Island fauna are particularly vulnerable to new threats. Not only do they have a very limited population size and distribution to begin with, they can display extreme naïveté to new predators, due to a lack, or at least reduced diversity, of native predators on the island.
The Kangaroo Island Dunnart (Sminthopsis aitkeni) is an example of a critically endangered island mammal. It was previously thought to be a population of the Common Dunnart (Sminthopsis murina), but morphological and genetic studies revealed it to be a distinct species. The small (less than 25g) insectivorous marsupial has only been recorded from Kangaroo Island, although genetic studies have revealed it is very closely related with the Grey-bellied Dunnart (Sminthopsis griseoventer) from mainland South Australia and Western Australia.
The Kangaroo Island Dunnart differs from other closely related dunnart species in its dark sooty colouration. Unlike some other species of dunnarts, it does not store fat in its tail. It mainly feeds on spiders and ants, with the occasional beetle and scorpion.
The Kangaroo Island Dunnart was listed as Critically Endangered in 2008, as all individuals since 1990 come from sites within the Flinders Chase National Park and Ravine des Casoars Wilderness Protection Area on the western end of Kangaroo Island. Despite extensive trapping since 1990, including over 17,800 pitfall traps nights and 20,400 Elliott trap nights, the dunnart is only known from 35 records and 6 trapping sites. Twelve of the 28 captures since 1990 come from one site alone. Extensive fieldwork has failed to locate the dunnart elsewhere on the island.
Loss of habitat of habitat for agriculture appears to have caused the decline of the dunnart from throughout the island to the western edge. Nearly 50% of the natural vegetation of Kangaroo Island has been cleared.
The extremely small population with a limited distribution makes the dunnart susceptible to catastrophic events such as wildfire. Dieback of vegetation caused by the Phytophthora cinnamoni fungus is apparent on Kangaroo Island, and could expose the dunnarts to predation. Foxes are absent from Kangaroo Island, but feral cats are widespread and could be a potential impact on the dunnarts.
With such small populations, the main strategy is to protect the dunnarts from wildfires. This requires more research on the best fire management practises. Establishment of further populations could alleviate any future pressure from catastrophic events. Cat control could also be beneficial; especially predation could have a large effect on a small population.
The limited information on population trends suggests more research is required on this species. This requires more intensive monitoring, and possibly adaptive management.
The Kangaroo Island Dunnart is a highly restricted species with a small population. As such it is highly vulnerable to catastrophic effects. Without adequate fire control, and establishment on more populations, the Kangaroo Island Dunnart may join the list of Australia’s extinct mammal species.
Images supplied by Jody Gates at the South Australian Department of Environment, Water, and Natural Resources.
The Conversation is running a series on Australian endangered species. See it here.