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Secrets of the Crocodile Caves

Classroom Activity

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Objective
To learn about a small segment of the complex food web of a region in Madagascar.

Materials for each group
  • copy of the "Home Sweet Home" student handout (PDF or HTML)
  • several sheets of unlined paper
  • ruler

Procedure
  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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?

  6. 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.

Activity Answer

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.

Sample Food Web
Links and Books

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.


Standards

The "Home Sweet Home" activity aligns with the following National Science Education Standards.

Grades 5-8

Life Science

Science Standard C:
Life Science

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.


Grades 9-12

Life Science

Science Standard C:
Life Science

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.

Teacher's Guide
Secrets of the Crocodile Caves
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