Once the realm of the ancient Incan Empire, this place of myth and legend also has a rich, intriguing natural history going back to the Jurassic period, marked by an event of monumental portion—the formation of the Central American land bridge 3 million years ago. The creatures of the Andes set this land apart from all other places on earth. The Andes are home to the zorro, a “false fox” with adaptations that make it a successful inhabitant of the Andes. The flamingo, too, has developed utterly unique and specialized adaptations in order to thrive in an environment that doesn’t even seem livable—a salt pan.

Only a mountain range of extremes could harbor such a rich and diverse variety of life forms. Here you will find some of the highest, saltiest, wettest and driest terrains on the planet. Penguins, opossums, hummingbirds, llamas, pumas, foxes, condors, spectacled bears and many more have all managed to carve out an existence somewhere in one of the many worlds that we call the Andes.

To order a copy of Andes: The Dragon’s Back, please visit the NATURE Shop.

Online content for Andes: The Dragon’s Back was originally posted February 2007.

This program premiered January 12, 2003.

From its headwaters in Minnesota to the mouth of the Ohio River at Cairo, Illinois, the Upper Mississippi River is flanked by diverse terrain sheltering a wide variety of wildlife.  Nearby prairies make perfect havens for rabbits and mice.  Possum, skunks, red fox, deer, woodchucks and wild turkeys scurry amid the trees in the hardwood forests that cover the high bluffs and hillsides overlooking the river.  The waters are filled with fish and overhead, ducks and geese traverse the skies while bald eagles thrive in the upper branches of cottonwoods.

That’s right. Bald eagles have returned to the Upper Mississippi Valley. In the 1960s, ecologist and writer Rachel Carson, who had publicized the claim that DDT was killing bald eagles and other birds, organized a bald eagle count along the entire length of the river that turned up only 59 individuals. Now, up to 2,500 bald eagles spend the winter along the Mississippi, with a smaller — though increasing — number staying year-round to nest.

While most adult eagles that live in southern states will remain in their nesting area through the year, bald eagles that spend the mating season in colder regions must migrate to survive.  In October, juvenile eagles in Canada and the northern reaches of Minnesota and Wisconsin are the first to leave.  Even those migrating for the first time find their way by instinct. By mid-November, adult eagles that nest in these colder areas will also start to head south as their nesting lakes begin to freeze. 

It’s not the cold itself that poses the greatest danger when winter sets in. These birds are actually quite rugged. Instead, it’s the need for a stable food source that drives the migrations. Living in the cold requires more energy, and thus more food.  In winter, an eagle must consume 6 to 11 percent of its body weight each day.  Their primary food source is fish, supplemented by ducks, coots, carrion and small mammals. When ice begins to form their access to food is cut off, and eagles move to where the water is still open.

The migrating eagles make their way by riding thermals, currents of warmer air that rise from the bluffs and hillsides lining the river corridor. When conditions are right, bald eagles can travel up to 270 miles in a day.  But, when tailwinds dissipate or thermals are scarce, bald eagles will linger.  In time, many will find their way to the Upper Mississippi River Valley, where stretches of the river are fed by tributary waters and do not freeze.

Elsewhere on the river, human intervention has unintentionally created a favorable environment for raptors. At one time, the entire Upper Mississippi flowed freely from its source all the way to where it joins the Ohio River. In the 1930s, however, the US Army Corps of Engineers began constructing what is now a system of 29 locks and dams on the Mississippi.  Where surging rapids and waterfalls once prevailed, humans created a navigable transportation route that supports both recreation and commerce.  As it turns out, these changes were not only good for cargo barges that carry petroleum, coal, and agricultural goods. They were also good for the eagles.  In winter, when bald eagles spend upwards of 90 percent of daylight hours roosting in order to conserve their energy, the fish that have been stunned or killed in the turbulent waters around dams provide an easy meal.  Elsewhere, power plants use river water for cooling, then pump the warmed water back into the river. In these places, large groups of eagles can be seen gathering around the open waters, freed from the ice, where they can take advantage of plentiful, and accessible, supplies of gizzard shad and other fish. 

Near the end of winter, as early as February, those eagles that have migrated south begin to follow the thaw back to their northern homes. Others, like the nesting pair at the Iowa hatchery in American Eagle, never migrate. They stay within several square miles of their nesting site throughout the year. During the spring and summer, all the eagles in the area become very territorial, protecting the resources that will sustain their young.  But at least with the migrating  “visitors” gone, the riches of the Upper Mississippi River Valley belong to its year-round residents.

