Year 11 Pre-Diploma Biology
ECOLOGY – FOOD WEBS AND CHAINS
FOOD WEBS & FOOD CHAINS should by now be a well understood concept so, try this difficult
problem. Convert the following written information into a diagrammatic form – a food web. You
may have to research a little to find out what some of the organisms are, although their actual
names are not so important.
The following relationships may be observed on many rocky sea shores, some when the tide is
in (high tide) and some when the tide is out (low tide):
(i)
Limpets (molluscs) grazing on diatoms (small algae), which are attached to rocks
(ii)
dog-whelks (snails) eating barnacles (crustaceans) and mussels (molluscs)
(iii)
crabs consuming dead mussels in cracks in the rocks
(iv)
barnacles feeding on zooplankton (animal plankton, often one celled organisms or
tiny larvae of crustaceans, etc.)
(v)
mussels feeding on phytoplankton (plant plankton – single celled algae, etc.)
(vi)
periwinkles (snails) feeding on diatoms attached to seaweeds
(vii)
sea-gulls (scavenging sea birds) feeding on dead crabs
(viii)
turnstones (a wading bird) feeding on dog-whelks, limpets and periwinkles, which they
kill.
a)
(i)
Which of the organisms above are herbivores
Mussel, Limpet, periwinkle and dog-whelk are secondary consumers
(ii)
Which are primary consumers?
Zooplankton, diatoms and phytoplankton are primary consumers
(iii)
which are autotrophs
Zooplankton, diatoms and phytoplankton are primary consumers
(iv)
which are secondary consumers
Mussel, Limpet, periwinkle and dog-whelk are secondary consumers
(v)
which are tertiary consumers
Turnstone and crab
(vi)
which are detritivores
Scavengers
(vii)
Which are heterotrophs?
Sea-gulls
b)
Construct two complete food chains from the descriptions given above. Of course,
each food chain does not need to include all the organisms listed in (i) to (viii) above.
First food web
Sea -gull
Crab
Mussel
Phytoplankton
Second food web
Turnstone
Periwinkle
Dog-whelk
Barnacle
Diatoms
Zooplankton
c)
Construct a whole food web for this rocky shore community.
Sea gull
Crab
Mussel
Turnstone
Dog-whelk
Periwinkle
Barnacle
Diatoms
Zooplankton
Limpet