Food Chains and Trophic Cascades

In this activity students will watch a video then extract information to construct a food chain. At the same time they will learn about bottom-up and top-down control of systems and a simple trophic cascade in a salt marsh ecosytem.

The video is from the excellent HHMI Biointeractive.

Video about Trophic Cascades in Salt Marshes (10 mins)


Student Task

Watch the video, taking notes about:

  • the biological interactions
  • the experimental strategies developed by the scientist
  1. Now draw the food chain from this system, labeling producer, herbivore and carnivore, 1st, 2nd and 3 trophic levels, and primary consumer and secondary consumer.
  2. Explain why the system is an example of top-down control.
  3. Explain the trophic cascade in the system.
  4. How did the scientist control his experiments?

Approaches to Teaching

I'm going to use this as an introduction to food chains but with a link to trophic cascades which we've just looked at with the  2.1 Yellowstone National Park Wolves exercise. It's a very simple food chain but students will have to extract this from the information provided. It also introduces them to a potentially new type of ecosystem, building up their general knowledge.

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