Diversity and current conservation status of ...

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Pacific Conservation Biology http://dx.doi.org/10.1071/PC14929

Diversity and current conservation status of Melanesian– New Zealand placostyline land snails (Gastropoda : Bothriembryontidae), with discussion of conservation imperatives, priorities and methodology issues Gary M. Barker A,D, Gilianne Brodie B, Lia Bogitini B and Helen Pippard C A

Landcare Research, Private Bag 3127, Hamilton 3240, New Zealand. School of Biological and Chemical Sciences, University of the South Pacific, Private Bag, Suva, Fiji. C IUCN Oceania Regional Office, 5 Ma’afu Street, Suva, Fiji. D Corresponding author. Email: [email protected] B

Abstract. We review the diversity and conservation status of Placostylinae, land snails endemic to the western Pacific. Their narrow-range endemism, large size and associated vulnerability, consumptive exploitation by people, and habitat loss and degradation (inclusive of invasive predators) threaten their survival. There has been considerable attention from conservation biologists in New Caledonia, Lord Howe Island and New Zealand aimed at species recovery. Nonetheless, only on uninhabited, pest-free islands do these native snails persist in high numbers, and these remaining ‘sanctuaries’ are dependent on biosecurity vigilance. For other populations in New Caledonia, Lord Howe Island and New Zealand, the benefits of control of invasive mesopredators have been demonstrated, but it remains unclear if long-term persistence of Placostylinae can be achieved in degraded landscapes that continue to be subject to anthropogenic pressures. For species in Fiji, Vanuatu, and the Solomon Islands – the centre of Placostylinae diversity – their conservation status is not known with any certainty due to lack of basic data on range and population trends. Recent IUCN Red List assessments indicate a high level of extinction risk among Fijian species due to narrow geographic range coupled with decline in habitat extent and quality. Further inventory and ecological work is urgently needed in the Solomon Islands and Vanuatu to enable assessment of extinction risk and identify threatening processes. We identify four priority areas for advancing the conservation of Placostylinae, especially in Melanesia, and discuss the most pressing methodological issues. Molecular phylogenetic analyses are needed to provide an evolutionary framework for taxonomic revision and to underpin development of both conservation policy and species recovery plans. Additional keywords: conservation imperatives, conservation management, extinction risk, forest disturbance, invasive species, population decline, recovery plans, threatening processes. Received 5 February 2015, accepted 17 November 2015, published online 19 February 2016

Introduction Bothriembryontidae Iredale, 1937 (Syn. Placostylidae Pilsbry, 1946) is a Gondwanan element within the superfamily Orthalicoidea that spans three continents, namely South America, Africa and Australia, plus islands of the western Pacific (New Caledonia and Loyalty Islands, Solomon Islands – inclusive of Santa Cruz Islands, Vanuatu, Fiji exclusive of the Lau Archipelago, Lord Howe Island, and northern New Zealand) (Climo 1975; Barker 2005; Herbert and Mitchell 2009; Neubert et al. 2009; Breure et al. 2010; Breure and Romero 2012; Cuezzo et al. 2013; Araya and Catalań 2014). The Melanesian–New Zealand members are presently treated as a distinct subfamily, Placostylinae. Many Bothriembryontidae, including members of Placostylinae, are recognised as threatened by anthropogenic disturbances that include habitat loss and fragmentation, habitat Journal compilation Ó CSIRO 2016

degradation by fire and grazing, predation by invasive species, and harvesting for human consumption. Several species of Placostylinae have long been under active conservation management in New Zealand and on Lord Howe Island, and more recently in New Caledonia, with the objective of halting their decline. In the face of increasing pressures from land-use change and invasive species, there is increasing concern about the status of Placostylinae also in the Solomon Islands, Vanuatu and Fiji, but conservation actions there are constrained by lack of data to inform policy, action plans and operational activities. In this paper we review what is presently known about the diversity, biogeography and conservation status of Placostylinae, with the primary focus on synthesis of the information relevant to formulation and implementation of conservation action plans. www.publish.csiro.au/journals/pcb