Photo © Neil Rettig

Background:
Sharks and their biological cousins, the rays, are among the highest-profile denizens of the deep. But sharks are not the solitary killing machines that popular movies and the press might have us believe. In their marine environment, sharks coexist with numerous other species – many of whom flock to be near the sharks, rather than running from them in fear. These excerpts from the NATURE episode “The Secret World of Sharks and Rays” examine the interrelationships between sharks and other marine species. In many of these cases, the interaction between two different species mutually benefits each species. But humans, too, have become an increasingly important player in the lives of sharks – and as they are increasingly hunted for their fins, sharks are actually becoming more endangered than they are dangerous. The impact on the marine ecosystem that would result from the disappearance of sharks would be devastating, but there is still time to save these magnificent creatures, and the ecosystems that depend on their existence.

Suggested focus questions:

Clip 1: Shark and Turtle

1. How does the turtle protect itself?
2. What relationship is held between the tiger shark and the loggerhead turtle?

Clip 2: Unlikely Travel Companions

1. List three ways in which being near a shark might be beneficial to a fish.
2. What is one way that a shark might benefit from a fish (other than as prey)?
3. Classify each shark-fish relationship shown in this clip as commensalism, mutualism, or parasitism.

Clip 3: Sharks and Fishermen

1. How have sharks become trained to follow fishermen?
2. Describe how the following species pairs interact in the clip: fishermen/fish; sharks/fish; sharks/fishermen.

Clip 4: Collapse of Sharks

1. Why are shark populations in danger of collapse?
2. How has the relationship between sharks and humans changed over time?
3. What might happen if the shark fin trade continues unchecked?

Clip 5: Sharks in our Future

1. Describe the type of tourism seen in this clip.
2. What benefit do these businesses provide to: sharks? To local populations? To tourists?
3. How might these businesses help prevent the collapse of shark populations?

Downloadable QuickTime versions of the video segments:
(Note: To download a video, right-click on the video title and click “Save Link As…” or “Save Target As…”. On a Mac, press the CTRL key and simultaneously click the mouse, then save the link.)

Clip 1: “Shark and Turtle”

Clip 2: “Unlikely travel companions”

Clip 3: “Sharks and fishermen”

Clip 4: “Collapse of sharks”

Clip 5: “Sharks in our future“

GRADE LEVEL: Grades 9-12

TIME ALLOTMENT: Five 45-minute class periods

OVERVIEW: This lesson focuses on symbiosis and ecological relationships. Students will investigate the many ways that species that live in close proximity to each other might interact in an ecosystem, whether via competition or predation or through an ongoing symbiotic relationship such as mutualism, commensalism, or parasitism. Segments drawn from the NATURE episode The Secret Lives of Sharks and Rays and an online interactive featuring the malaria parasite will be used to provide specific examples of these interactions. The students will discover that all ongoing ecological relationships, even parasitic or predatory ones, have evolved over long periods of time and are integral to the maintenance of the balance and stability of an ecosystem.

The lesson then moves to a discussion of the ways that ecosystems can be thrown out of balance, often as a result of human action. A video segment showing the barbaric practices of the shark fin harvesting industry is used as a case in point of a human behavior that places a species in peril. Students will brainstorm ideas for restoring the relationship between sharks and humans to a healthy balance and will view an optimistic video segment featuring the ecotourism industry. As a culminating activity, students will select a case study for which to formulate an “Ecosystem Action Plan.” They will research an ecosystem thrown out of balance by human action and will prepare a presentation for the class describing the problem and suggesting three possible actions that could be taken to rectify the imbalance.

SUBJECT MATTER: Biology/ Living Environment

LEARNING OBJECTIVES:

• Define and describe the possible ecological relationships between species that coexist in an ecosystem
• Classify specific interspecies relationships as mutualistic, commensal, or parasitic
• Understand that ecological relationships evolved over time and are integral to maintaining the balance and stability of ecosystems
• Name factors that can throw ecosystems out of balance
• Describe human actions that have contributed to ecosystem imbalance and species decline
• Suggest remedial actions to ameliorate human-caused imbalances in ecological relationships

STANDARDS AND CURRICULUM ALIGNMENT:

National Science Education Standards

CONTENT STANDARDS C: Life Science

All students should develop understanding of:

The interdependence of organisms

• Organisms both cooperate and compete in ecosystems. The interrelationships and interdependencies of these organisms may generate ecosystems that are stable for hundreds or thousands of years.
• Human beings live within the world’s ecosystems. Increasingly, humans modify ecosystems as a result of population growth, technology, and consumption. Human destruction of habitats through direct harvesting, pollution, atmospheric changes, and other factors is threatening current global stability, and if not addressed, ecosystems will be irreversibly affected.

