Subantarctic islands in the spotlight
Subantarctic researchers from around the world met in Hobart in August for a two-day forum on the future of the subantarctic region, its global significance and value.
Among the speakers at The Third International Forum on the Sub-Antarctic were Australian Antarctic Division terrestrial ecologist Dr Dana Bergstrom and modeller Dr Ben Raymond. The pair has recently published qualitative* modelling research in the Journal of Applied Ecology, examining the range of possible outcomes from the current Macquarie Island Pest Eradication Project.
Speaking at the forum, Dr Raymond said the project aims to eradicate rabbits, rats and mice from the island, and that the modelling supports the anticipated positive outcomes from the project, including the recovery of tall tussock vegetation and burrow- and surface-nesting birds.
However, the modelling also highlights some of the risks of the project, including the potential failure to eradicate mice and an increase in the populations of non-native redpolls and starlings, which mostly likely flew to the island from New Zealand and Australia in the early 1900s.
For example, in nearly half of Dr Raymond’s modelling scenarios targeting rabbits, rats and mice simultaneously, mice were not eradicated due to complex interactions with the other pest species. On parts of Macquarie Island the presence of rats is thought to suppress the mouse population, and the eradication of rats would remove this pressure.
This diagram shows the network of interactions between plants and animals on Macquarie Island (prior to the eradication of cats). Red circles indicate introduced pest species, blue circles are native species, the orange circle is the self-introduced alien redpolls and starlings, and the green circles are vegetation. Dashed lines indicate interactions that are not well understood. Lines ending in an arrow indicate a positive influence and those ending in a dot show a negative influence. For example, herbfield has a positive influence on rabbits (as food), while rabbits have a negative influence on herbfield (because of their grazing).These interactions were used to model different eradication scenarios reported in Journal of Applied Ecology.
‘The effect is exacerbated by the difficulty in targeting all individuals of the mouse population. In other island eradications, failure to eradicate mice has been more common than failure to eradicate rats,’ Dr Raymond said.
The research shows, however, that qualitative modelling can be used to identify gaps in ecosystem knowledge, which can then be addressed, and can provide quite robust conclusions about some management actions, without requiring detailed knowledge of the system.
‘Refinements to this model could be made as new data is collected and as the eradication project unfolds,’ Dr Raymond said.
Other speakers at the forum canvassed the subjects of the subantarctic as a unique source of knowledge, as a climate change sentinel, a source of human enrichment, and as an economic and environmental asset. Alien species management and the impact of and responses to extreme events were also discussed. The stories on the following three pages provide a snapshot of the forum presentations.
Corporate Communications, Australian Antarctic Division
*In this context, qualitative modelling focuses on the structure of the ecosystem and general interactions between organisms. It is different from quantitative modelling which uses detailed mathematical descriptions of specific components in the ecosystem.