The life history patterns of Placostylus fibratus and Placostylus
porphyrostomus can be summarised as being species that exhibit slow growth and
reach maturity late, laying high number of eggs per clutch but with high mortality of newborns, and have long life spans and reproductive life. New Caledonian Placostylus
have evolved in the absence of vertebrate predators and their life history reflects this. Agents that selectively destroys the adults (such as human collection, predation by feral pigs) or the juveniles (rodent predation), or any modification of their habitat (destruction, impact of introduced ungulates) therefore threaten these populations.
Core goals for the preservation of the New Caledonian Placostylus should therefore include preservation of remaining habitats, translocations, reintroductions or supplementations with captive-bred snails, eradication or control of introduced predators (by rodent poisoning or fencing areas again feral pigs), control of the introduced African snail which may compete for food and shelter, and sustainable harvest for human consumption. From a conservation management perspective, Stringer et al. (2004) suggest that the recovery of Placostylus populations in New Zealand is likely to take many years if the number of adults is low to start with. Furthermore, Choat and Schiel (1980) argue that the persistence of populations is the result of a pool of long-lived large adults (10 to 30 years) which are better able to survive unfavourable conditions than small juveniles and thus the populations are best regarded as remnants with questionable long-term viability.
Further work is required to enhance knowledge of the life history of New Caledonian Placostylus, and particularly a more exact understanding of causes and rates of mortality of newborn stages is needed. Nevertheless, these first results on the demographic characteristics of New Caledonian Placostylus, are sufficient to serve as the basis for the construction of a demographic model that could be used to predict the effects of predation and harvests on snail dynamics and allow the development of a plan for the sustainable use of the resource and the long-term persistence of populations (Chapter 8).
4.5 Acknowledgements
All the work on Placostylus snails on Isle of Pines reported here was funded by
the Direction de l’Environnement de la Province Sud (DENV) and the Institut
Agronomique Néo- Calédonien (IAC). Work on Placostylus in dry forests was funded by the Programme de Conservation des Forêts Sèches.
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4.7 APPENDIX 1: NUMBER OF LIVE ADULT AND JUVENILE PLACOSTYLUS AND ACHATINA