New York State Regents Core Curriculum Alignments

Living Environment Core Curriculum

Standard 1: Students will use mathematical analysis, scientific inquiry, and engineering design, as appropriate, to pose questions, seeks answers, and develop solutions.

Key Idea 1: The central purpose of scientific inquiry is to develop explanations of natural phenomena in a continuing and creative process.

Performance Indicator 1.1: Elaborate on basic scientific and personal explanations of natural phenomena, and develop extended visual models and mathematical formulations to represent one’s thinking.

1.1a scientific explanations are built by combining evidence that can be observed with what people already know about the world.

Performance Indicator 1.2: Hone ideas through reasoning, library research, and discussion with others, including experts.

1.2a Inquiry involves asking questions and locating, interpreting, and processing information from a variety of sources.

1.2b Inquiry involves making judgments about the reliability of the source and relevance of information.

Standard 4: Students will understand and apply scientific concepts, principles, and theories pertaining to the physical setting and living environment and recognize the historical development of ideas in science.

Key Idea 1: Living things are both similar to and different from each other and from nonliving things.

Performance Indicator 1.1: Explain how diversity of populations within ecosystems relates to the stability of ecosystems.

1.1c In all environments, organisms compete for vital resources. The linked and changing interactions of populations and the environment compose the total ecosystem.

1.1d The interdependence of organisms in an established ecosystem often results in approximate stability over hundreds and thousands of years. For example, as one population increases, it is held in check by one or more environmental factors or another species.

1.1f Every population is linked, directly or indirectly, with many others in an ecosystem. Disruptions in the numbers and types of species and environmental changes can upset ecosystem stability.

Key Idea 6: Plants and animals depend on each other and their physical environment.

Performance Indicator 6.1: Explain factors that limit growth of individuals and populations.

6.1g Relationships between organisms may be negative, neutral, or positive. Some organisms may interact with one another in several ways. They may be in a producer/consumer, predator/prey, or parasite/host relationship or one organism may cause disease in, scavenge, or decompose another.

Performance Indicator 6.3: Explain how the living and nonliving environments change over time and respond to disturbances.

6.3c A stable ecosystem can be altered, either rapidly or slowly, through the activities of organisms (including humans), or through climatic changes or natural disasters. The altered ecosystem can usually recover through gradual changes back to a point of long-term stability.

Key Idea 7: Human decisions and activities have had a profound impact on the physical and living environment.

Performance Indicator 7.1 Describe the range of interrelationships of humans with the living and nonliving environment.

7.1a The Earth has finite resources; increasing human consumption of resources places stress on the natural processes that renew some resources and deplete those resources that cannot be renewed.

7.1c Human beings are part of the Earth’s ecosystems. Human activities can, deliberately or inadvertently, alter the equilibrium in ecosystems. Humans modify ecosystems as a result of population growth, consumption, and technology. Human destruction of habitats through direct harvesting, pollution, atmospheric changes, and other factors is threatening current global stability, and if not addressed, ecosystems may be irreversibly affected.

Performance Indicator 7.3 Explain how individual choices and societal actions can contribute to improving the environment.

MEDIA COMPONENTS

Video

NATURE: The Secret World of Sharks and Rays, selected segments

Clip 1: “Shark and Turtle”

A battle between a loggerhead turtle and a shark.

Clip 2: “Unlikely travel companions”

A variety of symbiotic relationships exist between sharks and other marine species.

Clip 3: “Sharks and fishermen”

Sharks and fishermen compete for the same catch.

Clip 4: “Collapse of sharks”

This clip shows the destructiveness of the shark fin and shark cartilage industries.

Clip 5: “Sharks in our future”

If sharks can be shown to have value while alive, their future may be bright.

Access the streaming and downloadable video segments for this lesson at the Video Segments Page.

Web sites

Malaria games from nobelprize.org
This site provides two games – the mosquito game and the parasite game – to help students understand the transmission of malaria.

