This focus idea is explored through:
Contrasting student and scientific views
Student everyday experiences
Students are often unaware that on a food web a named organism represents a population rather than a single individual; for example, a population of rabbits or foxes rather than a single rabbit or single fox. It is also common that they do not see food webs as having a complex interconnection of relationships but as a series of simple, unconnected food chains. Students are also often less aware of relationships between organisms other than feeding relationships. When asked to predict the consequences of the removal of one organism from a food web the students often consider only the changes that occur along one food chain, not realising the possible impact the removal of the organism could have on multiple pathways in the food web.
Research: Wood-Robinson (1985)
It is also common for students to believe that if organisms are separated in the food web so they are not directly related in a ‘predator–prey’ relationship, changes in one population will not affect the other.
Many students also believe that if an organism is positioned higher in the food web it will be a predator of all the organisms positioned below it in the food web and that if the size of one population of organism changes it will have no effect on the size of the population of its predator.
Research: Griffiths & Grant (1985)
Interrelationships between living organisms and their environment are complex and interdependent. All organisms are part of complex food webs that include both plants and animals. The predator-prey inter-relationship is common. Some species are highly dependent on others (for example, pandas or koalas can eat only certain species of grasses/trees) while others are so closely linked that their survival may be dependent on just a single species (for example, there exists a species of wasp that nests only in the fruit of a type of fig tree and is the only insect that can pollinate the flowers of the tree).
Critical teaching ideas
- All organisms, both land based and aquatic, are interconnected by their need for food.
- The network of interactions is referred to and represented as a food web.
- Food webs can be used to illustrate the interdependence of organisms in a particular environment.
- A food web typically describes the feeding relationships, beginning with species capable of producing ‘food’ from an energy source and organic materials (i.e. plants) connected to the animals that eat them and then the animals that eat those animals and so on. Relationships other than the ‘predator–prey’ feeding relationship do exist.
- Models and simulations provide useful visual representations which can be used to build understanding of the various interactions that take place between living things in their environment. For example, simulations can show the effects of altering conditions like weather.
Explore the relationships between ideas about interactions between organisms in ecosystems in the
Concept Development Maps – (Flow of Energy in Ecosystems, Flow of Matter in Ecosystems)
The notion of a food web within an ecosystem is a much more difficult concept than a food chain because of its complexity. Students need to be aware that organisms within a food web exist in a hierarchical structure with organisms at lower levels often able to produce their own food and organisms at higher levels existing as consumers. It is important to provide students with the opportunity to consider the factors that influence the survival of individual organisms and for them to appreciate that not all plants and animals survive equally well in all habitats.
The following activities build a game – ‘The Rock Pool Game’ - that can create many opportunities for conceptual development.
Open up discussion via a shared experience
To create a food chain role play such as ‘The Rock Pool Game’, you will need to firstly identify the plants and animals involved in the food chain. Examples of organisms that live in or depend on rock pools are seaweed, crabs, fish and seagulls. In this simple food chain the crabs eat the seaweed, the fish eat the crabs and the seagulls eat the fish. In the game a nominated area in the classroom becomes the rock pool. Seaweed is represented on cards and these are distributed around the rock pool area. Students are divided into seagulls, fish and crabs and stickers or badges are worn to clearly identify each animal. Every crab needs to carry a collection bag, such as a brown paper bag.
Mark out a physical area that will be the extent of the environment (the rock pool). Make sure you allow plenty of space.
Create a set of seaweed cards (approx 150 cards for a total of 30 players) and scatter these around the perimeter of the rock pool area. Advise students (now tagged as seagulls, fish and crabs) to stay within the rock pool area.
In the designated time each animal must ‘collect’ the food of their choice. This is done by ‘tagging’ the animal that they need for food and linking hands with them. The crabs must collect seaweed cards and place these in their own collection bags while trying to avoid being eaten by fish and seagulls. The fish aim to ‘tag’ crabs and take their bags. Seagulls aim to ‘tag’ fish and take the bags they have collected.
Make one round of the game last for no more than five minutes or until one group of organisms has been eaten, such as all fish have been tagged.
