Ecology
2c- Energy Flow in Ecosystems
Ecosystem Requirements
• #1 - Continuous supply of energy
• #2 – A flow of energy from one population to
another
Obtaining Energy
• Autotrophs - use energy from
the sun or energy stored in
chemical compounds to produce
energy (aka producers)
• Heterotrophs – must consume
their energy (aka consumers)
–
–
–
–
Herbivores
Carnivores
Omnivores
Detritivore (AKA decomposers)
Herbivores
• Eat plants (autotrophs)
Carnivores
• Eat other heterotrophs
– Predators – kill their own food
– Scavengers – eat animals that are already
dead/weak/sick
Omnivores
• Eat both autotrophs and heterotrophs (plants
and animals)
Detritivore
• AKA decomposers – decompose organic
matter and return nutrients to soil, water, and
air
– Ex. fungus, bacteria
– Teded: Dead Stuff
Energy Flow
Food Chain• a single pathway of feeding
relationships among organisms in an
ecosystem that results in energy
transfer
Energy Flow
• FOOD WEB
– A diagram of the
feeding relationships
among all of the
organisms in an
ecosystem
– Many food chains
interlinked
Food Web
Energy Pyramid
• The energy pyramid is made of several trophic levels
• A Trophic Level (or feeding level) is a group of
organisms whose feeding source is the same number
of steps from the Sun.
– Primary Producers (Autotrophs) are the First Trophic
Level.
– Primary Consumers (Herbivores) are the Second Trophic
Level.
– Secondary and Tertiary Consumers
(Carnivores/Omnivores/Predators) are the Third and
Fourth Trophic Levels.
– Most Animals feed at more
than one Trophic Level.
Trophic Levels
• Energy is Lost or Used as it flows through the Trophic Levels
of an Ecosystem.
• Producers absorb energy from the Sun
– Only about ½ of the energy captured from the Sun becomes part
of the plants body.
– Other ½ is used for living and growing or lost as heat.
• At each Trophic Level, the energy stored in an organism is
about 1/10 that of the level below it (10%).
Trophic Levels
• Because energy diminishes at each successive
Trophic Level, most terrestrial ecosystems
have only 3-4 trophic levels.
– Marine ecosystems often have more
• Organisms at higher Trophic Levels (large
carnivores) tend to be fewer in number than
those at lower Trophic Levels (producers.)
Number and Biomass Pyramids
• The number of
organisms at
each trophic
level decreases
as you step up
the pyramid.
• Biomass (living
organic matter)
is reduced at
each trophic
level as well
Bioaccumulation/Biomagnification
• Bioaccumulation begins at the first level of a food chain
where there is an increase in the concentration of a
pollutant from the environment to the 1st organisms in
the chain.
• Biomagnification occurs when the concentration of a
pollutant increases from one link in the food chain to
another
– Because the amount of energy required gets higher at each
level, those organisms have to consume more and thus can
accumulate higher levels of the contaminants in their bodies
– Will result in the top predators containing the highest
concentration levels
Bioaccumulation/Biomagnification
• A pesticide that you put on your yard is consumed by the
grasshoppers that live there. The partridge eats
10 grasshoppers. The hawk eats 3 partridges.
– If the grasshopper consumed 1 mg of the pesticide,
the partridge ingested 10mg, and the hawk
consumed 30mg.