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Patterns of diversity The molecular phylogenetic analyses of Breure et al. (2010) and Breure and Romero (2012) support Bothriembryontidae as monophyletic, with a pre-Cretaceous origin in South America. The dispersion across the three Gondwanan continents of South America, Africa and Australia, plus the Gondwanan-fragment islands of New Zealand and New Caledonia, point to a role of vicariance in the diversification of this group. Nonetheless, the evolutionary history of the Melanesian–New Zealand Placostylinae is currently poorly understood. In discussing the distribution of the snails now classified as Placostylinae, Hedley (1892, 1898; 1899) postulated the existence of a former Melanesian continent [which he called the Melanesian Plateau] embracing the area from New Guinea to Fiji and New Zealand. This area of land, even if not a continuous mass, was postulated to have been sufficient to allow essentially dry land connections and thus passage of the placostylines. This is more or less consistent with modern geological understanding of the ancient island arc systems of Melanesia and those associated with Lord Howe Rise and Norfolk Ridge (e.g. Crook and Belbin 1978; Coulson 1985; Coleman 1997; Hall 2001; Crawford et al. 2003). Hedley (1892) initially suggested an Indonesian derivation for these snails but, later recognising the affinities with the South American Bulimulidae, Hedley (1899) proposed an Antarctic migration in Mesozoic or Palaeozoic times. This view was adopted by Pilsbry (1900, 1911) and several other authors. Sixteen genus-group names have been recognised in Placostylinae. Haas (1935) restricted Placostylus Beck, 1837 to New Caledonia. Ponder et al. (2003) observed that New Zealand, Lord Howe and New Caledonian taxa, with their large, solid shells, are more similar to one another than to the other taxa further north, as noted by Hedley (1892) and Pilsbry (1900), and suggested a probable phylogenetic unity. Based on published anatomical information (e.g. Pilsbry 1900, 1901–02; Clapp 1923; Rensch and Rensch 1935; Kondo 1948; Solem 1959; Turner and Clench 1972; Breure and Schouten 1985) and a rather limited new anatomical survey of Placostylinae, Neubert et al. (2009) considered Placostylus s. str. to be restricted to New Zealand, Lord Howe and New Caledonia. They suggested that species-group taxa for the remaining Melanesian island groups be referred to the available genus-group names, pending a comprehensive investigation of Placostylinae as a whole. Trewick et al. (2009) accepted the Neubert et al. (2009) interpretation of Placostylus s. str. Their molecular phylogenetic analyses (Trewick et al. 2009: 431) were purported to indicate the New Zealand and Lord Howe Placostylus as basal to the monophyletic New Caledonian radiation, suggesting a ‘northward directionality in dispersal of Placostylus among these islands’. While not discussed by Trewick et al. (2009), this result is consistent with origins of the Placostylinae by vicariance during the Cretaceous split of pro-New Zealandia from Gondwana, but independent of a similar but more northern Cretaceous split of pro-New Caledonia. However, these conclusions are weakly supported, with incongruence among phylogenetic trees, and based on a single mitochondrial gene. Furthermore, these types of molecular analyses have yet to include Placostylinae of the Solomon Islands, Vanuatu and Fiji.

G. M. Barker et al.

It is clear that the Placostylinae is an endemic south-west Pacific radiation associated with the eastern margin of the Australian Plate and, as observed by Brook and Laurenson (1992: 158), ‘given a presumed limited ability to disperse across ocean basins, suggests that it had an eastern Gondwana origin’. Nonetheless, Solem (1959: 327) argued for a northern origin of Placostylinae, with ‘an original movement from ‘Papua’ to New Zealand through the New Caledonian–New Hebrides [=Vanuatu] region, a second movement into New Caledonia, and a third to the Solomons and Fijis [sic?] y’. Solem (1959: 130, fig. 5) concluded that the Vanuatu, New Zealand and Lord Howe Island taxa were more closely related than any of these were to those of New Caledonia, Solomon Islands or Fiji. Recent morphological (Neubert et al. 2009) and molecular (Trewick et al. 2009) analyses indicate genetic structure within New Caledonian Placostylus s. str. that is not currently formally recognised in supraspecific taxonomy. By contrast, the phylogenetic structuring within the more southern Placostylus s. str. has long been formalised, with the description of subgenera – Basileostylus Haas 1935, established for the Three Kings Islands, New Zealand, P. bollonsi Suter, 1908, and Maoristylus Haas, 1935 erected for northern New Zealand Placostylus hongii (Lesson, 1830) and includes P. ambagiosus Suter, 1906 from the same region, and Placostylus bivaricosus (Gaskoin, 1855) of Lord Howe Island. Recognition of subgenera Basileostylus and Maoristylus is supported by recent molecular phylogenetic analyses (Ponder et al. 2003; Trewick et al. 2009). As suggested by Neubert et al. (2009), the remaining genusgroup taxa in Placostylinae are here treated as genera pending a revision. Of these genus-group taxa (Table 1), five are known from the Solomon Islands (Aspastus Albers, 1850; Eumecostylus Albers, 1860 (syn. Proaspastus Clench 1941); Placocharis Pilsbry, 1900; Santacharis Iredale, 1927; Malaitella Clench, 1941), three from Vanuatu (Diplomorpha Ancey, 1884; Poecilocharis Kobelt, 1891; Quiros Solem, 1959), two from Fiji (Callistocharis Pilsbry, 1900; Euplacostylus Crosse, 1875), and one from New Caledonia (Leucocharis Pilsbry, 1900). It should be noted that these genus-group names have often been used in the sense of subgenera of Placostylus, even in the face of mounting evidence that Placostylus s. str. is restricted to New Caledonia, Lord Howe and New Zealand, as outlined above. There has yet to be any critical assessment of interrelationships among placostyline genus-group taxa via molecular and/or morphological phylogenetic analyses and there continues to be much instability in their taxonomy. The current classification of Placostylinae indicates a total of 70 species-level taxa (Table 1), but possibly others await discovery. The checklist in Table 1 is compiled principally from Pilsbry (1900, 1901–02), Clench (1941), Franc (1957), Solem (1959, 1961), Zilch (1972), Breure (1975, 1976), Powell (1979), Richardson (1995), Neubert and Janssen (2004), Ko¨hler (2007), Neubert et al. (2009); Barker and Bouchet (2010), Delsaerdt (2010), Breure (2011) and Breure and Ablett (2014) (see these references for taxon names reduced to junior synonymies). The centre of diversity is the Melanesian region, especially the Solomon Islands with 35 species. Despite low infraspecific genetic diversity (Ponder et al. 2003; Trewick et al. 2009; Buckley et al. 2011), there is often considerable geographic structure within placostyline species,

