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Human impact on
ecosystems
Introduction of exotic species
Nicole Murnane
Cabbage Tree Island
Is located off the coast of NSW
 tropical rainforest ecosystem
 The island is home to many bird
species, including the endangered
Gould’s petrel – the rarest of
Australia’s endemic sea birds

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Gould’s Petrel
Rare sea bird, native to
Australia
 Spend most of their life at sea
 Each year, after they reach about six
years of age, the birds return to shore
to breed (October to May)
 They nest in cavities among rocky
debris or under fallen palm fronds

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Rabbits on Cabbage Tree
Island
The introduction of rabbits
onto the island occurred in 1906
 Since then, rabbits have multiplied
rapidly. Why?
 The browsing of the large rabbit
numbers placed significant pressure
plant growth on the island

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Rabbits on Cabbage Tree
Island
The rabbits totally destroyed the herb
and shrub layers
 They also ate seedlings that would
have eventually become part of the
upper canopy of the tropical rainforest
 Over time, the loss of the understorey
and the lack of replacement canopy
trees changed the closed forest to an
open forest

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Breeding like rabbits!

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Rabbits have a high reproductive rate:
one female can produce up to 30 kittens
per year
In their natural habitats in Europe, rabbit
populations remain constant because of
winter food shortages and the presence
of predators, parasites and competitors.
However in Australia the rabbits did not
face they same problems and their
population numbers exploded.
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A changed ecosystem….
Loss of the trees and shrubs exposed
the petrels to predation by pied
currawongs and ravens
 The loss of the understorey also
exposed the petrels to the fruits of the
native bird-lime tree – instead of being
trapped by the shrubs, the fruit falls to
the ground and the petrels become
entangled. Why?

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What did this mean for the
petrels?
Year
Population numbers
1970
2000
1992
1400
What type of data is this?
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Measures to restore the
balance
In 1993, the NSW National Parks and
Wildlife Service began a management
program on Cabbage Tree Island:
 Culling currawongs and ravens
 Eradicating bird-lime trees from the
petrel’s breeding sites
 Exterminating rabbits
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At last, the rabbits go!

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The program used a combination of
myxomatosis virus, rabbit calicivirus and
poisoning with baits to eradicate the
rabbits from the island
Extermination was complete in just 8
weeks
Over time, the understorey and canopy
have recovered and the ecosystem has
returned to a closed forest
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Describe the general trend of this graph:
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