Human impact on ecosystems

Introduction of exotic species

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Cabbage Tree Island

Is located off the coast of NSWtropical rainforest ecosystemThe 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!

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!

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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