Diversity and conservation status of Placostylinae


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Table 1. Checklist of genus-group and species-group taxa in Placostylinae, with information on type species of genus-group taxa and distributions (island occupancies) Species

Distribution (islands)

Genus Aspastus Albers, 1850 (Solomon Islands) A. albolabris (Brazier, 1895) San Cristobal [Makira]; Santa Anna [Owaraha] A. miltocheilus (Reeve, 1848)A Bio; San Cristobal; Santa Anna; Savo; Ugi; Ulaua A. sellersi (Cox, 1871) Guadacanal Genus Callistocharis Pilsbry, 1900 (Fiji) C. elobatus (Gould, 1846) Vanua Levu C. fulguratus (Jay, 1842) Viti Levu, Vanua Levu, Ovalau, Mbenga C. garretti Pilsbry, 1900 From unspecified Fijian locality – probably Viti Levu C. graeffei Crosse, 1875 Viti Levu C. guanensis (Garrett, 1872) Ngau C. hoyti (Garrett, 1872) Vanua Levu C. malleatus (Jay, 1842)A Viti Levu, Ovalau C. morosus (Gould, 1846) Viti Levu, Ovalau, Kandavu, Vanua Levu, Taveuni, Rambi, Koro, Gomea, Lanthala C. ochrostoma (Garrett, 1872) Vanua Levu, Taveuni, Rambi C. subroseus Fulton, 1915 From unspecified Fijian locality Genus Diplomorpha Ancey, 1884 s. str. (Vanuatu) D. brazieri Hartman, 1889 Espiritu Santo, Aore D. coxi (Pease, 1871) From unspecified Vanuatu locality – probably Aneiteum D. delautouri (Hartman, 1886) Aore; Omba; Espiritu Santo D. layardi Ancey, 1884A Vate D. peasei (Cox, 1871) Aore Subgenus Quiros Solem, 1959 (Vanuatu) D. bernieri (Hartman, 1890)A Espiritu Santo Genus Eumecostylus Martens, in Albers 1860 (Solomon Islands) E. almiranta Clench, 1941 New Georgia; Malaita E. calus (Smith, 1891) Malaita E. cleryi (Petit, 1850)A San Christobal E. cylindricus (Fulton, 1903) Guadalcanal; possibly also Ysabel E. foxi Clench, 1941 San Christobal E. fraterculus (Rensch, 1934) Guadalcanal E. gallegoi Clench, 1941 San Christobal E. gardneri Delsaerdt, 2010 Guadalcanal E. hargravesi (Cox, 1871) Malaita; possibly also Treasury E. kirakiraensis (Rensch, 1934) San Christobal E. phenax Clapp, 1923 San Christobal E. sanchristovalensis (Cox, 1870) San Christobal E. scottii (Cox, 1873) Ulawa E. uliginosus (Kobelt, 1891) Maka; Malaita E. unicus (Rensch, 1934) New Georgia E. vicinus (Rensch, 1934) Guadalcanal Genus Euplacostylus Crosse, 1875 (Fiji) E. kantavuensis (Crosse, 1870) Kandavu E. koroensis (Garrett, 1872) Koro E. mbengensis Cooke, 1942 Mbenga E. seemanni (Dohrn, 1861)A Kandavu Genus Leucocharis Pilsbry, in Tryon and Pilsbry, 1900 (New Caledonia) L. loyaltyensis Dautzenberg, 1923 Loyalty L. pancheri (Crosse, 1870)A Grande Terre L. porphyrochila Dautzenberg & Bernier, 1901 Grande Terre Genus Placocharis Pilsbry, 1900 (Solomon Islands) P. acutus Clench, 1941 Guadacanal P. founaki (Rousseau, 1854) Bougainville; Choiseul; Faro; Fulakora; Santa Isabel; Treasury P. guppyi (Smith, 1891) Guadacanal P. kreftii (Cox, 1872) Florida P. macfarlandi (Brazier, 1876) Malaita P. macgillivrayi (Pfeiffer, 1855)A Guadacanal P. malaitensis (Clench, 1941) Malaita P. manni Clapp, 1923 Malaita (Continued)

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Table 1. (Continued) Species

Distribution (islands)

P. ophir (Clench, 1941) P. palmarum (Mousson, 1869) P. paravicinianus (Rensch, 1934) P. strangei (Pfeiffer, 1855) P. stutchburyi (Pfeiffer, 1860) Genus Placostylus Beck, 1837 s. str. (New Caledonia) P. bondeensis (Crosse & Souverbie, 1869) P. caledonicus (Petit, 1845) P. eddystonensis (L. Pfeiffer, 1855) P. fibratus (Martyn, 1784)A P. porphyrostomus (L. Pfeiffer, 1851) P. scarabus (Albers, 1854) Subgenus Basileostylus Haas, 1935 (New Zealand) P. bollonsi Suter, 1908A Subgenus Maoristylus Haas, 1935 (New Zealand; Lord Howe) P. bivaricosus (Gaskoin, 1855) P. hongii (Lesson, 1830)A P. ambagiosus Suter, 1906 Genus Poecilocharis Kobelt, 1891 (Vanuatu) P. bicolor (Hartman, 1889)A P. turneri (Pfeiffer, 1860) Genus Santacharis Iredale, 1927 (Solomon Islands; Vanuatu) S. hullianus Iredale, 1927A S. salomonis (Pfeiffer, 1852) S. fuligineus (Pfeiffer, 1852)

