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Merremia peltata, disturbance ecology, tropical cyclones and Samoa. The biology and ecology of Merremia peltata are not well understood. While some regard the species as an exotic invader of Pacific Island ecosystems (Meyer. 2000). others identify the plant as a native species likely to be harmful to native ecosystems (Whistler, 1995a. 2002) or as either native or ancient Polynesian introduction behaving invasively (Space and Flynn.(2002). In Samoa, this species occurs up to an elevation of around 300 meters (Whistler 1995a). and thus only affects lowland ecosystems. This species increases its distribution and abundance in two ways, either vegetatively. by sprawling into neighboring areas and rooting from its nodes or by seeds, although early research in the Solomons observed a low seed viability rate, and creeping may thus be its primary means of reproduction (Bacon. 1982). M. peltata has apparently been in the Pacific for hundreds of years (Whistler, pers. com.) but has only become invasive in the years following tropical cyclones Ofa (1990) and Val (1991) according to comments from local government officials. Disturbance thus appears to be an ecological contributing factor to this invasion.

The land snails (and semi-terrestrial molluscs) of the four islands that comprise the Pitcairn group are reviewed and the indigenous species illustrated. The strictly terrestrial molluscan faunas from the two atolls (Oeno and Ducie) are poor, like many other atolls in the Paci c. Each supports less than six species with wide geographical ranges. In contrast, the terrestrial molluscan fauna from Henderson Island, an uplifted atoll, is more diverse with at least 16 species belonging to seven families. Over half these taxa appear to be endemic, at least at the level of sub-species. Two species of semi-terrestrial molluscs have also been found on Henderson. Analyses of archaeological deposits in caves near the North Beach have revealed that at least a further six species of land snail formerly occurred on Henderson. The volcanic island of Pitcairn, the only island in the group still inhabited, supports the greatest number of terrestrial molluscs. Twenty-six species of land snail (and one semi-terrestrial pulmonate) were found living there during the recent expedition and a further three taxa were recognized amongst museum material. At least seven of these species are thought to be recent adventives and a further three are likely to have been prehistoric introductions. One Henderson (Georissa hendersoni) and three Pitcairn endemics (Paci cella lica, Sinployea pitcairnensis and Diastole tenuistriata) are formally described as new species. Some of the Pitcairn endemics occur in very restricted areas (less than a hectare) and it is important that measures should be taken to prevent the spread of invasive plants, such as rose-apple, that would threaten their survival.