Food Chains, Food Webs, and
Energy Pyramids
Chapter 13, Section 13.4
This is called an
energy pyramid. It
shows how energy
is lost moving from
the producers to
each subsequent,
higher, trophic level.
Objectives
• To describe the structure of a food chain.
• To explain how food chains and trophic levels
are related.
• To analyze feeding relationships in a food web.
• To compare and contrast our place in the food
chain with that of our ancestors.
Vocabulary (all between pp. 408-411)
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Food chain
Herbivore
Carnivore
Omnivore
Detritivore
Decomposer
Specialist
Generalist
Tropic level
Food web
Starter
• I want you to think about and describe a
typical meal.
• What do you get from these foods?
• How does energy and matter come to be in
these foods?
– Draw a food chain or food web showing the
relationship of you to your food.
Food Chains and Food Webs (Main
Ideas)
• They are models for determining the
relationships among species.
– They can become very complex because they can
deal with hundreds, in certain cases thousands, of
species.
• We talked about energy in ecosystems in Unit
13.3, now we are going to be studying how
that energy is transferred from organism to
organism in an ecosystem.
Energy Loss with Increase in Trophic
Level
Food Chain – A Simple Model
• A food chain is a model of energy flow in an
ecosystem.
– It is a sequence that links species by their feeding
relationships.
– A food chain is a more simple model than a food
web.
– It only follows the connection between on
producer and a single chain of consumers within
an ecosystem.
Food Chain
A Prairie Food Chain: Little Bluestem Prairie Grass
(Producer) Eaten by Black Tailed Prairie Dog (Primary
Consumer) Eaten by Coyote (Secondary Consumer)
Food Chain
• Take a moment to think about a food chain.
• Draw it in your notebook.
• Share with class.
Types of Consumers
• Herbivores – organisms that eat only plants
(like our prairie dogs, Canada goose, goats,
huemul, pandas).
Types of Consumers
• Carnivores – organisms that eat only animals.
– Ex. Jaguar, Philippine Eagle, and army ant.
Army Ants
• https://www.youtube.com/watch?v=UozWJTu
hbMQ
• This is a You Tube video of army ants. It
discusses their mode of predation.
• Where do army ants fit in a tropical food
chain?
Types of Consumers
• Omnivores – organisms that eat both plants
and animals (Ex. Crows, coyotes, grizzly bears,
Kangaroo rat, New Guinea singing dog).
Types of Consumers
• Detritivores – organisms that eat detritus, or
dead organic matter (millipede, buying beetle,
woodlouse, etc.)
Types of Consumers
• Decomposers – detritivores that break down
organic matter into simpler compounds.
Fungi are the classic example of decomposers.
• They are vital to the stability of an ecosystem
– returning vital nutrients back into the
environment.
Specialists
• Specialists are consumers that primarily feed
on one specific organism or a very small
number of organisms.
• Examples of specialists: giant pandas, Florida
Due to their highly
snail kite, koala.
specialized diets,
Florida snail kite eats primarily
apple snails.
Koalas eat only eucalyptus
leaves.
specialists are often
endangered. If the
population of the
organism the specialist
depends upon for its food
declines, the population of
the specialist also declines.
Generalists
• Most species do not rely on a single source of
food.
• Generalists are consumers that have varied
diets. Examples include raccoons, opossum,
coyotes, and crows.
• Generalists are typically very adaptable.
Trophic Levels
• Levels of nourishment in a food chain.
• The basic food chain is producer-herbivorecarnivore.
– Carnivores is at the highest trophic level.
– Herbivores are at the second trophic level.
– Producers are the base – first trophic level.
20
Energy Flows Up the Food Chain
• Energy flows from lowest trophic level to
highest.
• Primary consumers are herbivores – they are
the first consumer above the producer base
trophic level.
• Secondary consumers are carnivores that eat
the herbivores.
• Tertiary consumers are carnivores that eat
secondary consumers.
