A garden food web

A garden food web

Pencil and paperOnline interactive
Overview
Using this Resource
Connecting to the Curriculum
Marking Student Responses
Working with Students
Further Resources
This task is about using diagrams to show information about a garden food web.

Question 1Change answer

garden food web diagram
a)  On the food web what do the arrows represent?

Question Change answer

b)  Use the food web to complete the Venn diagram below, to show which animals eat beans,
     which eat tomatoes, and which eat both.
     The Venn diagram has been started for you, showing that snails eat both tomatoes and beans. 
Drag and drop image target

Question 2Change answer

c)  The gardener uses a spray that kills aphids and white fly.
     Choose 3 different animals in the food web and explain how this will affect them.
1. 2. 3.

Question 2Change answer

d)  Which animal will probably disappear when all the bean plants are pulled out? Why?
Task administration: 
This task can be completed with pencil and paper or online with some auto-marking.
Level:
5
Curriculum info: 
Science, Communicating in science, Living World
Key Competencies: 
Using language, symbols, and texts
Keywords: 
ecology, interdependence, food webs, food chains, venn diagrams, systems thinking
Description of task: 
Task: Use a Venn diagram to interpret a food web based on the vegetable garden. Assessment focus: using diagrams to identify relationships between organisms; using systems thinking to describe these relationships.
Curriculum Links: 
Science capabilities
The capabilities focus is brought about by the conversations you have and the questions you ask.
 
Capability: Interpret representations
This resource provides opportunities to discuss food webs and Venn diagrams and the way they organise data for different purposes.
Science capabilities: 
Interpret representations
Making Better Sense: 
Food Chains
Answers/responses: 
  Y10 (08/2006)
a)

Correct answer: Energy flow through the ecosystem
Partial answer: Recognises that "what eats what" is not an accurate description because arrows are "back to front" for this idea, for example:

  • Are eaten by
  • The arrows lead to the predators of that organism
  • The thing it's pointing to consumes whatever the arrow is coming off

very difficult

moderate
b) easy
c) All animals will be affected to some extent. We looked for accurate descriptions of impacts that suggested:

Conditional systems thinking (recognises that what happens next may not be straightforward to predict)

  • Spider – won't have the aphids or whiteflies to eat so will either die or prey heavily on wasps. Wasps – will either have no spiders eating them (because they died from lack of aphids/whiteflies) or will be eaten a lot more

Simple systems thinking (begins with the most obvious change – usually to spiders – and relates other changes to that)
Spiders: because this now only leaves the spider with one food source: the wasps. So there will be less spiders because there's less food.
Wasp: if there are less wasps because of the hungry spiders, then there will be a decrease in wasp numbers.

Caterpillars: if there's a decrease in wasp numbers then there will be an increase in caterpillar numbers, in turn eating more food, leaving less for others.

 

very difficult

      
difficult
c) Three substantially correct but not linked changes

  Spiders – because spiders eat both aphids and whiteflys their diet will decrease
Caterpillars – because of the diet of aphids and whiteflys there will be more food – tomatoes and beans – for the caterpillar
Snails – the snails diet will increase

NOTE: Some students described one or two correct changes (22%)

 moderate
d)

Beetles because they only eat beans (name and reason)

Some students named beetles but didn't explain (5%).

 easy

 

Diagnostic and formative information: 

Developing a nature of science idea via the key competency "using language, symbols and texts"

As we have found in another recently developed item Feeding relationships in the Southern Ocean most students did not know that the arrows on food webs represent energy flow through an ecosystem. While this is a small point when considered in isolation, learning to ask questions such as "What do these arrows represent"? and "Who decided they should be like that?" is grounded in the nature of science idea that scientists put meaning into symbols in specific ways for particular purposes in specific contexts. Understanding this is one part of developing science-specific competencies in "Using language, symbols and texts".

There is also a practical reason to emphasise this point. When students think arrows represent "what eats what" they can get confused about how to read the systems interactions portrayed in a food web. For example, if part of the food web reads: wasp larvae → spiders → birds, then misinterpretations might look like the following two examples:

Wasps will have no spiders to eat because the spiders won't have any food
(incorrect idea that wasps eat spiders)

If there is more spiders there will be less birds because there is lots more spiders to eat the birds.
(incorrect idea that spiders eat birds)

Six percent of students knew how to "read" the food web but did not complete the Venn diagram correctly. It seems that this type of visual text for representing sets and subsets is not familiar to some students. Features of fish  (Level 4) and Comparing animals (Level 3) also discuss this problem.

Practice in question answering
Some students need more practice in writing answers that are sufficiently specific to clearly explain the effect:

Spiders: spiders will not have a food source.
Birds: birds will not have a food source as well.
Spiders will die of starvation.
Five percent of students described at least one example of an effect on a plant, although the question asked them to consider three animals.

A common misconception
One student told us the question was inappropriate, showing how persistent this well known misconception can be:

There is only one type of animal – birds.  The rest are insect foods and spiders.

Next steps: 
It seems that the majority of Level 5 students can now read a food web as a straightforward system. However real systems are characterised by uncertainty, emergent outcomes, and hence by effects that may not be able to be predicted. "It depends" is a good way to begin thinking about these. Many contemporary environmental debates cannot be understood without grasping the importance of this type of systems thinking.
 
With support, students at Level 5 could be encouraged to develop more conditional thinking, as shown in the example above.  You could scaffold this by asking them to debate "what if.." alternatives for possible changes.

Feeding relationships in the Southern Ocean is about food webs in the Southern Ocean and links these to global warming changes.