Written by Chrissy Wickes
John Marris and James Russell are scientists that have completed several research trips to the Antipodes Islands. They have found unique species of invertebrates as well as clear evidence that mice are having a significant impact on the invertebrate species on the 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. “Comparison between the invertebrate faunas of Antipodes Island and mouse-free Bollons Island indicate that mice have had a major impact on both the abundance and faunal composition of the Antipodes Island invertebrates… The extinction of two species [a ground beetle, Loxomerus n. sp. and an, as yet, uncollected species of weta] on Antipodes Island may be due to mouse predation… Antipodes and Bollons Islands are apparently similar in age, geology, climate and vegetation. It is, therefore, difficult to explain the differences in the composition and abundance of the beetle fauna by anything other than mouse predation on Antipodes Island.” (Marris 2000).
The presence of mice on the main Antipodes Island may explain the apparent absence of large ground-dwelling invertebrates, which are otherwise found on other pest-free [or rodent-free] New Zealand sub-Antarctic islands.
“The most powerful evidence of the impact of mice came from comparison of litter samples between the main Antipodes and the mouse-free Archway Island. Scientists have only ever landed a handful of times on this treacherous offshore Island, and only stayed for 45 minutes. The mouse-free island’s invertebrate was dominated by large amphipods and Collembola (springtails) as well as unique species of other orders such as Coleoptera (beetles) which were not found on the main island.” said James.
A feature of the Antipodes invertebrate fauna 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, and feathers and detritus provide food and habitat for insects.
Marris (2000) found 25 beetle (Coleoptera) species on the Antipodes of which 36% were endemic to the islands. A total of 150 invertebrate species and 20 arachnids were recorded, of which nine species were new to science and 31 were newly recorded from the islands.
While we are obtaining evidence of the detrimental impact of mice on the diversity and abundance of invertebrates on Antipodes Island, we still do not have a clear understanding of the flow-on impacts of these changes 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 including Marion and Gough Islands (Angel & Cooper 2006). These affects derive from the role that the majority of invertebrates play on Subantarctic islands as decomposer species (Vernon et al 1998), releasing organic nutrients held in peat and litter layers by mineralisation (Smith &Steenkamp 1990, 1992, Vernon et al 1998).
See more photos of Antipode invertebrate species: http://species.wikimedia.org/wiki/Category:Antipodes_Islands_nonmarine_fauna
Angel A & Copper J (2006). A Review of the Impacts of Introduced Rodents on the Islands of Tristan da Cunha and Gough. RSPB Research Report No. 17. Royal Society for the Protection of Birds, Sandy, United Kingdom.
Marris J WM (2000). The beetle (Coleoptera) fauna of the Antipodes Islands, with comments on the impact of mice; and an annotated checklist of the insect and arachnid fauna. J Roy Soc NZ 30:169-195
Russell, James, C. (2012). Spatio-temporal patterns of introduced mice and invertebrates on Antipodes Island. Polar Biology, Springer.
Smith V R & Steenkamp M (1990). Climatic change and its ecological implications at a sub Antarctic
Island. Oecologia 85:14-24.
Smith V R & Steenkamp M (1992). Soil macrofauna and nitrogen on a sub Antarctic island. Oecologia
Vernon P, Vannier G & Trehen P (1998). A comparative approach to the entomological diversity of
Polar regions. Acta Oecologica 19:303-308.