18-3 Energy Transfer
Producers and Consumers
Objectives
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•
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Summarize the role of producers
Identify kinds of consumers
Explain the role of decomposers
Compare food chains and food
webs
• Explain why there are only a few
trophic levels in an ecosystem
Producers
• Autotrophs: make their own
energy/food
–As producers they make energy
that other organisms can use
• Photosynthesis: Energy from light
• Chemosynthesis: Energy from
chemicals
Deep sea
ecosystems survive
on chemosynthesis
Riftia tubeworms, mussels, and scavenging
crabs found at the hydrothermal vent site
Measuring productivity
• Gross primary productivity: Rate that
producers catch sun’s energy
– Producers store energy in sugars
• Biomass: All the organic material
• Net primary productivity: how much
biomass piles up
– GPP minus rate of respiration
– Kcal/m2/year
– g/m2/year
– Where do you think there is high Net PP
– What about aquatic environments?
Only 5 % of
the Earth’s
surface is
jungles that
account for
30% of its
NPP
Weather
accounts for
a lot of NPP.
Estuaries
also have
high levels
of NPP
because
there is so
much light
and
nutrients
Consumers
• Heterotrophs: get energy from outside of
themselves
– Eat or consume something else
Vore = Eat
• Herbivore: eat producers (plants or herbs)
• Carnivore: eat other consumers
– Carn = flesh
• Omnivore: eat everything
– Omin = all
– Most things are really at least a little bit of an
omnivore, even lions
• Detrivore: eat waste
– Detri = garbage
– Decomposers important
Others
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•
•
•
Insectivore
Bovivore
Planktavore
Cannibal: happens in nature
– Black widows, Mantis : eats the father
– Mice will kill the babies if the nest is
repeatedly threatened
– Many father’s kill the young
– Why do this?
Energy flow
• When you eat
something energy
moves into you
• Trophic level: where
do you fit in the food
chain? Who eats you
and who do you eat?
Food Webs
• There are many trophic relationships
• Food webs show the many connections
between eater and eaten
Energy transfer
• How much does each trophic level store?
– Only 10% of the energy makes it up to the
next level
• Why is so much energy lost?
– Some prey escape
– You can’t eat everything when you do catch
prey
– Entropy: energy is always lost
• There are only a few trophic levels
because energy runs out
Biological
magnification
• toxins become
more
concentrated
with each link in
a food chain.
• top-level
carnivores are
usually most
severely
affected by toxic
compounds
How do
producers and
consumers
obtain energy?
• Producers: from light or
chemicals
• Consumers: from eating
something else
Name four types of consumers
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•
•
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Herbivore
Carnivore
Detrivore
Insectivore
What important role do decomposers
play in an ecosystem?
• Decomposers remove
wastes preventing
them from building
up.
How does a food chain
differ from a food web?
• Food chains are linear
(straight)
• Food webs are spatial, and
show more connections
Give two reasons for the low rate of
energy transfer within ecosystems
• Some prey
escape
• You can’t eat
everything
when you do
catch prey
• Entropy: energy
is always lost
Explain why food chains usually do
not exceed three to four levels
• There is a low rate of
energy transfer
• Very little energy gets
transferred up
• Soon there isn’t enough
energy to sustain life
pietà (pl. same; Italian for compassion)
is an artwork depicting the Virgin Mary
cradling the dead body of Christ. As
such, it is a particular form of the
devotional theme of Our Lady of
Sorrows.
• American Pieta
What happens to an ecosystem if all the
plants die? What happens if all the
decomposers die?
• If the plants die then the herbivores die, and
then the carnivores die.
• If decomposers die then waste will pile up
eventually poisoning the ecosystem
What is unreasonable about an
ecosystem with 7 levels?
• There are to many levels because There is
a low rate of energy transfer
• Very little energy gets transferred up
• Soon there isn’t enough energy to sustain
life
Explain why there are more
herbivores than carnivores
• Herbivores get energy from the largest source of
biomass: plants
• Carnivores can’t get as much energy by eating
other consumers
• This Biology
Lecture
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