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Secrets of the Crocodile Caves
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Classroom Activity
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Objective
To learn about a small segment of the complex food web of a region
in Madagascar.
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copy of the "Home Sweet Home" student handout (PDF
or
HTML)
- several sheets of unlined paper
- ruler
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Organize students into groups of three so that one member of
each group has notes on the different categories outlined in the
Before Watching activity #3. Provide copies of the student
handout and other materials to each group.
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Discuss with students the concept of a food web. They are
probably familiar with a simple food chain (e.g., grain is eaten
by mice that are eaten by an owl). A food web is a more complex
model of feeding relationships that includes many interconnected
food chains.
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After watching, have students in each group identify all the
plants and animals on the student handout and draw arrows from
each plant or animal to the animal that eats it. Then, using
their program notes and student handout, have students draw a
food web for the plants and animals of northern Madagascar. Note
to students that these plants and animals are only a small part
of the food web in this region of Madagascar. Ask students to
draw arrows from an animal or plant to the animal that eats it
to illustrate how energy flows through the food web.
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Ask students to choose one food chain from their food web to
draw an energy pyramid. An energy pyramid shows how energy flows
through the food chain.
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To conclude, hold a class discussion about the balance of the
food web. What might happen if one organism were taken out of
the web? What if an organism, such as another species of lemur,
were added?
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As an extension, have students investigate what other plants and
animals live on Madagascar and brainstorm how those plants and
animals might fit into the food web students created.
As you review completed food webs with students, remind them that
the animals and plants they used for their food web are just a small
segment of the living organisms on Madagascar. The real food web is
far more complex. This web below shows some of the interactions
among plants and animals.
Some of the foods crowned lemurs eat are figs, flowers, and leaves.
(They also eat tamarind pods, tree fruits, cicadas, screw plants,
and other items not shown in this film.) Two of the crowned lemur's
predators are crocodiles and fossas. The crowned lemur's competitors
include Sandford's lemurs and ring-tailed mongooses.
If the fig trees were struck by disease, the population of crowned
lemurs might decrease. Predator populations might also decrease.
Since figs are not only a staple for crowned lemurs, but also for
their competitors, the populations of many species dependent on figs
would decrease. Their predators would grow hungry and possibly
starve.
The animals that crocodiles eat that are shown on this program
include crowned lemurs, domesticated zebu, and blind fish and
shrimp. The population of crocodiles is affected by the availability
of their prey.
Web Sites
NOVA Web Site—Secrets of the Crocodile Caves
www.pbs.org/nova/croccaves/
In this companion Web site for the NOVA program, view panoramas of
Ankanara, learn about the legends of Madagascar, find a who's who of
crocodile species, and explore the anatomy of a crocodile.
Madagascar: Biodiversity and Conservation
ridgwaydb.mobot.org/mobot/madagascar/
Highlights the biodiversity of Madagascar, including a section on
the dry tropical forest.
Sights & Sounds—Madagascar Dry Forests
www.nationalgeographic.com/wildworld/madagascar/
Shows photos and video clips of some of Madagascar's rare animals,
such as fossas and crowned lemurs.
Books
Garbut, Nick.
Mammals of Madagascar.
New Haven: Yale University Press, 1999.
Provides an overview of Madagascar's diverse group of 117 mammal
species, more than 100 of which are endemic to the island.
Tyson, Peter.
The Eighth Continent: Life, Death, and Discovery in the Lost
World of Madagascar.
New York: William Morrow, 2000.
Describes Madagascar through the eyes of four scientific
experts—a herpetologist, a paleoecologist, an archeologist,
and a primatologist—as they explore the world's fourth-largest
island.
The "Home Sweet Home" activity aligns with the following National
Science Education Standards.
Grades 5-8
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Science Standard C:
Life Science
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Populations and ecosystems:
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The number of organisms an ecosystem can support depends on the
resources available and abiotic factors, such as quantity of
light and water, range of temperatures, and soil composition.
Given adequate biotic and abiotic resources and no disease or
predators, populations (including humans) increase at rapid
rates. Lack of resources and other factors, such as predation
and climate, limit the growth of populations in specific niches
in the ecosystem.
Grades 9-12
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Science Standard C:
Life Science
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The Interdependence of Organisms:
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Energy flows through ecosystems in one direction, from
photosynthetic organisms to herbivores to carnivores and
decomposers.
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Living organisms have the capacity to produce populations of
infinite size, but environments and resources are finite. This
fundamental tension has profound effects on the interactions
between organisms.
Classroom Activity Author
Dwight Sieggreen has been teaching middle school science for 35
years in Northville, Michigan. He currently serves as president of
the National Association of Presidential Awardees for Excellence in
Science Teaching.
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