Endangered Relationships
Lesson Overview

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TOPIC/SUBJECT MATTER: Life Science/Environmental Science

TIME ALLOTMENT: 1-2 45-minute class periods


This lesson uses video segments from the NATURE film “Crash: A Tale of Two Species” to explore the interrelationship between the horseshoe crab and a small migratory bird called the red knot. Both species are in decline, and the red knot’s future, in particular, depends on the horseshoe crab making a comeback in the waters of the Delaware Bay.

Students will first be introduced to the horseshoe crab via a video segment, learning that the species’ longevity (350 million years) makes the horseshoe crab a “living fossil,” an anomaly in terms of the Earth’s species. They will view several other video segments to explore the interconnectedness between the horseshoe crab and the red knot, following the videos with a discussion of the reasons for the decline of each species. Students will fill out an exit ticket to assess their comprehension of these concepts. An optional additional video segment can be used to explore how humans have come to depend on horseshoe crabs as well (their blood, which evolved to have primitive antibacterial properties, is used to test intravenous drugs for contamination).

As a culminating activity, students will use an interactive online map to research endangered species in the region of the United States where they live. They will discuss the environmental changes that have led to the species’ decline (often of human origin) and will discuss the strategies being employed to prevent their extinction.



NATURE: Crash: A Tale of Two Species (selected segments):

Clip 1: “The Living Fossil”

The horseshoe crab has survived for 350 million years.

Clip 2: “Horseshoe Crabs and Red Knots”

Horseshoe crabs are an essential source of nutrition for migrating birds.

Clip 3: “Protecting the Horseshoe Crab”

Measures have been undertaken to protect the horseshoe crab.

Clip 4: “Horseshoe Crabs and Humans”

The horseshoe crab has immense value to humans for its uses in medical technology.

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

Web sites

Sierra Club Endangered Species Map

This interactive map provides information on key endangered species, including efforts currently being undertaken to protect them, in different regions of the United States.


National Science Education Standards

LIFE SCIENCE: Content Standard C

As a result of their activities in grades 5-8, all students should develop understanding of

  • Diversity and adaptations of organisms
    • Biological evolution accounts for the diversity of species developed through gradual processes over many generations. Species acquire many of their unique characteristics through biological adaptation, which involves the selection of naturally occurring variations in populations. Biological adaptations include changes in structures, behaviors, or physiology that enhance survival and reproductive success in a particular environment.

o        Extinction of a species occurs when the environment changes and the adaptive characteristics of a species are insufficient to allow its survival. Fossils indicate that many organisms that lived long ago are extinct. Extinction of species is common; most of the species that have lived on the earth no longer exist.

As a result of their activities in grades 9-12, 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.
    • 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.


As a result of activities in grades 5-8, all students should develop understanding of

  • Populations, Resources, and Environments
  • When an area becomes overpopulated, the environment will become degraded due to the increased use of resources.
  • Causes of environmental degradation and resource depletion vary from region to region and from country to country.


For each student:

  • Endangered Relationships Exit Ticket (PDF) (RTF)

For each group of 3-4 students:

  • One computer with broadband internet access

For the class:

  • One computer for the teacher with a digital projection system


Students will be able to:

  • Describe characteristics of the horseshoe crab;
  • Specify how “living fossils” like the horseshoe crab differ from most other species;
  • Understand that over 99% of all species that have ever existed on earth are extinct;
  • Name specific factors that can lead to species endangerment and extinction;
  • List several strategies that can be undertaken by humans to protect endangered species;
  • Provide at least one example of species interconnectedness: how the population decline of one species adversely affects another species.

Prep for Teachers

Prior to teaching this lesson, you will need to:

Preview all of the video segments 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.

Print and cut out a copy of the “Endangered Relationships Exit Ticket” for each student.

Next: Proceed to Activites

  • Lindsay

    This is GREAT info for my 8th grade interdependence project! It is nicely organized and ready to use.

  • Adam

    I can’t wait to use this in my high school Ecology class. Thank you so much for providing the video and lesson plan. Yall are a gift indeed.

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