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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