3.4 Keystone Species

Investigating the Role of Keystone Species

Students need to be able to understand the ecological significance of keystone species. I use this activity as a great review at the end of topic 3. It pulls together concepts from topics 1, 2 and 3.

This activity is largely inspired by the work of HHMI and the video linked below. If you want to know more, read The Serengeti Rules by Sean Carroll. Although not in the syllabus I think the concepts of top down and bottom up control in ecosystems are something that students can understand and they find really engaging.

HHMI has produced its own supporting resources for this topic and I would highly recommend them as they have some data processed exercises. Their resources are here.

Keystone Species: An Investigation

A keystone species plays a much larger role in maintaining the structure of an ecosystems than other species. The star fish regulates the populations of most other species in the Washington State coastal ecosystem. Without the starfish the ecosystem becomes much more simple with shorter food chains and less biodiversity. As the top predator in this ecosystem it is therefore an example of “top-down” regulation.

After watching the HHMI video on the work of Robert Payne the man who first described the concept of Keystone Species and Trophic Cascades and James Estes who discovered the role of sea otters as a keystone species in kelp forest ecosystems, answer the questions below.

Video Link for “Some Animals Are More Equal Than Others: Keystone Species and Trophic Cascades” 

  1. Explain how the concept of primary productivity gives rise to the idea of bottom up control in ecosystems. Give examples from your studies in ESS of ecosystems that have different levels of complexity due to differences in primary productivity.
  2. Describe the scientific investigation that Robert Payne took to discover the role of the Purple starfish in the west coast ecosystem.
  3. Explain how this investigation led to Payne's theory of trophic cascades. Try to support your argument with a food web diagram.
  4. Explain why sea otters were also found to be keystone species and killer whales (orcas) are not.
  5. Discuss the role of keystone species in conservation strategies.

 Keystone Species Worksheet  

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