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© Boardworks Ltd 20111 of 23
Interdependence
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Competition for resources
All living things compete for natural resources when there is
not enough to go around. They compete in order to survive
and reproduce.
Plants compete for space, light, minerals
and water.
Animals compete for food, water, mates,
territory or shelter.
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Competition in the forest
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Competition on the shoreline
Connell (1961) examined factors that influenced the survival,
distribution, and reproduction of two barnacle species on the
coast of Scotland.
What can you
observe about
the barnacle
distribution?
What do you
think might
have caused
this?
high tide
low tide
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Competition in the Petri dish
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Feeding relationships
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An Antarctic food chain
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Predators and prey
A predator is an animal that hunts and kills other animals
for food. The animal that is eaten is the prey.
plant
Lynxes (a type of
wild cat) and
snowshoe hares
live in northern
parts of North
America.
Which of these animals is a predator and which is its prey?
snowshoe hare lynx
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Predator-prey populations
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Prey population changes
The hare population follows a cyclical pattern, where it rises
and falls in a fairly regular cycle. Why is this?
Individual hares must compete for food and mates, and must
also avoid being killed by lynxes, their predators.
The hare population changes due to both the vegetation
growing season and changes in the lynx population.
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Predator population changes
The lynx population also follows a cyclical pattern very similar
to the hare population. Why is this?
The lynx is very dependent on hares for food, so as the hare
population changes so does the lynx population.
This is why the lynx population rises and falls slightly after the
rise and fall of the hare population.
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Predator-prey cycles
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Changes in food webs
Animals like snowshoe hares and lynxes do not live in
isolation: they are part of complex food webs like the
one below.
How will
changes in the
numbers of
the other
organisms in
this web affect
the numbers
of owls or
voles?
bluetit
owl
finch
stoat
vole
plantaphid
ladybird
mothspider
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What is symbiosis?
Some organisms depend on others for their survival.
Symbiosis occurs when two organisms of different species
live together in a very close relationship.
There are different types of symbiosis
depending on how each organism
benefits or not from the relationship.
The two most well-known types are:
mutualism – both species benefit
parasitism – one species benefits
at the expense of the other species.
Which category would pollination by insects fall into?
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Mutualism and parasitism
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Adaptations of a tapeworm
Tapeworms are long, ribbon-like worms that live inside a
host’s gut. How are they adapted to life as a parasite?
long, thin
body gives
large surface
areas for
absorbing
food
body
covered
by mucus
to protect
against
host’s
digestive
juices
no digestive system needed as
food has already been digested
head has
hooks and
suckers to
hold onto
the gut wall
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Mutualism or parasitism?
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Glossary
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Multiple-choice quiz