Malaita Florida; Guadacanal; Savo; possibly also San Cristobal Guadacanal Eddystone; Gizo; New Georgia; Rubiana New Georgia; Russell Grande Terre Art Grande Terre Grande Terre; Ame´re´; Ouen; des Pins; Lifou; Mare´; Ouveá; Tiga Grande Terre; Alcme`ne; Balabio; Isie´; Mouac; Ne´ba; Nou; Ouen; des Pins Baaba; Grande Terre; Nenemas; Art; Balabio; Pott; Tanou; Yande´ Great; North East; West Lord Howe; BlackburnB North; Poor Knights; Chicken; Great Barrier; Mokohinau North; Motuopao Espiritu Santo; Aore Erromanga Santa Cruz Erromanga; Aneiteum; Tanna; possibly also Futuna and Espiritu Santo Aneiteum; Erromanga

A

Type species of genus-group taxon. Locally extinct.

B

at least conchologically (i.e. shell morphology). This shell variation has led to the great proliferation of species-group names, many of which are buried in synonymies of currently recognised species. In New Caledonian Placostylus, for example, as many as 141 names at the rank of species, subspecies or variety had been described since the second half of the 19th century, but in a recent revision Neubert et al. (2009) recognised only six valid species. Nonetheless, among these six New Caledonian species Neubert et al. (2009) recognised discrete geographical subspecies based on shell characters: six subspecies in Placostylus fibratus (Martyn, 1784), four in P. porphyrostomus (L. Pfeiffer, 1851), three in P. eddystonensis (L. Pfeiffer, 1851), and two in P. bondeensis (Crosse & Souverbie, 1869). The much more geographically restricted P. scarabus (Albers, 1854) and P. caledonicus (Petit, 1845) were each considered a single entity. That each of these nominal subspecies represents a evolutionarily significant unit (ESU: Waples 1991) has yet to be adequately demonstrated, although Neubert et al. (2009) argued that these geographic subspecies should be afforded recognition in conservation management. The situation in New Caledonia is confounded, especially in the most widely distributed species P. fibratus and P. porphyrostomus, by local population extinctions through loss and fragmentation of habitat, translocation of populations by people (Neubert et al. 2009), and likely interspecific hybridisation (Trewick et al. 2009). Because of high relevance to conservation, there has also been recent reassessments of intraspecific diversity in

endangered New Zealand and Lord Howe Island Placostylus species. All are highly restricted geographically as they occur either on small islands or small areas of the New Zealand mainland. P. bollonsi was originally known from Great Island, North East Island and West Island in the Three Kings Islands group. Powell (1948) subsequently described two subspecies for geographically discrete populations on Great Island but undoubtedly these were relictual following much habitat disturbance by Maori occupation of the island and subsequently by feral goats (Brook and Laurenson 1992, and references therein). Shell morphometric analyses by Brook and Laurenson (1992) and Sherley (1996a) lent some support for the subspecies ordination proposed by Powell (1948) with genetically based variation in shell morphology in P. bollonsi on Great Island. However, their analyses also demonstrated that the shell morphologies of the North East Island and West Island were distinct from all populations on Great Island, despite not being afforded subspecific rank by Powell. Ponder et al. (2003) reported mtDNA analyses indicating that at least the North East Island population may be distinct from populations of P. bollonsi on Great Island. More recent molecular phylogenetic analyses by Buckley et al. (2011) support this conclusion, and indicate a shared mtDNA haplotype in the three nominal subspecies of Great Island, but three distinct haplotypes for the North East Island population. On the basis of their own morphometric analyses, and those of Brook and Laurenson (1992) and Sherley (1996a), coupled with haplotype distribution and low overall genetic diversity, Buckley et al. (2011) found no


