By Chrissy Wickes, Services Ranger (Biodiversity)
Scientists, John Marris and James Russell, have completed several research trips to the Antipodes Islands.
They have found a number of unique species of invertebrates on the islands, as well as clear evidence that mice are having a significant impact on the invertebrate species on the main Antipodes Island.
Mice have been present for over 100 years on Antipodes Island, the main island in the group, but have not been recorded on any of the smaller offshore islands of the Antipodes.
Comparisons between the invertebrates of the main Antipodes Island and the nearby mouse-free Bollons Island indicate that mice have had a major impact on both the abundance and variety of species of invertebrates on Antipodes Island.
The extinction of two species – a ground beetle and a species of weta – on the main Antipodes Island may be due to mouse predation.
The main Antipodes Island and Bollons Island are similar in age, geology, climate and vegetation, so it’s difficult to explain the differences by anything other than mouse predation.
A unique feature of the Antipodes invertebrates is the high percentage of species that are found around, or are restricted to, the colonies of nesting birds. The guano enriched soil supports host plants, feathers and other waste, which provide food and habitat for insects.
While we’re starting to get good evidence of the harmful effect of mice on the diversity and abundance of invertebrates on the main Antipodes Island, we still do not have a clear understanding of the flow-on impacts on the overall ecosystem of the island.
Mice compete for invertebrate and seed resources from other native land bird species such as Antipodes snipe and pipit.
Their predation on invertebrates also indirectly affects the rate of nutrient cycling, peat production and primary productivity, as observed on other Subantarctic Islands.
Research on the effect of mice in the Antipodes continues.