Interdependence in the Ecosystem
Enhanced Video Resource

This video segment from Nature: “Salmon: Running the Gauntlet” highlights one region where salmon are abundant (Central Idaho’s Frank Church River of No Return Wilderness) and another where salmon are scarce (near the Hell’s Canyon dam complex on the Idaho-Oregon border), and highlights the important role of salmon in an ecosystem. The segment describes the ways in which different species depend upon each other and, specifically, how species are impacted by the presence and absence of salmon. The segment explains how invertebrates feed on dead adult salmon and, in turn, serve as food for newborn salmon, as well as how bears eat salmon carcasses and spread salmon-generated marine nutrients in the mountains. The segment concludes by highlighting efforts to reintroduce salmon nutrients into streams. (Note: This video contains a graphic scene of a bear killing and eating a salmon, as well as other species feeding on dead salmon.)

Discussion Questions:

Before watching the video:

  • What species do you think might be affected by salmon?
  • In what ways might these species be impacted by the presence or absence of salmon?

After watching the video:

  • In the video, rancher and river guide Jerry Myers says, “You understand by living out here that things are connected and a big, huge part of that is salmon.” Provide examples from the video to support this statement.
  • How do bears, birds, invertebrates and trees each benefit from the presence of salmon?
  • In the video, author David James Duncan states, “As much as any species of plant and animal in the Pacific Northwest, if this creature is removed from the tapestry, the tapestry will unravel.” Provide reasons to support or refute the statement.
  • Why are scientists depositing salmon carcasses and artificial substances into streams? How are they evaluating the impact of these efforts?

Background Essay:

Salmon live in the northern Atlantic and Pacific Oceans. Most are anadromous, meaning they are born in freshwater, migrate to the sea where they live for most of their lives, and then return to freshwater streams to spawn. In recent years, the number of salmon has decreased dramatically due to a combination of natural and human-related factors. In the Colorado River, the salmon population is approximately 3% of what it was in the early 1800s.

Some factors posing threats to salmon are rising stream and river temperatures, due to climate change; pollution, which is damaging and sometimes deadly to salmon and their prey; overharvesting (through commercial fishing, etc.); natural predators; and dams on the rivers, which obstruct passage to spawning areas. For example, the Hells Canyon Complex, located on the Oregon-Idaho border and completed in 1967, includes three dams, which prevent passage of salmon to the Upper Snake River Basin.

When salmon are removed from an ecosystem, the number of grizzly bears decreases. Other species, such as mink, orcas, birds, river otter and microorganisms, which depend on salmon for food, also suffer when the number of salmon declines.  The decrease of these animals, in turn, impacts plant life in forests and mountains. For example, bear droppings and salmon carcasses, which bears leave in the forest and mountains, are rich in both phosphorous and nitrogen, and support plant life. When the number of bears decreases, the amount of salmon-generated nutrients plants receive from bears is reduced as well.

In order to increase the number of salmon, scientists have created fish hatcheries, which produce, raise and release salmon into the wild. Columbia basin hatcheries release more than 100 million salmon into the Columbia River and its tributaries each year.

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National Science Education Standards:

Grades 9-12:

Content Standard C: Life Science
Fundamental concepts and principles that underlie this standard include:
  • The Interdependence of Organisms
    • Energy flows through ecosystems in one direction, from photosynthetic organisms to herbivores to carnivores and decomposers.
    • 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.
    • 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.
    • 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.

Content Standard F: Science in Personal and Social Perspectives and Technology
Fundamental concepts and principles that underlie this standard include:

  • Science and Technology in Local, National, and Global Challenges
    • Humans have a major effect on other species. For example, the influence of humans on other organisms occurs through land use—which decreases space available to other species—and pollution—which changes the chemical composition of air, soil, and water.

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