Purposes
- To reveal students’ ideas about the feeding relationships among organisms in the farm pond ecosystem.
- To help students understand the feeding relationships among the organisms that live beneath the surface of a pond: underwater plants (e.g., hornwort, pondweed), algae, mayfly larvae, minnows, perch.
Description
Students examine the organism populations in the pond model from Part Two and make predictions about feeding relationships among organisms within the pond ecosystem. At this point, it is not necessary for students to record these predictions on their model; however, students may record them elsewhere. Once all students have discussed initial ideas, facilitate a whole-group discussion, encouraging students to provide a rationale for their predictions. You may need to reiterate that organisms that live underwater are of highest interest rather than those that live above the surface, or those who visit the pond. After students have had an opportunity to discuss initial ideas, use student contributions to develop a food web for the organism populations most central to the Sunrise Farm mystery: perch, minnows, mayfly larvae, underwater plants (e.g., hornwort, pondweed), algae, decomposers.
Questions to Ask Students
- Look at your pond model. What are some ways that the organisms in your model are important to each other?
- Do most organisms consume just one thing or many different things?
- Does more than one kind of organism consume the same thing?
- Which organism(s) consumes the producers?
- How can we show who consumes who?
- What direction should the arrow point? What does the direction of the arrow mean?
- Why is it important to have the arrow pointing in the correct direction?
- What do decomposers consume?
- How can we represent decomposers?
- In what ways is your model similar to a real pond? How is it different?
Student Thinking
- Students may initially think that the organisms in the pond rely on humans to provide their food.
- Students may believe that organisms consume all others below them in a food web. For example, students might think that perch consume underwater plants and algae, in addition to minnows and mayfly larvae.
- Relatedly, students may think that organisms choose from among many options in selecting their prey or easily change their diet based on food. For example, they may think that if mayfly larvae were not available, that minnows would consume algae. These ideas may arise from students’ own experiences of selecting food at a grocery store or restaurant.
- Students might think about food web relationships at the individual level (e.g., a single predator animal and a single prey animal), as opposed to the population level. For example, students may envision a relationship as one perch consuming one minnow, as opposed to the perch population feeding on the minnow population. For this reason, it may be helpful to support students in attending to the way they’ve represented the population versus a single organism in their pond diagram.
Implementation Tips
- Because students will draw organisms in various locations in their pond diagram, it may be helpful to use a food web representation.
- Representing decomposers in a food web can be difficult. As shown below, one approach is to orient decomposers vertically (but with no arrows) to represent activity at all levels of a food web.
