National Recovery Plan for the Christmas Island Spleenwort Asplenium listeri
C.2.4 Exotic faunaC.2.4 Exotic fauna
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C.2.4 Exotic fauna
There are no records indicating any specific threats from the activity of exotic fauna.
The species occasioning most concern on the island in recent times is yellow crazy ant (Anoplolepsis gracilipes), which was introduced accidentally between 1915 and 1934. It has recently undergone a population explosion and the ants have formed multi-queened ‘supercolonies’. This has had a marked impact on other terrestrial fauna such as land crabs and in turn has changed the vegetation profile in some forest types. Although Asplenium listeri may be vulnerable to episodic changes in canopy density or encroachment by other vegetation (Holmes & Holmes 2002), the effects brought about by the yellow crazy ant are not considered likely to affect the areas associated with Asplenium listeri (Claussen pers. comm.).
Of greater potential impact may be the giant African snail (Achatina fulica) which feeds on a wide variety of plants but may be expected to take refuge in moist locations, including those favoured by ferns. It is not known whether this species has had, or is likely to have, any impact on Asplenium listeri. Although the presence of land crabs appears to restrict the distribution of the snail, this controlling effect may be compromised by reduced crab populations brought about by the yellow crazy ant infestation (CofA 2002).
Crazy ant populations are responding to a program of aerial baiting, however the potential for increased spread of the snail may be inferred, because there may be a gap of many years before land crabs recover to a level sufficient to control snail populations. Parks Australia monitor presence/absence of the snail during surveys for crazy ant populations, and these data could be related to the distribution of Asplenium listeri to assess any interactions (Jeffery pers. comm.).
Also of potential concern is an exotic millipede which feeds on vegetable matter and occurs in very high densities in certain areas (Sewell pers. comm.). No additional information was located on this.