Threats
The single known population of Newcomb’s tree snail occurs on private land that is currently zoned and managed as conservation land. However, the habitat on the ridge where 8 of the 9 living Newcomb’s snail were found is badly degraded by the invasion of nonnative invasive plants. Many of the small ohia lehua trees that are the main host tree for this tree snail have died as well as two trees that had marked Newcomb’s tree snails in them. The native uluhe fern is being replaced by Rubus sp. (blackberry), Melinis minutiflora (molasses grass), Tibouchina sp., and invasive grasses.
The collections for scientific as well as recreational purposes in the 18th to early 20th centuries of Newcomb’s tree snails do not seem to be nearly as extensive, probably due to the fact that the shell of these snails lacks the luster and diversity of color and pattern that characterize Achatinella and Partulina.
Diseases are not known to have contributed to declines in the Hawaiian tree snail fauna. Predation, however, has had severe impacts on the tree snail fauna of Hawaii and other Pacific islands. The black rat Rattus rattus appears to be a major threat to the Newcomb’s tree snail on Maui. During the first year of the mark-recapture study initiated in 1996 for Newcomb’s tree snails, evidence of rat predation on other tree snail species within the study area was documented. No direct evidence of rat predation on Newcomb’s tree snails were found, though researchers theorized that no Newcomb’s tree snail shells were found because of their fragility, small size, and brown coloration, which would make it much more difficult to find in the leaf litter in comparison to other predated snail shells. Norway rat Rattus norvegicus and Polynesian rat Rattus exulans are the major introduced predators on extant populations of Hawaiian tree snails.
The rosy carnivore snail is a voracious predator on terrestrial and arboreal snails and Hadfield (2007) reported finding several live rosy carnivore snails within the habitat of the remaining Newcomb’s tree snails.
Other possible predators of Newcomb’s tree snails include an introduced terrestrial flatworm Platydemus manokwari and the introduced terrestrial snail Oxychilus alliarius, which have both been reported to feed on snails. Platydemus manokwari probably lives also on Maui. Hadfield (2007) reported finding many shells of Oxychilus alliarius within the habitat of the remaining Newcomb’s tree snails.
Read more about this topic: Newcombia Cumingi
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