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Food Web Disruption

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Food Web Disruption

Read the field notes and study the food-web table. Arrows mean “is eaten by”: energy moves from the organism at the arrow’s tail to the organism at its point. Use evidence from the notes and table in your answers.

Field notes: Pelican Creek

A group of students surveys a freshwater wetland in Australia. Reeds and algae are producers: they make their own food using sunlight. Insect larvae eat algae and plant material. Small native fish eat insect larvae. Frogs eat insect larvae too, while waterbirds eat small fish and frogs. A fox has recently begun visiting the wetland and preys on frogs and waterbirds. After a nearby drain is widened, the wetland becomes shallower and some reed beds disappear. The students notice fewer insect larvae and frogs during their next survey. They wonder whether the habitat change, the fox, or both may be affecting the food web.

Food (energy source)

→

Eater

Reeds and algae

→

Insect larvae

→

Small native fish

Insect larvae

→

Frogs

Small native fish

→

Waterbirds

Frogs

→

Waterbirds and foxes

Waterbirds

→

Foxes

Analyse the disruption

Use the field notes and food-web table to investigate how changes can spread through an ecosystem.

1.Which organisms in the Pelican Creek food web are producers?

2.Select the best explanation of what the arrows in the food-web table show.

The direction animals travel through the wetland
The direction energy moves, from food to eater
Which organism is the largest
Which species live closest together

3.Complete the energy pathway using organisms from the table: reeds and algae → → small native fish → .

4.After the drain was widened, reed beds shrank. Explain one possible reason why this habitat change could lead to fewer insect larvae.

5.The students record fewer insect larvae. Predict one possible effect on small native fish and explain the link.

6.A student says, “If frogs decrease, nothing else in this food web will change.” Is this statement true or false? Use one feeding link to support your answer.

TrueFalse

7.Foxes prey on frogs and waterbirds. If fox numbers increase, predict one possible change to the populations of these prey species. Explain why the prediction is not certain.

8.The students have one week to investigate why frog numbers fell. Which is the fairest test?

Count frogs once at one spot and decide the fox caused the change
Count frogs at several wetland sites, repeat counts, and record reed cover and fox evidence at each site
Ask one person which animal they think is responsible
Remove all the foxes and see what happens

9.Suggest one practical action that could help the wetland food web recover, and explain which part of the disruption it addresses.