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)
Watch the video, taking notes about:
- the biological interactions
- the experimental strategies developed by the scientist
- 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.
- Explain why the system is an example of top-down control.
- Explain the trophic cascade in the system.
- 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.