Food Chains, Food Webs, and Energy Pyramids Chapter 13, Section
13.4
Slide 2
This is called an energy pyramid. It shows how energy is lost
moving from the producers to each subsequent, higher, trophic
level.
Slide 3
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.
Slide 4
Vocabulary (all between pp. 408-411) Food chain Herbivore
Carnivore Omnivore Detritivore Decomposer Specialist Generalist
Tropic level Food web
Slide 5
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.
Slide 6
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.
Slide 7
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.
Slide 8
Food Chain A Prairie Food Chain: Little Bluestem Prairie Grass
(Producer) Eaten by Black Tailed Prairie Dog (Primary Consumer)
Eaten by Coyote (Secondary Consumer)
Slide 9
Food Chain Take a moment to think about a food chain. Draw it
in your notebook. Share with class.
Slide 10
Types of Consumers Herbivores organisms that eat only plants
(like our prairie dogs, Canada goose, goats, huemul, pandas).
Slide 11
Types of Consumers Carnivores organisms that eat only animals.
Ex. Jaguar, Philippine Eagle, and army ant.
Slide 12
Army Ants https://www.youtube.com/watch?v=UozWJTu hbMQ
https://www.youtube.com/watch?v=UozWJTu hbMQ This is a You Tube
video of army ants. It discusses their mode of predation.
Slide 13
Types of Consumers Omnivores organisms that eat both plants and
animals (Ex. Crows, coyotes, grizzly bears, Kangaroo rat, New
Guinea singing dog).
Slide 14
Types of Consumers Detritivores organisms that eat detritus, or
dead organic matter (millipede, buying beetle, woodlouse,
etc.)
Slide 15
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.
Slide 16
Specialists Specialists are consumers that primarily feed on
one specific organism or a very small number of organisms. Examples
of specialists: giant pandas, Florida snail kite, koala. Florida
snail kite eats primarily apple snails. Koalas eat only eucalyptus
leaves. Due to their highly specialized diets, 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.
Slide 17
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.
Slide 18
Trophic Levels Levels of nourishment in a food chain. The basic
food chain is producer-herbivore- carnivore. Carnivores is at the
highest trophic level. Herbivores are at the second trophic level.
Producers are the base first trophic level.
Slide 19
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.
Slide 20
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-so- forth. Predators are rare compared to their
prey.
Slide 21
Loss of Energy Moving up Food Chain Tallgrass prairie energy
pyramid. As you can see, the loss of energy between trophic levels
is severe. Losses would be, for example, from little bluestem grass
to prairie dogs, and prairie dogs to coyotes.
Slide 22
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.
Slide 23
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).
Slide 24
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.
Slide 25
Coral Reef Food Web Coral reefs are called the tropical
rainforests of the ocean. They are extremely rich in
biodiversity.
Slide 26
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).
Slide 27
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. Also severe loss of energy between
trophic levels (algae and fish that eat algae, and reef sharks and
the algae eating fish).
Slide 28
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).
Slide 29
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.
Slide 30
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 specialists food source becomes scarce
or disappears, the population may go extinct. A generalist can
always shift to another food.
Slide 31
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.
Slide 32
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.
Slide 33
Slide 34
Antarctic Food Web
Slide 35
More Review Questions (Not to Be Turned In) 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?
Slide 36
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?