support for maintaining the P. bollonsi subspecies of Powell (1948). P. ambagiosus occurs naturally in the northern end of Aupouri Peninsula at the northern extremity of North Island, New Zealand. There it occurs as small remnant populations, from which Powell (1938, 1947, 1948, 1951) recognised 11 subspecies based on differences in shell morphology. Since the work of Powell, 15 additional small populations of P. ambagiosus have been located. Isozyme electrophoresis (Triggs and Sherley 1993) and limited mtDNA analyses (Ponder et al. 2003) indicated some degree of genetic structuring among these populations. The allozyme data exhibited no diagnostic alleles for any of the named subspecies (Buckley et al. 2011). The most recent mtDNA analyses of Buckley et al. (2011) showed considerable haplotype variation within P. ambagiosus that was largely incongruent with taxonomic boundaries. That many P. ambagiosus populations share mtDNA haplotypes is indicative of either ongoing gene flow or very recent divergence, both situations that Buckley et al. (2011) conclude are inconsistent with recognition of subspecies. These authors also found that at least some the variation in shell height and shape can be explained by local environmental factors, as observed earlier by Penniket (1981). Buckley et al. (2011) thus formally synonymised the 11 described subspecies with P. ambagiosus. The third New Zealand Placostylus species, P. hongii, occurs along the east coast of Northland Province, North Island, and on some of the nearby small island groups (Powell 1979; Brook and McArdle 1999; Buckley et al. 2011). Part of this range may be due to translocation by Maori (Buckley et al. 2011, and references therein). As with P. ambagiosus, morphometric analysis of shells showed large amounts of environmental plasticity in P. hongii (Buckley et al. 2011). While variable, subspecific recognition on shell morphology has neither been proposed nor supported by allozyme data of Triggs and Sherley (1993) and the mtDNA data of Buckley et al. (2011). P. bivaricosus of the Lord Howe group has a relict distribution. It is extant in the central and northern parts of Lord Howe Island, albeit as small remnant populations, but the forms of the southern mountains (P. b. etheridgei (Hedley, 1891)) on the island, and that on Blackburn (Rabbit) Island in the lagoon at Lord Howe Island (P. b. cuniculinsulae (Cox, 1872)) are considered extinct (Ponder 1996b). A fourth taxon, P. b. solidus (Brazier, 1889), is known as fossils from Pleistocene calcarenite deposits on Lord Howe Island (NSW National Parks and Wildlife Service 2001). Considerable variation in shell morphology exists within and between some extant populations (Ponder and Chapman 1999; Colgan and Ponder 2001), and a preliminary genetic assessment (Colgan and Ponder 2001) suggested two genetic clades with distinctive shell morphology in the northern and central parts of the Island. Nonetheless, Ponder et al. (2003) found low levels of mtDNA divergence in extant populations and the validity of the subspecies remains to be fully resolved. There has been much less attention paid to infraspecific diversity in Placostylinae from the Solomon Islands, Vanuatu and Fiji. Many species are conchologically variable (Pilsbry 1900; Solem 1959; Delsaerdt 2010) and in part this variation is encapsulated in the synonymies of currently recognised species. Clapp (1923), Clench (1941), Gardner (1994) and Delsaerdt


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(2010) retain subspecies in the taxonomy of Solomon Island Placostylinae, and Cooke (1942) for those of Fiji. For the most part, though, the depth of field surveys and examination of specimens in museum collections has not yet been adequate to delineate infraspecific differentiation in Solomon Island, Vanuatu and Fijian Placostylinae worthy of recognition as ESUs and to support formal description as subspecific taxa. The lack of research focus on infraspecific diversity in Placostylinae in these regions reflects the rudimentary level of understanding of the faunas and the priority on basic inventory work. Furthermore, the absence of assessment of conservation status and identification of species at risk – only now beginning to be addressed (see below) – has precluded a focus on species-level management that demands information of genetically based, infraspecific spatial structure so as to best protect the evolutionary diversity. Detailed systematic revisionary research is urgently needed in the Solomon Islands, Vanuatu and Fiji to document placostyline diversity at all taxonomic levels and provide an evolutionarily coherent framework to guide conservation policy development and prioritise conservation activities. Conservation status A regional overview of the status and conservation effort directed to Placostylinae is summarised in Table 2. Knowledge about the extinction risk within Placostylinae varies enormously across the geographic range of these snails (Table 2). Dearth of knowledge is acute for Vanuatu and the Solomon Islands, where information about taxa is largely limited to rather sparse distribution records and some basic understanding of macroecology (e.g. elevation range, broad vegetation associations, ground-dwelling versus arboreal life strategies). Placostyline species occur throughout Solomon Islands and Vanuatu forests, from near sea level to over 1700 m, and are thus expected to be represented in Key Biodiversity Areas (sensu Langhammer et al. 2007) and CEPF Priority Sites (sensu Aalbersberg et al. 2012) and the few gazetted biodiversity protection areas. However, only weak inferences about the spatial pattern of Placostylinae across the various Solomon and Vanuatu islands can be obtained from the currently available distributional records, and information is entirely lacking as to whether any species is adequately protected in the natural areas networks or, conversely, at risk of extinction due to changes in either habitat extent or habitat quality. There are also no data on population trends. Nonetheless, in both the Solomon Islands and Vanuatu large areas of natural forest below 400 m have been logged in the past few decades or are planned to be logged (Kabutaulaka 2005) and we may infer that lowland populations of Placostylinae are being depleted. Within the Fijian archipelago, Placostylinae are confined to the western high islands of Viti Levu, Vanua Levu, Ovalau, Mbenga, Kadavu, Taveuni, Koro, Gau, and Rambi. IUCN Red List assessments [see IUCN (2012) for description of Red List Categories and Criteria] recently undertaken for these snails (Barker and Brodie 2012; Brodie 2012a, 2012b, 2012c, 2012d, 2012e, 2012f, 2012g, 2012h, 2012i, 2012j; Brodie and Barker 2012a, 2012b, 2012c) indicate that 10 species are threatened (two Vulnerable, six Endangered, two Critically Endangered).

Not assessed.

Variable. Most species single-island endemics, but some widely distributed across several islands. Generally data poor. High. Evidence for range contractions or fragmentation lacking, but little quantitative data. No monitoring.

