Extant populations of endemic partulids on Tahiti, French Polynesia

Abstract

The current distribution of endemic partulid snails on Tahiti in French Polynesia reflects the danger of ignoring expert advice and introducing an alien species into a fragile island ecosystem. The endemic tree-snail fauna of the island now faces extinction. Although the extinction of the native species of Partula (Partulidae; Polynesian tree snails) on Moorea in French Polynesia is well known in the world of conservation biology, losses on other Pacific islands are less well described. This paper presents an update on the status of partulid snail populations on Tahiti in the light of fieldwork undertaken between 1995 and 1997. Native snails still exist in good numbers in two areas, at opposite ends of the island. In other areas, sightings of single or a few individuals indicate remnant populations now on the edge of extinction. Efforts to protect these populations and others in French Polynesia are being planned in collaboration with local government authorities.

Predator, prey and pathogen interactions in introduced snail populations

“…In all model scenarios E. rosea populations persist following declines in prey; where prey are limited to A. fulica, populations may cycle between 50-210/ha, levels at which they may be difficult to detect and may be vulnerable to local stochastic extinctions, as has been reported from some field sites (Coote et al, 1999(Coote et al, , 2000. Although this possibility of stochastic extinction may allow local recovery of prey species it does not offer good long-term survival prospects for the remaining populations of Partulidae.…”

“…Samoana spp. were originally believed to follow this pattern but recent observations suggest that small populations persist in some areas (Coote et al, 1999(Coote et al, , 2000.…”

“…The exception to this pattern are Samoana spp., which are predicted to decline by 75% within 3 years of E. rosea invasion before recovering to 41% of the original population. Field data from Polynesia support these predictions, with the extinction of Partula spp., Trochomorpha typus and Diastole conula within a few years of E. rosea invasion (Clarke et al, 1984;Murray et al, 1988;Cowie, 1992;Gerlach, 1994;Coote et al, 1999Coote et al, , 2000. Samoana spp.…”

“…Published data from Mauritius, Réunion, New Caledonia and French Polynesia suggest that populations of A. fulica and E. rosea are stable, with the exception of Raiatea (French Polynesia) (Pearce-Kelly & Clarke, 1992;Coote et al, 1999). On this island E. rosea was spreading across the island during the period of study, reaching complete coverage of all habitats in 1993 (Pearce-Kelly et al, 1994).…”

“…Throughout much of the introduced range of A. fulica the carnivorous snail Euglandina rosea has been introduced in biological control programmes (Mead, 1961;Tillier & Clarke, 1983;Murray et al, 1988). The failure of these programmes and the devastating effect that E. rosea has had on many indigenous, non-pest species is well known (Tillier & Clarke, 1983;Clarke, Murray & Johnson, 1984;Hadfield, 1986;Murray et al, 1988;Cowie, 1992; Pearce-Kelly, Clarke & Mace, 1994;Coote et al, 1999Coote et al, , 2000. Research into the ecology of E. rosea has elucidated various aspects of the feeding and reproductive biology and the basics of population dynamics in the species (Cooke, 1983(Cooke, , 1985a(Cooke, ,b,c, 1989aGerlach, 1994Gerlach, , 1999.…”