Download Ecosystems

18.3 Energy Transfer

Photosynthetic organisms convert solar energy into
energy-rich organic compounds.

They then use the organic compounds as fuel for
their metabolic processes and some is stored.

The energy moves through the ecosystem as one
organism consumes another for food.

The flow of energy is one way:
Sun
photosynthetic organisms
other organisms

Usually a photosynthetic organism
 6CO2 + 6H2O

C6H12O6 + 6O2
Also referred to as producers because they make
food that is used by the entire community.
• Example: Algae which are phytoplankton and plants.

Some autotrophs are chemosynthetic - use inorganic
compounds as an energy source (sulfur compounds,
ammonia)
• Chemosynthetic producers can be found in deep sea
communities and other extreme environments.



Biomass - the organic material added by producers
in an ecosystem.
Gross Primary Productivity (GPP) =
Total amount of light energy converted to chemical
energy in organic material
Net Primary Productivity (NPP) =
GPP minus the energy used by organisms for cellular
respiration (GPP – CR)
 C6H12O6 + 6O2
6CO2 + 6H20 + energy
 An
organism that cannot make its own food.
 Obtains energy and nutrients by consuming
other organisms.
 Also referred to as the consumers of an
ecosystem.
 Herbivores, Carnivores and Omnivores or….
• Lions and Tigers and Bears, oh my!
 Detritivores-
obtain energy from dead and
decaying organisms.
• Scavengers - vultures and hyena
• Decomposers - bacteria and fungi
 The
pathway for the transfer of energy within
an ecosystem from one trophic level to the
next.
• Trophic level - the position in the sequence of
energy transfers.
 Each
organism provides food for the next
higher level.
 Meadow
Ecosystem
• Sunflower (producer)
• Caterpillar eats sunflower leaves (consumer)
• Blackbird eats the caterpillar (consumer)
• Fox eats the blackbird (consumer)
• Bacteria and fungi consume the remains of any dead
organisms (decomposers)
 Only
some of the energy and matter is
transferred each time one organism consumes
another.
 At every step in the food chain, part of the
energy is lost to metabolism and as heat to the
environment.
 Because of this energy loss, food chains
generally support no more than 4 links.



Each step in the transfer of energy and
matter in an ecosystem.
1. Producers: the autotrophs, the source of
organic molecules.
2. Primary consumers: feed directly on
producers. Herbivores are primary
consumers that eat plants.


3. Secondary consumers: feed directly on
primary consumers. Carnivores only eat
meat.
4. Tertiary consumers: feed on secondary
consumers.
Transfer of Energy
Decomposer
Tertiary Consumer
Secondary Consumer
Primary Consumer
Producer
Food Web
Most
organisms in
an ecosystem
eat more than
one kind of
food.

 Omnivore:
eat both producers and other
consumers.
• May be primary, secondary or tertiary because they
feed on all levels
 Scavenger:
a consumer that feeds on the
tissues of dead animals.
• vultures, crows, ants, etc.
 Decomposers:
bacteria or fungi that feed on
wastes and dead organic matter from all
trophic levels.
• Break down complex organic compounds into
simpler nutrients.
• Nutrients are returned to soil or water where
producers reuse them.
• Recycling nutrients is critically to all trophic levels.
 The
transfer of energy from one trophic level to
the next is not very efficient.
 Only a fraction of the energy (about 10-20%)
moves from one trophic level to the next.
• Known as the
10% Rule
 1.
Much of the energy consumed is used for
metabolism and life processes.
 2. Many of the organisms are not consumed by
the organisms at the next trophic level.
 3. Some of the energy at each trophic level is in
materials that consumers at the next level are
not likely to eat.
• Ex: wood, bones, teeth, beaks, and shells
 Shows
the relationships between trophic levels
in an ecosystem
• Producers and Consumers
• Energy Flow
• Biomass - the mass
of organic material
in a trophic level
• Numbers
 In
most ecological pyramids, fewer organisms
occupy each higher trophic level
• Meadow covered by grasses and plants
• Meadow has many primary consumers such as mice
and insects
• Less secondary consumers such as snakes, robins
etc.
• Even less amount of tertiary consumers such as
hawks and tigers
 Energy
Flow
 The
number of organisms at each trophic level
is proportional to the amount of biomass and
energy available at the level below it.
 Resources at lowest level determine how much
life the environment can support.
• What is the primary resource?
 The
more biomass and energy the producers
supply, the more the environment can handle.
 The
pesticide DDT was used to kill insects that
damaged crops.
 Went into the soil and ran off into rivers and
lakes.
 Contaminated planktonic organisms.
 Transferred to fish and then to bigger fish in
even higher concentrations.
• biological magnification: buildup of a pollutant in
organisms at higher trophic levels of food chains.
 Bald
eagles ate the large contaminated fish.



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
DDT was now in bird tissues at levels ten million times
the original concentration of DDT in the water.
Interfered with the formation of eggs shells making
them soft.
Eggs broke easily and embryos inside did not survive.
Eagle population declined.
DDT banned in the United States.