Skip to main content
HHMI BioInteractive
  • Español
  • Site Search
  • Log In/Create Account
  • BioInteractive Resources
  • Planning Tools
  • Professional Development
  • About Us

Some Animals Are More Equal than Others: Keystone Species and Trophic Cascades

Topic

  • Ecology
  • Communities
  • Ecosystems
  • Matter & Energy
  • Scientific Skills & Literacy
  • Experimental Design

Resource Type

  • Videos
  • Short Films

Level

High School — GeneralHigh School — AP/IBCollege

Duration

00:19:29
Saved By
122 Users
Share This
View in Spanish

Description

This film tells the story of the ecologists who first documented the role of keystone species in ecosystem regulation.

Some Animals Are More Equal than Others explores the work of ecologists Robert Paine and James Estes. Robert Paine’s experiments showed that removing starfish from tidal pools has a big impact on the population sizes of other species. James Estes and colleagues discovered that the kelp forest ecosystems of the North Pacific are regulated by the presence or absence of sea otters, which feed on sea urchins that consume kelp. These direct and indirect effects of starfish, sea otters, and other so-called keystone species describe a phenomenon known as a trophic cascade. These early studies were the inspiration for hundreds of subsequent investigations on how population sizes are regulated in a wide variety of ecosystems.

The “Abbreviated Film Guide” provides a short summary of the film, along with key concepts and connections to curriculum standards.

An audio descriptive version of the film is available via our media player.

Student Learning Targets

  • Use evidence to explain why some species play the role of keystone species in their ecosystems.
  • Explain the concept of a trophic cascade using examples from different ecosystems.

Key Terms

apex predator, food web, herbivore, keystone species, trophic cascade

Primary Literature

Dyer, Lee A., and Deborah K. Letourneau. “Trophic cascades in a complex terrestrial community.” Proceedings of the National Academy of Sciences 96, 9 (1999): 5072–5076. https://doi.org/10.1073/pnas.96.9.5072.

Estes, James A., Martin T. Tinker, Terrie M. Williams, and Daniel F. Doak. “Killer whale predation on sea otters linking oceanic and nearshore ecosystems.” Science 282, 5388 (1998): 473–476. https://doi.org/10.1126/science.282.5388.473. To access this article, set up a free AAAS account.   

Terms of Use

Please see the Terms of Use for information on how this resource can be used.

Accessibility Level (WCAG compliance)

PDF files partially meet criteria. Video files meet criteria.

Version History

Date Published 04.01.16
Date Updated 11.05.21

NGSS (2013)

HS-LS2.A, HS-LS2.B, HS-LS2.C, HS-LS4.C

AP Biology (2019)

ENE-1, ENE-4, SYI-1, SYI-2, SYI-3

IB Biology (2016)

4.1, 4.2, C.1, C.2, C.3, C.4, C.5

AP Environmental Science (2020)

Topic(s): 1.1, 1.11, 2.7

IB Environmental Systems and Societies (2017)

2.2, 2.3, 2.4, 3.3

Vision and Change (2009)

CC4, CC5

Materials

HD (M4V) 744 MB
HD (WMV) 605 MB
SD (M4V) 164 MB
SD (WMV) 165 MB
Transcript (PDF) 152 KB
Abbreviated Film Guide (PDF) 752 KB
Spanish dub (MP4) 313 MB
Transcript - Español (PDF) 313 KB
Abbreviated Film Guide - Español (PDF) 232 KB

Use This Resource With

Activity Resource
Activity for Some Animals are More Equal than Others
Activity Resource
Modeling Trophic Cascades

Educator Tips

Hear how educators are using BioInteractive content in their teaching.
Educator in front of an image of a rocky coast Play Video Next Slide Next Slide
/
1-Minute Tips

Trophic Cascades

Tim Guilfoyle describes how he uses the BioInteractive short film "Some Animals Are More Equal than Others" and a claim-evidence-reasoning activity to have his students examine Robert Paine's starfish exclusion experiment.
View Article
Previous Slide Next Slide
Close Modal

Explore Related Content

Other Resources About Science History

Showing of
Screenshot from the video of Mary Leakey
Animated Shorts
Animated Life: Mary Leakey
Image from the video of Lattimer with a coelacanth
Animated Shorts
Animated Life: The Living Fossil Fish
Image from the activity
Phenomenal Images
Written in Chalk
Image of a starfish
Film Activities
Activity for Some Animals are More Equal than Others
Screenshot of CGI dinosaurs reacting to the asteroid strike
Film Activities
Activity for The Day the Mesozoic Died
Photo of an icefish in sub-freezing water
Short Films
The Making of the Fittest: The Birth and Death of Genes
Two bear cubs walking on their hind legs crossing a road
Short Films
From Ants to Grizzlies: A General Rule for Saving Biodiversity
Image from the film of Wegener with a sled dog
Animated Shorts
Animated Life: Pangea
Image from the video
Clips
The Discovery of Ribozymes
Image from the film
Lessons
Identifying Patterns in Observations
van Leeuwenhoek examining a microscope
Animated Shorts
Animated Life: Seeing the Invisible
Image of Darwin drawing his tree diagram from the film
Lessons
Reading Primary Sources: Darwin and Wallace
Image of Darwin from the film
Short Films
The Origin of Species: The Making of a Theory
Title screen of the film
Short Films
The Double Helix
Image from the film of DNA forming a double helix
Film Activities
Activity for The Double Helix
Image from the film of AR Wallace
Animated Shorts
The Animated Life of A. R. Wallace
Image of Darwin and his maid from the video
Film Activities
Activity for The Making of a Theory
Photo of a manatee with bone structure superimposed
Lessons
The Making of a Theory: Fact or Fiction
Image from the activity
Lessons
Pulse Chase Primer: The Meselson-Stahl Experiment
A map from the Wallace line activity.
Lessons
Discovering the Wallace Line

Other Resources About Keystone Species

Showing of
Image from the film of a survey plane flying over land.
Click & Learn
Survey Methods
Image of a starfish
Film Activities
Activity for Some Animals are More Equal than Others
Photo of wildebeest silhouetted by the setting sun
Short Films
Serengeti: Nature’s Living Laboratory
Montage of keystone species from the interactive
Click & Learn
Exploring Keystone Species

Other Related Resources

Showing of
Image of a starfish
Film Activities
Activity for Some Animals are More Equal than Others
Varias cebras sobre un pastizal.
Card Activities
Creating Chains and Webs to Model Ecological Relationships
Image from the film of Mary Power measuring the depth of a stream.
Scientists at Work
Riverine Food Webs: How Flow Rates Affect Biomass
Image from the film of Silliman inspecting grasses.
Scientists at Work
Trophic Cascades in Salt Marsh Ecosystems
Trophic cascade thumbnail
Click & Learn
Exploring Trophic Cascades
Photo of a jaguar
Card Activities
Modeling Food Webs in Darién, Panama
Screenshot from the interactive
Click & Learn
Exploring Biomass Pyramids
Photo of a lion taken from a trail camera
Click & Learn
WildCam Lab
Photo of a tapir
Click & Learn
WildCam Darién
Trail camera image of a lion
Click & Learn
WildCam Gorongosa
HHMI BioInteractive
  • Facebook
  • Instagram
  • Twitter
  • YouTube
  • Newsletter Signup
  • HHMI.org
  • Terms of Use
  • Privacy Policy
  • Accessibility