Devise a way of showing how each animal becomes linked when one has tagged the other. For example, when tagged (eaten) the prey could hold on to arm of the predator, eventually forming a chain. It may be useful to begin with equal numbers of certain animals and vary these numbers in progressive rounds of the game.
Set food targets for each animal in the food chain; for example, say that to survive a crab needs to have 10 seaweed cards in their bag, whereas seagulls and fish need a total of 50 seaweed cards in their chain. Animals with less will starve to death.
Investigate a variety of marine food chains at:
Help students work out some of the scientific explanation for themselves
Discuss with students their understanding of why they survived or were eaten in the rock pool game. Encourage them to think in terms of the organism that they represented. Discuss how the game is similar or different to real life. Encourage students to identify the factors that contribute to the survival of various organisms in the role play, for example, changing the initial population influencing the availability of food source. List these ideas and refer to these again to make modifications to the design of the role play.
Clarify and consolidate ideas for communication to others
Identify and represent the key interactions in the modelled food chain. Students devise a way of visually representing the connections of the various organisms in the food chain. Students share their representation with peers and critically evaluate the representations. Encourage students to question how the plants or animals are connected.
Focus students’ attention on overlooked detail
Encourage students to recognise and articulate further factors that may contribute to survival, such as size or removal of specific populations, movement, agility, and change in climate. Return to the list from the previous activity and invite students to suggest changes to the game that may assist the survival of certain plants and animals, such as staggering the release of the organisms so that some have more time to collect food before others enter the game. What difference does this change make to the survival of other animals in the game? What happens to the chain if one population does not survive? What are the advantages or disadvantages to the other organisms in the food chain if these animals survive?
Promote reflection on and clarification of existing ideas
Challenge students’ ideas further by increasing the complexity of a problem: introduce a poison into the food chain; this could be a label placed in a secret place on certain animals or plants. At the completion of the game any chain of organisms that have this card will not survive. Students discuss and explore the possible implications of the introduction of this card to the game. Carry out the role play under these new conditions and discuss observations. Students could discuss how successful this game is at modelling the complex nature of food webs.
Open up discussion via a shared experience
Another engaging role play is ‘The Food Chain Drama’. It provides a fun way to introduce junior classes to the idea of food chains and food webs and can be done with up to 30 students (just!).
Give all students in the class a number. There should be approximately two students with fives, three students with fours, four students with threes, five students with twos and the remainder of the students are given ones.
Students numbered ‘fives’ can tag fours, threes, twos, but not ones.
Students numbered ‘fours’ can tag threes and twos, but not ones or fives.
Students numbered ‘threes’ can tag ones and twos and fours.
Students numbered ‘twos’ can only tag ones.
Students who are ‘ones’ cannot tag others and can only be tagged by ‘twos’ and ‘threes’.
Tell students their number and get them to tag a numbered person they are allowed to tag by the rules. If you are tagged by the correct numbered person, you must sit down.
As a class, observe what is left. Discuss how this happened.
Now change the numbers to names:
- 1 = plants
- 2 = herbivores
- 3 = omnivores
- 4 = small carnivores
- 5 = large carnivores
Play the game again so that large carnivores have to behave as fives, plants as ones etc. What is the outcome this time? Why? How?
As a follow up, students may replace the categories with specific plants and animals to complete the exercise. Decomposers as sixes (able to tag everyone once they have BEEN tagged) can now be introduced. To avoid chaos, don't have too many decomposers! Finally, students may draw up a couple of food chains in their workbook based on the tags they have given or received.
This activity has been reproduced with permission of Peel Publications, Australia, Copyright © 2007.
Science related interactive learning objects can be found on the
FUSE Teacher Resources page.
To access the interactive learning object below, teachers must login to FUSE and search by Learning Resource ID:
Ecosystem balance – Students explore how plants and animals interact in three Tasmanian ecosystems: a dry forest, rainforest and seaweed community. They view species descriptions of the plants and animals that live there. They can increase or decrease the population of a species and compare the effects on other species within the ecosystem.
Learning Resource ID: FRZ5RA