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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 Nicole Murnane 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 Nicole Murnane 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 Nicole Murnane 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 Nicole Murnane 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. Nicole Murnane 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? Nicole Murnane Nicole Murnane What did this mean for the petrels? Year Population numbers 1970 2000 1992 1400 What type of data is this? Nicole Murnane 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 Nicole Murnane 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 Nicole Murnane Describe the general trend of this graph: Nicole Murnane