Secrets of the Crocodile Caves
To learn about a small segment of the complex food web of a region in Madagascar.
- copy of the "Home Sweet Home" student handout
- several sheets of unlined paper
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.
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.
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.
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
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?
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.
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
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.
NOVA Web Site—Secrets of the Crocodile Caves
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
Highlights the biodiversity of Madagascar, including a section on the dry
Sights & Sounds—Madagascar Dry Forests
Shows photos and video clips of some of Madagascar's rare animals, such as
fossas and crowned lemurs.
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.
The Eighth Continent: Life, Death, and Discovery in the Lost World of
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
Science Standard C:
Populations and ecosystems:
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.
Science Standard C:
The Interdependence of Organisms:
Energy flows through ecosystems in one direction, from photosynthetic organisms
to herbivores to carnivores and decomposers.
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.