The demographics of destruction: isolated populations of arboreal snails and sustained predation by rats on the island of Moloka’i 1982–2006

摘要

Populations of Partulina redfieldi, an achatinelline tree snail studied in four isolated trees, grew 100–900% between 1983 and 1995. Beginning in 1995, populations declined by 85%, and shells of rat-killed snails accumulated beneath the trees. While rat-marked shells were always present in the study area, numbers increased significantly. Despite a rat-abatement program begun in 1995, the snails continued to disappear, which we conclude was due to continued rat migration into the study area, despite baiting, and a switch in rat-food preference toward the snails. In neighboring forest where tree canopies are more continuous, snail density is lower and rat predation is not apparent. Captive-bred snails were successfully introduced to a small unoccupied tree in the same area in 1989, and this population suffered the same fate as the natural snail populations. Since 2000, P. redfieldi populations have remained low and rat predation continues.