Drawing a food web
(adapted from Nelson Biology Units 1 and 2 Activity Manual: Activity 11.1)
Introduction
A food web is a network of food chains, showing how organisms get their food and energy
from other organisms.
Purpose
To construct food webs from second-hand data.
Procedure
Part A – A pond community
Organisms
Carp
Prawns
Snails
Flycatchers (bird)
Pond flies
Frogs
Kingfisher (bird)
Waterbird
Turtles
Dragonflies
Trout
Water snake
Food
Algae, water weeds
Algae, water weeds
Algae, water weeds
Dragonflies, pond flies
Decomposing water weeds
Dragonflies, pond flies
Carp
Snails, Prawns
Snails, Water weeds
Pond flies
Carp, prawns
Frog eggs, chicks of kingfisher and flycatchers
Use the above data to draw a food web of the pond community. Arrows between the
organisms should indicate the direction in which the energy (food) travels.
Discussion Questions
1. Identify and label all the producers, first and second order consumers. Explain
how you made your selections.
2. Fertilisers from nearby farmland wash into the pond after heavy rain. This
causes a blue-green algae bloom in the pond. How would this affect the
inhabitants of the pond?
3. A biological control in the form of a virus is introduced to control the population
of carp in the pond. What would be the effect of a reduction in carp numbers on
the food web?
Part B – A Mangrove community
Mangroves flourish in warm, shallow water environments around Australia. They can
produce about 10 tonnes of organic matter per hectare annually. The leaves, fruits and
woody parts of the grey mangrove (Avicennia marina) fall from the tree into the water where
they are broken down by bacteria and fungi. It may take a year for a leaf to be completely
broken down. Crabs, prawns, worms and snails feed on the bacteria and fungi and in turn
may be eaten by larger animals such as the white-faced heron. The bullseye fish feeds on the
decaying leaves and itself provides food for the pelican. Ultimately the organic matter
produced by mangroves provides for human consumption in the form of the fish, crabs and
prawns caught by the rich estuarine fisheries.
Construct a food web of the mangrove community using the above description.
Discussion Questions
1. Identify all the producers, first and second order consumers in the food web of
the mangrove community. Explain how you made your selections.
2. Chemical analysis of the area carried out by scientists has identified a high level
of heavy metals in the water of the mangrove. Suggest the impact that a heavy
metal such as mercury may have on the organisms in the food web.
3. Mangroves are often located in beachfront areas of our coastline. These areas
are highly sought-after for the development of housing for humans. What would
be the long-term effects of clearing mangrove areas to allow for urban
development? Explain.
Conclusion
Refer back to the purpose of this activity and write a conclusion based on what you have
learnt by undertaking this activity.