Red List Assessments

Natural extent of occurrence (EOO)

Population trends

Current Area of Occupancy (AOO): Extent of occurrence (EOO) ratios

4 33 Recent taxonomic revision. Some taxa remain data poor. No phylogenetic data.

Genus richness Species richness Systematic knowledge

Solomon Islands

High. Evidence for range contractions or fragmentation lacking, but little quantitative data. No monitoring.

Variable. Most species single-island endemics, but some widely distributed across several islands. Data poor.

Not assessed.

4 10 Taxonomic revision urgently needed. All taxa remain rather data poor. No phylogenetic data.

Vanuatu

Variable. Most species single-island endemics, but some widely distributed across several islands. Modest levels of data. Medium. Circumstantial evidence for range contractions, but little recent quantitative data. No monitoring. Decline in some lowland populations inferred from surrogate data.

2 14 Taxonomic revision urgently needed. Some taxa remain data poor. Phylogenetic studies have been initiated. IUCN Red List: Barker and Brodie (2012), Brodie (2012a, 2012b, 2012c, 2012d, 2012e, 2012f, 2012g, 2012h, 2012i, 2012j); Brodie and Barker (2012a, 2012b, 2012c).

Fiji

Variable. Most species single-island endemics, but some widely distributed across several islands. Modest levels of data. High to low. Evidence for range contractions and fragmentation in lowland species. Monitoring of some populations indicates decline.

2 9 Recent taxonomic revision. Taxa generally data rich. Recent phylogenetic analyses but confined to two species. IUCN Red List: Mollusc Specialist Group (1996a, 1996b); Bouchet (1996a, 1996b, 1996c); Suggested Red List rankings: Neubert et al. (2009) and Brescia (2011a).

New Caledonia

Table 2. Regional summary of conservation status of Placostylinae

Medium. Evidence for range contraction and fragmentation in the sole species. Monitoring of some populations indicates decline.

IUCN Red List: Sherley (1996a, 1996b, 1996c); New Zealand Threat Classification: Mahlfeld et al. (2012).

IUCN Red List: Ponder (1996a, 1996b); National/ State Red Lists: NSW Scientific Committee (1997), NSW National Parks and Wildlife Service (2001), Australian Threatened Species Scientific Committee (2005). Narrow-range, singleisland endemic. Rather data rich.

Monitoring indicates population stability in one of the three species, and several island populations in a second species. All other populations are declining, except at sites with rodent control.

Low. Evidence for range fragmentation in all three species

Narrow-range endemics. Rather data rich.

1 3 Taxonomic status well established. Recent phylogenetic analyses.

New Zealand

1 1 Taxonomic status well established. Recent phylogenetic analyses.

Lord Howe

F Pacific Conservation Biology G. M. Barker et al.

Active conservation management

Management/recovery Plan

Habitat security

No.

Shifting cultivation; logging; invasive spp. (pigs, rosy wolf snail; Polynesian rat; ship rat; little fire ant); mining. Various invasive ants; Platydemus flatworm. Low representation within protected natural areas network, but growing community interest in conservation. On private land security from logging only by elevation (.400 m) and dissected topography. No.

Current

Emerging

. Shifting cultivation; fuelwood gathering; invasive spp. (pigs).

Threatening processes: Historical

No.

No.

Various invasive ants; Platydemus flatworm. Low levels of legal protection as few gazetted reserves, but growing community interest in conservation. On private land security from logging only by elevation (.400 m) and dissected topography. No.

Shifting cultivation; logging; invasive spp. (pigs, Polynesian rat; ship rats, mongoose).

Shifting cultivation; logging; invasive spp. (pigs, Polynesian rat; ship rats, rosy wolf snail). Various invasive ants; Platydemus flatworm. Low representation within protected natural areas network, but growing community interest in conservation. On private land security from logging only by elevation (.400 m) and dissected topography. No.

Habitat loss; shifting cultivation; fuelwood gathering; invasive spp. (pigs, rats).

Shifting cultivation; fuelwood gathering; invasive spp. (pigs, rats).

Rearing method developed for snail farming and potential translocations; limited active intervention (some predator control but primarily experimental).

Only in respect to limits of harvest for human consumption.

Human harvesting; habitat loss and degradation (mining; fire, grazing); shifting cultivation; fuelwood gathering; invasive spp. (pigs, rats). Human harvesting; shifting cultivation; fire; invasive spp. (pigs, Polynesian rat; ship rats, rusa deer). Various invasive ants; Platydemus flatworm. High levels of legal protection in gazetted reserves, but rather low representation within protected natural areas network. Low security on private land, which predominates.

Yes (maintenance of island biosecurity; predator control, livestock exclusion fences, weed control, and revegetation). All the species considered conservation dependent.

Yes (Parrish et al. 1995; draft replacement plan written but not yet fully implemented).

High levels of legal protection in gazetted reserves, but low security on private land.

High levels of legal protection in reserves and World Heritage site.

Yes (NSW National Parks and Wildlife Service 2001; NSW Department of Environment and Climate Change 2007) Yes (predator control).

Various invasive ants.

Habitat degradation (fire, grazing); invasive spp. (pigs; rats, song thrush)

Localised habitat disturbance by cattle; invasive spp. (song thrush, blackbirds). Various invasive ants.

Habitat loss and degradation (fire, grazing); invasive spp. (pigs, rats, song thrush, goats).

