels
Most carbon stored as limestone and in
water - How has Man disturbed carbon cycle?
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Nitrogen Cycles
Most is in gas form in atmosphere
Gaseous nitrogen must be fixed to form
ammonia or nitrates for plant assimilation
Plants synthesize nitrogen-containing
organic molecules -proteins & nucleic acids
Ammonia and nitrates converted back to gaswhich reenters atmosphere
How has Man intervened in nitrogen cycle?
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Phosphorus Cycle
There is no gaseous phase for phosphorus
Phosphorus circulates through water, earths
crust and living organisms
Phosphorus is added to land naturally by
guano and artificially by fertilizer
Phosphorus is limiting factor in growth ofmany organisms
How has Man intervened in phosphorus cycle?
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Sulfur Cycle
Much sulfur stored underground in rocks
and minerals
Sulfur enters atmosphere as hydrogensulfide, sulfur dioxide and sulfates
Water combines with sulfur dioxide to form
acid rain How has Man increased the atmospheric
phase of the sulfur cycle?
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Ecological Research
Field research - dirty, difficult and
expensive, but important; new technologies
Laboratory research - set up modelecosystems with controlled variables; easier
but must be coupled with field research
Systems analysis - computer simulationsused to make prediction; accuracy depends
on input
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Ecosystem Services and
Sustainability Ecosystem services constitute earths
natural capital; one is biological diversity:
genetic diversity - individuals in species vary ingenetic makeup
species diversity - habitats contain wide variety
of different species
ecological diversity - ecosystems contain wide
variety of communities
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Ecosystem Services and
Sustainability -2 Ecosystem services provide recycling,
purification and natural pest control
Each species results from many adaptations
Each species provides raw material for
future adaptation
Two basic principles of natural ecosystemsustainability: use renewable solar energy
and recycle nutrients efficiently