Transcript Chapter 34: Ecosystems and Human Interferences

Chapter 34: Ecosystems and
Human Interferences
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The Nature of Ecosystems
An ecosystem contains biotic (living)
components and abiotic (nonliving)
components.
The biotic components of ecosystems
are the populations of organisms.
The abiotic components include
inorganic nutrients, water, temperature,
and prevailing wind.
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Biotic Components of an
Ecosystem
Autotrophs are producers that produce
food for themselves and for
consumers.
Most are photosynthetic organisms but
some chemosynthetic bacteria are
autotrophs.
Heterotrophs are consumers that take in
preformed food.
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Biotic components
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Consumers may be:
Herbivores – animals that eat plants,
Carnivores – animals that eat other
animals,
Omnivores, such as humans, that eat
plants and animals, or
Decomposers, bacteria and fungi, that
break down dead organic waste.
Detritus is partially decomposed organic
matter in the soil and water; beetles,
earthworms, and termites are detritus
feeders.
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Consumers
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Energy Flow and Chemical
Cycling
Every ecosystem is characterized by two
phenomena:
1) Energy flows in one direction from the
sun to producers through several
levels of consumers, and
2) Chemicals cycle when inorganic
nutrients pass from producers
through consumers and returned to
the atmosphere or soil.
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Nature of an ecosystem
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Only a small portion of energy and
nutrients made by autotrophs is passed
on to heterotrophs, and only a small
amount is passed to each succeeding
consumer; much energy is used at
each level for cellular respiration and
much is lost as heat.
Ecosystems are dependent on a
continual supply of solar energy.
The laws of thermodynamics support the
concept that energy flows through an
ecosystem.
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Energy balances
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Energy Flow
The feeding relationships in an
ecosystem are interconnected in a
food web.
Generally, the upper portion of a food
web is a grazing food web, based on
living plants, and the lower portion is a
detrital food web, based on detritus and
the organisms of decay.
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Forest food webs
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Trophic Levels
A trophic level is all the organisms that
feed at a particular link in a food chain.
A diagram that link organisms together
by who eats whom is called a food
chain.
A grazing food chain:
Leaves → caterpillars → tree birds → hawks
A detrital food chain:
Dead organic matter → soil microbes → worms
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Food chain
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Ecological Pyramids
The shortness of food chains can be
attributed to the loss of energy between
trophic levels.
Generally, only about 10% of the energy
in one trophic level is available to the
next trophic level.
This relationship explains why so few
carnivores can be supported in a food
web.
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The flow of energy with large losses
between successive trophic levels can
be depicted as an ecological pyramid
that shows trophic levels stacked one on
the other like building blocks.
Usually a pyramid shows that biomass
and energy content decrease from one
trophic level to the next, but an inverted
pyramid occurs where the algae grow
rapidly and are consumed by long-lived
aquatic animals.
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Ecological pyramid
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Global Biogeochemical Cycles
All organisms require a variety of organic
and inorganic nutrients.
Since pathways by which chemicals cycle
through ecosystems involve both biotic
and abiotic components, they are known
as biogeochemical cycles.
Biogeochemical cycles often contain
reservoirs, such as fossil fuels,
sediments, and rocks that contain
elements available on a limited basis to
living things.
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Exchange pools are components of
ecosystems like the atmosphere, soil,
and water—which are ready sources of
nutrients for the biotic community that
uses the chemicals.
Nutrients cycle among the members of
the biotic component of an ecosystem
and may never enter an exchange pool.
Nutrients flow between terrestrial and
aquatic ecosystems.
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Model for chemical cycling
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The Water Cycle
In the water, or hydrologic cycle, the
sun’s rays cause fresh water to
evaporate from the oceans, leaving the
salts behind.
Vaporized fresh water rises into the
atmosphere, cools, and falls as rain
over oceans and land.
Precipitation, as rain and snow, over land
results in bodies of fresh water plus
groundwater, including aquifers.
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Water is held in lakes, ponds, streams,
and groundwater.
Evaporation from terrestrial ecosystems
includes transpiration from plants.
Eventually all water returns to the
oceans.
Groundwater “mining” in the arid West
and southern Florida is removing water
faster than underground sources can
be recharged.
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The water cycle
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The Carbon Cycle
In the carbon cycle, a gaseous cycle,
organisms exchange carbon dioxide with
the atmosphere.
Shells in ocean sediments, organic
compounds in living and dead
organisms, and fossil fuels are all
reservoirs for carbon.
