r i ve r habit at p ack
KEY QUESTION 11
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‘How does the loss of one living thing from
the habitat affect other living things?’
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Objectives
This activity is not compulsory but may be used as an extension activity for more
able or older pupils.
By undertaking the food web activity, pupils should be able to understand that food
webs are much more complex than food chains. They should be able to see that the
loss of one living thing from the habitat can have wide ranging impacts and that
green plants play an important role in supporting the whole habitat.
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Resources
Per pair:
11a Pupil reference - ‘Food web activity’
11b Pupil worksheet - ‘River food web’
• Pencil
Per class:
11c Teacher reference - ‘River food web’
Suggested Activities
1. Recap on what is meant by a food chain. Explain to the pupils that a food chain does not show us
the whole picture in terms of feeding relationships in a habitat. Many species have more than one
type of prey and more than one type of predator i.e. feeding relationships are complex (pupils will
need to have the terms predator, prey and consumer explained to them if they have not come across
them before).
2. Explain to the pupils that they are going to construct an example of a river food web. Give each pair
a copy of resources 11a and 11b and a pencil. They need to use the information on resource 11a to
build up their food web by focussing on one component at a time and drawing arrows from the
‘food source’ to the consumer in each case (see worked example 11c). The role of the sun as a food
source for plants will need to be highlighted.
3. Once pupils have completed their food webs, ask them for some general observations. They should
be able to see that food webs are a) complex and b) a mass of interconnected food chains. By using
the food web as a visual resource, discuss with the pupils what might happen if one of the living
things is removed from the habitat. E.g if too many trout were taken from the river the otter would
lose its food supply while many invertebrates would lose their main predator. If the freshwater shrimp
was removed from the habitat then the detritus (dead plants and animals) on the river bed would not
be broken down and its energy released back into the system. Highlight the importance of this role in
the food web. Once plants and animals die, there needs to be organisms that feed on them in order
to release the energy contained in them so that there is a continual recycling of energy in the food
web. Again (as in Key question 10) , highlight the importance of green plants supporting the whole
food web. It is only plants that can convert the sun’s energy into food and the loss of plants from the
river habitat would quickly impact upon the whole river food web.
11
11a
Food web munchers
Below is a list of some of the plants and animals found in the rivers and
streams of the River Tweed and its tributaries. See if you can use this
information to produce a food web to show some of the feeding relationships in
the river. You will need to draw arrows showing the transfer of energy from the
producers to the consumers. All the things in bold type must be included in your
sunlight
the main source of energy for life on earth
algae
use sunlight energy to produce their own food for life
plants
use sunlight energy to produce their own food for life
detritus
detritus is dead plants and animal that have fallen to the bottom of the river. Some
animals eat this detritus and it is an important source of energy. To keep your food
web simple, think of detritus as coming direct from sunlight energy
Eats
freshwater limpet
algae
mayfly nymph
algae
freshwater shrimp
caseless caddis
fly larvae
water beetle
leech
stonefly nymph
trout
dipper
detritus
mayfly nymphs and freshwater shrimp
plants
freshwater limpets
caseless caddis fly larvae and mayfly nymphs
leeches, mayfly nymphs, freshwater shrimp, caseless caddis fly larvae,
water beetles and stonefly nymphs
mayfly nymphs, freshwater shrimp and caseless caddis fly larvae
otter
trout
heron
trout
River food web (worked example)
1.
2.
3.
11c