Teacher Preparation

Overarching learning goal: Through this activity students will be able to understand the differences between food chains, food webs, trophic levels and trophic relationships. They will also understand that different ecosystems are comprised of unique food webs and trophic relationships. They will learn that climate change will have impacts on the integrity of food webs and that although the impacts of climate change will affect different organisms in different ways, the whole food web will affected.

Teacher content information: Food webs are a way of expressing the transfer of energy (or feeding relationships) in an ecosystem. For example: a plant gets its energy from the sun; another animal gets its energy from grazing on the plant; and, another animal gets its energy from eating that animal, and so on in a chain.

But what happens when one of the animals in a food web suffers a decline in numbers or is completely removed? How does this affect all the other animals in the food web?

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Some prior understanding of food webs and trophic levels will be useful for students in this activity. This activity could be used: Schools Tree Day - Schoolyard food webs.

Remind students that in a food chain we represent the flow of energy using arrows. The arrow should always point to the animal that has just eaten something. This is because it shows the flow of energy.

Download and cut up the animal names (click here to download) for the reflection activity prior to the class.

Student and classroom organisation

Step 1.

Begin this activity by asking students to refresh their understanding of food webs and trophic levels.

What is a food chain? Give an example. (Suggested answer: A food chain is a linear representation of how organisms get energy and pass energy on to other organisms. A food chain shows just one line of energy transfer, for example, from flower to butterfly to bird.)
What is a food web? Give an example. (Suggested answer: A food web is a linear representation of how organisms within an ecosystem receive and transfer energy. It is a more complex representation as it shows a range of organisms and how they all interact with one another. An example of a food web could be a grassland ecosystem where plants, insects, reptiles, mammals and birds all interact with one another and transfer energy.)
What do we mean by trophic levels? Give an example. (Suggested answer: A trophic level refers to the position an organism occupies in the food chain. For example, a primary producer - such as a plant - is at the bottom of the food chain. A carnivore is at the top of the food chain.)

Step 2.

Ask for one or two student volunteers to come to the board and draw an African grassland food web under instruction from the class, including the flow of energy between organisms and the relevant tropic levels (will include Decomposers, Producers, Herbivores/Omnivores, Carnivores, and Scavengers). Allow 3 minutes for the creation of the food web.

The food web should include the following organisms:

Organism	Trophic level
Acacia	Producer
Baboon	Omnivore
Bacteria	Decomposer
Cheetah	Carnivore
Dung beetle	Decomposer
Fungi	Decomposer
Giraffe	Herbivore
Grass	Producer
Hunting dog	Carnivore
Hyena	Scavenger
Impala	Herbivore
Leopard	Carnivore
Lion	Carnivore
Termites	Herbivore/Omnivore
Vultures	Scavenger
Wildebeast	Herbivore/Omnivore
Zebra	Herbivore/Omnivore

Step 3.

Explain to students that in the next part of the activity you will be looking at how climate change might impact upon food webs. Break the class into groups and assign groups with one of the following ecosystems:

Antarctic ecosystem
Coral reef ecosystem
Wetland ecosystem
Desert ecosystem
Rainforest ecosystem

Ask students to research their ecosystem and its food web. They must then look at what the projected climate change impacts will be on their ecosystem (research resources provided on the Student Worksheet).

Groups should create a short movie or animation that describes their ecosystem, how the food webs in this ecosystem currently function, and how climate change will affect this ecosystem. The film or animation should run for about one to one and a half minutes. Ask students to think about how they can present their information in the most engaging way: Will it be a story? Or a documentary? Or a simple presentation of the facts?

Students can use existing movie or animation programs on their computers, or one of the following online programs (free but will require registration):

Step 4.

Ask students to present their film or animation to the class. Ask students to use the Peer Assessment Rubric to evaluate each others presentations (available on the Student Worksheet). Alternatively, students could publish their film on Vimeo and encourage peers to leave constructive comments.

Assessment/Reflection

1. Cut up and distribute the animal names (click here to download), ensuring that each animal is accounted for. Stand the students and their species in a circle and give the ball of string to a participant. Holding onto the end of the string they should passes the ball of string to another participant who they depend upon to exist. The string is passed from one to another who is dependent for survival. A web develops within the circle.

Once all animals have been included in the web, ask students not participating to nominate a species to sit down - it has just gone extinct. On sitting ask all who are directly connected to the lost species sit too. Then ask those you are connected to those who have just sat to also sit down.

2. Ask students to answer the reflection questions on the Student Worksheet.

Extension

1. Ask students to imagine they are a journalist reporting on how humans can influence the resilience of ecosystems and food webs. Students should write a short article with an opening statement and supporting paragraph, at least three dot points on actions humans can take, and a concluding statement/call to action.

2. Ask students to look again at the African grassland food web and to create a poster or mind map (using bubbl.us or mindmeister) showing how this food web will be affected by climate change.

Earth Hour - How Will Climate Change Affect Food Webs?

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