Fossil fuels were formed during the
Carboniferous period, 286 to 360 million
years ago.
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The carbon cycle
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Carbon Dioxide and Global
Warming
The transfer rate , the amount of a nutrient
that moves from one compartment of the
environment to another, can be altered by
human activities, allowing more carbon
dioxide to be added to the atmosphere.
Atmospheric carbon dioxide has risen from
280 ppm to 350 ppm due to burning of
fossil fuels and forests.
Besides CO2, nitrous oxide and methane
are also greenhouse gases.
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Similar to the panes of a greenhouse,
these gases allow the sun’s rays to pass
through but hinder the escape of
infrared (heat) wavelengths.
Buildup of more of these “greenhouse
gases” could lead to more global
warming.
The effects of global warming could
include a rise in sea level, affecting
coastal cities, and a change in global
climate patterns with disastrous effects.
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Earth’s radiation balances
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The Nitrogen Cycle
Nitrogen makes up 78% of the atmosphere
but plants are unable to make use of this
nitrogen gas and need a supply of
ammonium or nitrate.
The nitrogen cycle, a gaseous cycle, is
dependent upon a number of bacteria.
During nitrogen fixation, nitrogen-fixing
bacteria living in nodules on the roots of
legumes convert atmospheric nitrogen to
nitrogen-containing organic compounds
available to a host plant.
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Cyanobacteria in aquatic ecosystems and
free-living bacteria in the soil also fix
nitrogen gas.
Bacteria in soil carry out nitrification when
they convert ammonium to nitrate in a
two-step process: first, nitrite-producing
bacteria convert ammonium to nitrite and
then nitrate-producing bacteria convert
nitrite to nitrate.
During denitrification, denitrifying bacteria
in soil convert nitrate back to nitrogen
gas but this does not quite balance
nitrogen fixation.
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The nitrogen cycle
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Nitrogen and Air Pollution
Human activities convert atmospheric
nitrogen to fertilizer which when
broken down by soil bacteria adds
nitrogen oxides to the atmosphere at
three times the normal rate.
Humans also burn fossil fuels which put
nitrogen oxides (NOx) and sulfur
dioxide (SO2) in the atmosphere.
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Nitrogen oxides and sulfur dioxide react
with water vapor to form acids that
contribute to acid deposition.
Acid deposition is killing lakes and
forests and also corrodes marble,
metal, and stonework.
Nitrogen oxides and hydrocarbons (HC)
react to form photochemical smog,
which contains ozone and PAN
(peroxyacetylnitrate), oxidants harmful
to animal and plant life.
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Acid deposition
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A thermal inversion, where these
pollutants are trapped under warm,
stagnant air concentrates pollutants to
dangerous levels.
Nitrous oxide is not only a greenhouse
gas, but contributes to the breakdown
of the ozone shield that protects
surface life from harmful levels of solar
radiation.
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Thermal inversion
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The Phosphorus Cycle
The phosphorus cycle is a sedimentary
cycle.
Only limited quantities are made available
to plants by the weathering of
sedimentary rocks; phosphorus is a
limiting inorganic nutrient.
The biotic community recycles phosphorus
back to the producers, temporarily
incorporating it into ATP, nucleotides,
teeth, bone and shells, and then returning
it to the ecosystem via decomposition.
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The phosphorus cycle
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Phosphorus and Water Pollution
Phosphates are mined for fertilizer
production; when phosphates and
nitrates enter lakes and ponds,
eutrophication occurs.
Many kinds of wastes enter rivers which
flow to the oceans; oceans are now
degraded from added pollutants.
If pollutants are not decomposed, they
may increase in concentration as they
pass up the food chain, a process called
biological magnification.
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Chapter Summary
An ecosystem includes autotrophs that
make their own food and heterotrophs
that take in preformed food.
Solar energy enters biotic communities
via photosynthesis, and as organic
molecule pass from one organism to
another, heat is returned to the
atmosphere.
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Chemicals cycle within and between
ecosystems in global biogeochemical
cycles.
Biogeochemical cycles are gaseous
(carbon cycle, nitrogen cycle) or
sedimentary (phosphorus cycle).
The addition of carbon dioxide (and other
gases) to the atmosphere is associated
with global warming.
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The production of fertilizers from
nitrogen gas is associated with acid
deposition, photochemical smog, and
temperature inversions.
Fertilizer also contains mined phosphate;
fertilizer runoff is associated with water
pollution.
Certain pollutants undergo biological
magnification as they pass through the
food chain.
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