The following ecological community could become eligible for listing as threatened under the EPBC Act because of this threatening process: Rainforest on Christmas Island, Indian Ocean, which encompasses six broad habitat types (Christmas Island National Park Management Plan 2002).
Terrace rainforest – open, semi-deciduous rainforest on the coastal terraces
Shallow soil rainforest on the higher terraces
Limestone scree slopes and pinnacles
Deeper plateau and terrace soils evergreen forest
Perennially wet areas
About 100 km of rainforest remains on the island, most of which occurs in the National Park, but some occurs on the adjacent vacant crown land. The rainforest is unique and, until Yellow Crazy Ant invasion, was relatively intact. The expansion of Yellow Crazy Ant supercolonies throughout the ecological community was very rapid, having occurred over about 7 years (c. 1995 to 2002). Before the recent abatement programs, Yellow Crazy Ant supercolonies had formed in 24.4% of the island’s rainforest (Orchard et al 2002) with some estimates being as high as 28% by September 2002. Research has shown that in those areas of rainforest where supecolonies occur, the rainforest is rapidly degraded and changes in a number of ways. For example, in these areas more seedlings and species of seedlings are found on the forest floor, and larger infestations of scale insects are also found, resulting in canopy dieback and death of trees (e.g. O’Dowd et al 2003).
The Christmas Island rainforest ecological community is likely to become threatened if the Yellow Crazy Ants abatement plan ceases or is unsuccessful. It has a highly restricted distribution (100 km22) with a demonstrable threat, as do the many endemic taxa that comprise the community. The major changes to the ecosystem that result from this threatening process would lead to major changes in the structure and composition of the fauna and flora of the area such that the currently defined rainforest ecological community would be lost from those areas.
Conclusion to A: Based on the information provided and summarised above, the TSSC consider that the threatening process:
has the potential to cause a native plant, a number of animal species and an ecological community to become threatened.
The threatening process could cause a number of native species and an ecological to become eligible for listing as threatened, and is therefore eligible under this criterion.
B. Could the threatening process cause a listed threatened species or a listed threatened ecological community to become eligible to be listed in another category representing a higher degree of endangerment?
C. Does the threatening process adversely affect 2 or more listed threatened species (other than conservation dependent species) or 2 or more listed threatened ecological communities?
The discussion of Criteria B and C have been combined as the available evidence for both criteria are similar. There are no invertebrate species on Christmas Island presently listed as threatened, and there is no information available on the impact of Yellow Crazy Ants on listed threatened plants.
Impacts on listed threatened mammals
Pipistrellus murrayi (Christmas Island Pipistrelle): This endemic insectivorous bat is listed as endangered under the EPBC Act and was reported by Lumsden et al (1999) to have declined markedly and contracted in its distribution from the mid-1980s to 1998. Reasons for the decline were unclear, but there was concern that that Yellow Crazy Ants may have a role in threatening this species. However, it was considered that there were also likely to be other threatening processes at work, as the decline was occurring in both the areas where Yellow Crazy Ant supercolonies were present and those they were not (Lumsden et al 1999). Since 1998, areas of high or moderate levels of pipistrelle activity, considered to be the stronghold for the species, were either invaded by ant supercolonies or were within a supercolonies’ foraging range (Schulz & Lumsden 2004).
Yellow Crazy Ants may impact directly on the Christmas Island Pipistrelle in a number of ways. These bats roost on tree trunks and in hollows, microhabitats that are heavily used by Yellow Crazy Ants. The bats have been attacked and killed by ants: one individual captured in a trap died as a result of Yellow Crazy Ant attack in 1998 (Lumsden et al 1999). Bats contacted by Yellow Crazy Ants that are not killed directly may be adversely affected by exposure to sprayed formic acid leading to blindness and physiological stress (O’Dowd et al 1999). In areas of Yellow Crazy Ant supercolonies, it is thought that the pipistrelle may be forced to find alternative roosts, if available, and these may offer less protection. Maternity sites of this bat are also considered to be vulnerable. Although no maternity sites for the pipistrelle have been located, they are likely to be situated in the hollows of rainforest canopy trees, a microhabitat also used by Yellow Crazy Ants. Given the small size of the pipistrelle (adults weigh 3-4.5 g with new-born young likely to weigh approximately 1 g) individuals at maternity sites within supercolony areas would be considered at risk. The availability of the invertebrate prey of the Pipistrelle may also have decreased due to the foraging activity of the ants (Schulz & Lumsden 2004).
There are also indirect impacts that may occur as a result of this process. The removal of Red Land Crabs may allow greater penetration into the rainforest of Wolf Snakes, which are thought to have had a major role in the initial decline in pipstrelles, as well as other predators such as feral cats and rats.
Currently, it is not known what impact the Yellow Crazy Ant has on the Christmas Island Pipistrelle. The recovery plan for the Christmas Island Pipistrelle (Schulz & Lumsden 2004) states that it is likely that the Yellow Crazy Ants are compounding the impact of earlier declines and that the continuing spread of the ant would be harmful to the long-term survival of the pipistrelle.
As nearly all of the areas of greatest activity of the pipistrelle have been affected by Yellow Crazy Ants supercolonies, and the pipistrelle appears to use microhabitats that are heavily used by Yellow Crazy Ants, the threatening process is considered to be adversely affecting the Christmas Island Pipistrelle, and it could become eligible to be listed in a category representing a higher degree of endangerment as a result of this process.
Crocidura attenuata trichura (Christmas Island Shrew): In the recovery plan (Schulz 2004) for this nationally endangered entity, Yellow Crazy Ants have been identified as one of the threatening processes. The species was widespread and abundant on Christmas Island at the time of European settlement, occurring in rainforest. It appeared to decline rapidly, with the only records after 1908 being an accidental finding of two single individuals in 1985. The species has not been recorded since this finding despite targeted surveys, and is considered by some to be possibly extinct (Schulz 2004). Yellow Crazy Ant supercolonies have subsequently formed at the site of the 1985 sightings. The shrew was recorded to shelter in holes in rocks and roots of trees, and to forage on small beetles (Andrews 1900).
The direct effects of Yellow Crazy Ants on the shrew are unknown, but it is likely that breeding, shelter and foraging sites would be severely affected. It is also likely the ants would kill young animals in the nest and, possibly, adults in severely affected areas (Schulz 2004). This threatening process is considered to be adversely affecting the Christmas Island Shrew, and it could become eligible to be listed in a category representing a higher degree of endangerment as a result of this process.