Life Cycle of a Malaria Parasite Interactive Tour
This flash-based interactive tour provides a detailed explanation of each stage of the malaria parasite’s life cycle.

MATERIALS

For each student:

• Ecological Relationships Student Organizer (PDF) (RTF)

For each group (3-4 students):

• Malaria Student Organizer (PDF) (RTF)
• Computer with Internet access
• Ecosystem Action Plan Student Organizer (PDF) (RTF)

For the teacher:

• One computer with Internet access for class demonstration
• Teacher Answer Key (PDF) (RTF)
• Ecosystem Action Plan Assessment Rubric (PDF) (RTF)

PREP FOR TEACHERS

Prior to teaching this lesson, you will need to:

Preview all of the video clips and Web sites used in the lesson.

Download the video clips used in the lesson to your classroom computer, or prepare to watch them using your classroom’s Internet connection.

Bookmark the Web sites used in the lesson on each computer in your classroom. Using a social bookmarking tool such as del.icio.us or diigo (or an online bookmarking utility such as portaportal) will allow you to organize all the links in a central location.

Gather the necessary materials as outlined above in “Materials” in advance of teaching the lesson.

Next: Proceed to Activities

Taking a walk through the Amazon rainforest? Might want to keep an eye out for what look and sound like cannonballs, crashing down from above at more than 50 miles an hour. If you are unlucky enough to be in the way, you could end up dead — or at least severely dazed!

The balls, which can weigh up to 5 pounds, aren’t really fired from a cannon. They are actually the fruit of the Brazil nut tree, one of the most marvelous and mysterious trees in the rainforest. Each ball-shaped fruit or pod holds up to two-dozen seeds we conventionally know as Brazil nuts.

For centuries, however, Brazil nut trees presented a puzzle to biologists. For one thing, they couldn’t figure out what kind of animal was able to break open the rock-hard fruits so that the nuts could sprout into new trees. For another, it wasn’t clear why only trees in undisturbed forests bear fruit.

As NATURE’s Deep Jungle: Monsters of the Forest shows, researchers have begun to solve the Brazil nut’s mysteries. In addition to learning more about the tree’s mysterious existence, viewers get a look at one of the Brazil nut’s archrivals — the incredible strangler fig, which can choke a huge Brazil nut tree to death within a few decades.

Brazil nut trees are among the giants of South America’s Amazon. They tower up to 200 feet high, and their spreading branches and flowers provide habitat and food for numerous forest creatures. The Brazil nut is also the foundation of a global business worth $50 million a year. Collectors harvest the nuts by gathering fallen pods and chopping them open with sharp tools. A single mature tree can produce more than 250 pounds of nuts a year.

But how do the nuts get free from their rock-solid pods in the wild? No Amazon creature, it seemed, had jaws powerful enough to crack open the cannonballs.

One answer, it turns out, is the agouti — a small mammal that looks a bit like a large guinea pig. Agoutis have small, chisel-like teeth that can penetrate the Brazil nut’s seed case. They eat some of the nuts. But, just as important, they carry away and bury others for future meals. If forgotten, these seeds can stay dormant in the soil for years, waiting for the perfect conditions to germinate and grow into a new Brazil nut tree.

The agouti isn’t the only animal that Brazil nut trees need to survive. It appears that they also rely on certain bees, and even other plants, to reproduce. Orchid bees visit flowering Brazil nut trees to collect nectar; as they buzz about feeding, the bees inadvertently carry pollen from tree to tree, fertilizing the flowers and helping the trees produce nuts. For the bees to survive, however, the males must attract mates, and to do that, the male bees need fragrance from a particular orchid to attract female bees. If the forest is damaged and the orchids disappear, so will the bees — and the Brazil nuts.

Forest disturbance isn’t the only threat to Brazil nut trees. Competition also comes from a sneaky plant known as the strangler fig tree. Strangler figs start out as tiny, almost invisible seeds deposited on a branch by small mammals or birds. The seed sprouts, and a tiny root gains a foothold. It’s the beginning of the end.

Eventually, the root creeps down the trunk to the forest floor, stealing water and nutrients from the tree through its bark as it goes. More roots soon join in, wrapping tight around the Brazil nut tree, encasing its victim. Ultimately, over decades, the tree dies, leaving the fig standing like a hollow monument to this epic struggle.