Status and ecological importance of rainforest land snails on the island of Hawaii

The native Hawaiian land snail fauna used to be extremely diverse (over 750 species) and exhibited extremely high endemism (over 99%), but the majority of these unique species are now extinct and are being replaced by a small number of widespread alien species. Unfortunately, it is difficult for biodiversity managers to make informed decisions concerning the preservation of biodiversity and ecosystem function because patterns of mollusc diversity and distribution are largely unknown, as are the influences of these species on key ecosystem processes. This dissertation addresses the diversity and ecology of terrestrial molluscs on the eastern (windward) side of the island of Hawaii and explores the roles of the abundant species. Following an introductory chapter, Chapter 2 documents the elevational distribution of native and alien molluscs from tropical and temperate regions. Since alien species from temperate regions had wide elevational distributions and were dominant components of the mollusc fauna at high elevations, which on many tropical islands are the last refuges of the native species, preventing the introduction of temperate species should be a conservation priority. Chapter 3 addresses the feeding ecology of two introduced predatory snails. The results have unfortunate conservation ramifications since they indicate that both Euglandina rosea and Oxychilus alliarius are generalist snail predators feeding preferentially on the smallest snails (many native Hawaiian snails are very small), and that they rarely eat slugs (no native slugs in Hawaii). Chapter 4 evaluates the genetic diversity of the rainforest Succineidae using a molecular approach. Phylogenetic analysis of mitochondrial and nuclear DNA sequences indicates the presence of multiple cryptic species in sympatry, which implies that previous ecological studies and conservation assessments of Hawaiian succineids are confounded. Chapter 5 examines the role of molluscs in important ecosystem processes. The results indicate that molluscs and other macro-invertebrates influence litter decomposition and nutrient cycling. A concluding chapter focuses on the conservation implications of the findings and suggests that management practices that aim to preserve both biodiversity and ecosystem function will have to weigh both the negative effects of alien mollusc species on native diversity against their potential positive effects on ecosystem processes.