Activity for Some Animals are More Equal than Others
This activity explores the content and research discussed in the film Some Animals are More Equal than Others, which tells the story of the ecologists who first documented the role of keystone species in ecosystem regulation.
The short film 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 “Student Handout” probes students’ understanding of the key concepts addressed in the film. The “Educator Materials” document provides suggested pause points in the film with questions for students, background information, and detailed discussion points; a list of related resources and references; and an answer key for the “Student Handout.”
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.
apex predator, food web, keystone species, trophic cascade
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.
Paine, R. T. “Intertidal community structure: Experimental studies on the relationship between a dominant competitor and its principal predator.” Oecologia 15, 2 (1974): 93–120. https://doi.org/10.1007/bf00345739.
HS-LS2-1, HS-LS2-3, HS-LS2-6, HS-LS4-5; SEP6
ENE-4.B, SYI-1.H, SYI-2.B, SYI-3.F, SYI-3.G ; SP1, SP2, SP4
4.1, 4.2, C.1, C.2, C.3, C.4, C.5
2.2, 2.3, 2.4, 3.3
CC4, CC5; DP1