Loss of Energy Moving up Food Chain
As you move up a food chain
(and a food web – see later
slides) energy is lost at each
step. We can show the loss of
energy conveniently in an
energy pyramid (on the left).
This loss of energy is one reason
there are more primary
consumers (herbivores) than
secondary consumers
(carnivores) – and so-on-and-soforth.
Predators are rare compared to
their prey.
Loss of Energy Moving up Food Chain
• Tallgrass prairie energy pyramid. As you can
see, the loss of energy between trophic levels
is severe.
This
shows a
real
food
chain.
Losses would be, for example, from little bluestem
grass to prairie dogs, and prairie dogs to coyotes.
Where the Omnivore Fits-in
• Omnivores, such as black bears and humans,
eat both plants and animals.
• Therefore, they may be listed at different
trophic levels in different food chains.
– Ex. if you eat your vegies (as you should), you are
a primary consumer.
Quick Test of Understanding
• True or False:
• Organisms higher up in a food chain eat
everything that is lower.
• That is false
• Populations higher in a food chain increase in
number because they deplete those lower in
the chain.
• That too is false (if they do, it is a brief
imbalance).
Quick Test of Understanding
• The top of the food chain has the most energy
because it accumulates up the chain.
• That, once again, is false.
Coral Reef Food Web
Coral reefs
are called
the tropical
rainforests
of the
ocean. They
are
extremely
rich in
biodiversity.
Food Webs
• A food web is a model that shows the complex
network of feeding relationships and the flow
of energy within and sometimes beyond an
ecosystem (see preceding slide).
• Food webs are more complex models of
ecosystems than food chains.
– Many organisms, especially generalists, play
multiple roles in an ecosystem and thus are
connected to many different levels (ex. a raccoon).
Food Webs
• The stability of a food web depends on the
presence of producers (form the base of the
web).
• In marine ecosystems, such as the coral reef,
algae and phytoplankton are two of the
producers that play an important role.
• 90% loss of energy between trophic levels
(algae and fish that eat algae, and reef sharks
and the algae eating fish).
Review Questions
• Q: Why are food chains especially useful for
describing the relationship of specialists?
• A: Specialists have specific diets that include
only one type of organism, which produces a
simple food chain (Examples: snail kite and
apple snail, blue whale and krill).
Review Questions
• Q: What happens to energy as it flows through
a food web?
• A: Some energy is stored in the organism but
much energy is dissipated into the
environment.
Review Questions
• Q: Only a small percentage of all consumers
are specialists. What danger does a specialist
face that a generalist does not?
• A: If a specialist’s food source becomes scarce
or disappears, the population may go extinct.
A generalist can always shift to another food.
Review Questions
• Q: How might the stability of an ecosystem be
affected if all of the decomposers were
suddenly removed?
• A: Without decomposers, vital nutrients
would not be returned to the ecosystem. The
ecosystem would be unstable.
Review Questions
• Q: How might an oil spill in the ocean affect an
aquatic food web? What might happen to the
food web on land located near the spill? Explain
your answers.
• A: The entire food web would be affected. Oily
water would kill off phytoplankton which feeds
small fish. The number of small fish would be
reduced affecting larger fish (secondary
consumers), which would affect the tertiary (third
level) consumers. As oil seeps on shore, plants
and animals living along the shore would be
negatively affected – oil is toxic.
Antarctic Food Web
More Review Questions (Not to Be
Turned In)
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An organism that eats only plants
An organism that eats only other animals
An organism that eats both plants and animals
An organism that eats dead organic matter
An organism that breaks down organic matter into simpler
compounds (like minerals)
What is the first consumer above the producer level called?
What is a carnivore that eats herbivores called (what is its
trophic level)?
What is a carnivore who eats other carnivores called?
What are the levels of nourishment in a food chain called?
More Review Questions (Not to Be
Turned In)
• How is a food web different from a food
chain?
• What happens to energy at each link in a food
web?
• What type of organism provides the base of a
food web?
• What is the difference between a specialist
and a generalist?
• What does an energy pyramid show?