Habitat loss; invasive spp. (pigs, rats, goats).

Diversity and conservation status of Placostylinae Pacific Conservation Biology G

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Extinction risk was considered high, primarily due to limited ‘Extent of occurrence’ (EOO) or ‘Area of occupancy’ (AOO) coupled with decline associated with diminishing extent and/or quality of habitat and, in several cases, the small number of locations under significant threat. Among the remaining species, two are considered of Least Concern, and two as Data Deficient because of taxonomic uncertainties. However, these assessments are recognised as tentative, as there is a pressing need for systematic revision and contemporary distributional surveys. Furthermore, the assessments were heavily reliant on surrogate information such as habitat extent and presence of predatory invasive species. There has been a general absence of population demographic data. Recently initiated and ongoing field surveys by the present authors suggest that at least some placostyline species in Fiji occur in reasonable numbers in the remaining forests of Viti Levu, Ovalau, Kadavu, and Gau. Distributional data for Fijian Placostylinae, collated by Barker and Bouchet (2010), is much more extensive than that available for the Solomon Islands and Vanuatu, in large part due to the shell-collecting interests of European and North American museums and private entrepreneurs during the 19th Century, and the Bernice P. Bishop Museum, Hawaii, in early- to mid20th Century. There have been further distributional surveys of Fijian Islands in the last four decades, but largely confined to Viti Levu and Ovalau and neither have addressed the inadequate survey coverage of large areas within the natural range of Fijian Placostylinae nor provided temporal data on population trends. Placostylinae are currently absent from the dry western side of Viti Levu, but some early occurrence records from forests and cave subfossil deposits from the south-west suggests the former presence of several species in the areas that were once more heavily forested. Dry forests were naturally restricted in extent in Fiji and are now largely confined to northern Vanua Levu, the Yasawa Group, and a few small islands off western and northern Viti Levu, and are thus considered a critically endangered vegetation community type (Keppel 2005; Keppel and Tuiwawa 2007). That these dry forests have not been surveyed for Placostyline snails is a serious omission given the significant presence of Placostylinae in tropical dry forests of New Caledonia (see below). All other occurrence records for Fiji are from rainforests, at elevations from near sea level to over 1000 m, and data suggest that Placostylinae are likely present in all recognised conservation areas and priority sites as defined by Conservation International (2007), Kretzschmar (2000), Government of Fiji (2001), Masibalavu and Dutson (2006), and Olson et al. (2010). As with the Solomon Islands and Vanuatu, information is generally lacking as to whether any species is adequately protected in the natural areas network. Further, despite the greater availability of distributional records, the current level of biological knowledge of Fiji species is poor. The present authors have initiated studies to address this gap with quantitative surveys along forest line transects to estimate abundance and vegetation associations in several species and several locations. Traditional practices of subsistence gardening and agriculture probably had minimal impact on Placostylinae in Fiji as we have observed species prevalent in both primary and secondary forest in the vicinity of villages. However, it is unknown to what degree these and other pressures have led over time to a shift

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in the composition of land snail communities, inclusive of Placostylinae. We consider forest degradation and loss through agricultural clearance, plantation establishment and logging in remaining tropical rainforests of Fiji, primarily because of the scale of disturbance, to have far greater adverse effect on Placostylinae than traditional practices of subsistence gardening. The invasive species impacting on Placostylinae in the Solomon Islands, Vanuatu and Fiji forests have not been studied, but can be inferred from experiences elsewhere to include feral pigs (Sus scrofa Linnaeus, 1758), ship (black) rats (Rattus rattus (Linnaeus, 1758)), Pacific rat (Rattus exulans (Peale, 1848)) and, in some areas of Fiji, mongooses (Herpestes auropunctatus (Hodgson, 1836) and H. fuscus Waterhouse, 1838). Placostyline shells with evidence of pig and rodent damage have been observed, but presently there is no information as to the significance of this source of mortality. In relation to the lowland rainforest of the Solomon Islands, Peake (1968: 327) observed that ‘the practice of keeping large herds of pigs has possibly had a more disastrous effect [than forest clearing around villages] on the flora and fauna over large areas. The pigs must kill or eat many animals and young plants; while the continual rooting disturbs the litter and soil, permitting rapid desiccation and the creation of an unfavourable environment’. The impacts of ship rat and mongoose may be most intense around the margins of forests as these predators are thought to be edge specialists (Olson et al. 2006). The New Caledonian taxa Placostylus fibratus, P. eddystonensis and P. porphyrostomus were assessed as Vulnerable using the IUCN Red List criteria in 1996 (Bouchet 1996a, 1996b, 1996c) but these assessments have been recognised as being in need of updating, given the ongoing changes in habitat extent and quality wrought by human land-use and impacts from invasive species. Brescia et al. (2008: 120) argued ‘Taking into account the small geographic range of these species (less than 100 km2, in some cases restricted to a single locality), the population declines evident due to loss of native forests (99% for dry forest and more than 70% for humid forest), and the severe fragmentation of many of these populations, P. caledonicus, P. bondeensis, P. scarabus and P. eddystonensis should be revised to Critically Endangered. The status of P. fibratus should also be changed to Endangered, given the estimated population decline due to the habitat degradation and the levels of exploitation and other factors implicated in the population decline’. As part of a taxonomic revision of New Caledonian Placostylus, Neubert et al. (2009) proposed Red List rankings for subspecies of P. fibratus, P. porphyrostomus and P. eddystonensis but failed to assess these taxa at the species level. While it is clear from Neubert et al. (2009) that at least some subspecies are at high risk of extinction (see Table 2), the fact that the 1996 and 2009 assessments were undertaken using different taxonomic ranks, and with emphasis on different Red List criteria (population size reduction, and geographic range, respectively) limits our ability to gauge temporal changes in level of extinction risk. It is also unclear as to what degree species concepts varied between the 1996 and 2009 assessments. Neubert et al. (2009) also proposed Red List rankings for the species P. scarabus and P. caledonicus and subspecies of P. bondeensis,


