Increasing numbers of rabbits and rodents on Macquarie Island have devastating effects on native fauna, flora, geomorphology, natural landscape values and nutrient recycling systems.
The rabbit exclosure above shows that the vegetation of Macquarie Island
is capable of regenerating with the absence of rabbit grazing in just a few years.
This exclosure contains naturally regenerating Macquarie Island cabbage
In recent years there has been a significant increase in damage to vegetation caused by rabbits on Macquarie Island.
European rabbits, Oryctolagus cuniculus
, favour the grasses and large leafy megaherbs including the Macquarie Island cabbage Stilbocarpa polaris
and the daisy Pleurophyllum hookeri.
These species have no adaptations to cope with grazing.
Vegetation communities are a critical part of the Macquarie Island ecosystem as they protect soil and rocks from weathering, stabilise steep slopes and provide habitat for invertebrates and burrow-nesting seabirds.
Rabbit grazing is changing areas of tall tussock grassland to modified forms of herb-field, thereby affecting the breeding success of all burrowing seabirds that require vegetation cover as part of their breeding habitat.
The loss of vegetation also causes destabilisation and erosion of steep peat-covered slopes, which also impacts on albatross nesting sites. Two landslides in 2006, at least partially caused by rabbit grazing, were responsible for the deaths of penguins and damage to visitor boardwalks on the island.
Rodents are also having a significant impact on the island, particularly ship rats Rattus rattus
which are omnivorous and will prey on chicks and eggs of burrow-nesting petrels.
Ship rats and house mice Mus musculus
also impede plant seedling recruitment and forage on invertebrates.
Ship rats are identified as an ongoing threat to at least nine bird species that breed on Macquarie Island.
Pests on Islands
Wildlife on islands, particularly those on islands such as Macquarie which are isolated in a geographical and evolutionary sense, are extremely vulnerable to introduced species.
Plants and animals in such places have evolved in isolation and are adapted to unique local conditions; many do not have the ability to resist the invasive characteristics of alien introductions. For example, the tendency of rails to evolve flightless forms on islands has led to the disproportionate number of extinctions in that family as a result of predation by introduced species. For example, the Macquarie Island rail is now extinct.
Introduced species often have no natural predators or are able to fill a vacant niche. Rabbits have been extremely successful on Macquarie Island due to the lack of competitors for food resources.
Experts working on introduced species agree that islands (and other geographically and evolutionary isolated places) face different threats to biodiversity compared to continental situations. They are more vulnerable to invasions and more likely to suffer catastrophic loss of biodiversity as a result of invasions. Fortunately such places are also more likely to respond well to successful pest eradication campaigns.