all of which had not previously been assessed. The assigned ranking of Vulnerable (B2a, b) reflects the fragmented nature of the populations and continuing decline in AOO of P. scarabus and P. caledonicus. Both subspecies of P. bondeensis were assessed as Endangered (B2a, b), distinguishing this species from P. scarabus and P. caledonicus by its much smaller AOO. There is urgent need to formalise the Red List rankings proposed by Neubert et al. (2009) and develop and implement species recovery plans for New Caledonian Placostylus species. A principal driver of extinction risk in New Caledonian litterdwelling Placostylus has been loss and fragmentation of forest habitat (Neubert et al. 2009). This has been particularly acute for the dry sclerophyll forests, now reduced to small patches scattered across much of the west coast of New Caledonia and amounting to less than 1% of its original extent (Bouchet et al. 1995; Gillespie and Jaffre´ 2003). In the last two decades, a conservation program for the dry forest (Programme Foreˆt Se`che) has been established between provincial administrations, research organisations and conservation NGOs. Within that program, population levels and recruitment of Placostylus have been evaluated at a few sites where P. porphyrostomus mariei (Crosse & Fischer in Crosse, 1867) persist (Brescia and Po¨llabauer 2004, 2005; Brescia et al. 2008). However, the extent of fragmentation and loss of dry forest habitat has led, even in recent decades, to extinction of many Placostylus populations, while others are extant but very small and highly isolated (Neubert et al. 2009). Rainforests naturally occupied ,70% of the New Caledonian land area, but now occupy ,20% (Mittermeier et al. 1999; Sloan et al. 2014). Large blocks of rainforests persist only in upland areas of complex topography. At lower elevations rainforests have been cleared for agriculture, or severely fragmented and degraded by logging, mining and fires, giving rise to Melaleuca savanna, or secondary maquis on ultrabasic rocks. Logging, mining and fires continue to degrade the landscape. Placostylus naturally occurred throughout the rainforests, over an elevational range from near sea level to over 1000 m. There is some evidence that range contractions have occurred in several Placostylus species despite the retention of rainforest habitat. For example, Neubert et al. (2009) documented the extinction since the late 19th century of Placostylus eddystonensis bavayi (Crosse & Marie in Crosse, 1868), endemic to the Mount Mou area north-west of Noumeá, despite seemingly intact forests remaining from 300–400 m to the summit. The arboreal Leucocharis were evidently once widespread in New Caledonia, but extant populations are now represented only by L. pancheri (Crosse, 1870) in the vicinity of Boulari in Province Sud. This taxon is very poorly known. IUCN Red List assessments by Mollusc Specialist Group (1996a, 1996b) considered Leucocharis loyaltiensis Dautzenberg, 1923 and L. porphyrocheila Dautzenberg & Bernier, 1901 to be extinct. The protected area network of New Caledonia is diminutive, covering just 2.8% of the land area, but is increasingly augmented by areas managed jointly by local communities, New Caledonian government authorities and international NGOs. There have been no critical analyses of recent distributional records of Placostylus and Leucocharis to determine the level of representation afforded to Placostylinae by this network of conservation areas. However, placostyline species have been


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triggers in designation of Key Biodiversity Areas (Conservation International 2011). Placostylus are protected under legislation in Province Nord and Province Sud. The invasive species most adversely affecting Placostylus in New Caledonia are ship rats, Pacific rats, mice (Mus musculus (Linnaeus, 1758)) and pigs (Po¨llabauer 1995; Brescia 2004, 2005, 2011a, 2011b; Brescia and Po¨llabauer 2005). The rosy wolf snail (Euglandina rosea (Ferussac, 1818)) introduced in 1977 and 1980 as a control agent for the giant African snail (Achatina (Lissachatina) fulica Bowdich, 1822), has not widely established and has not impacted placostyline populations (Neubert et al. 2009). In contrast, predation by rodents and pigs limit recruitment in Placostylus populations, with greatest impact on relictual populations in fragments of both dry forest and rainforest. A recent survey of such populations in Province Nord, for example, showed that the adult snails predominate and that future persistence of these Placostylus populations may be compromised by both heavy rodent predation on juveniles and habitat modifications by feral ungulates, especially Rusa deer (Cervus russa timorensis (de Blainville, 1822)) (F. M. Brescia, pers. comm.). Experimentally, it has been demonstrated that recruitment of juvenile snails can be enhanced by rodent control (Brescia 2011a) and an experiment to restore a Placostylus population by long-term rodent poisoning in a patch of dry forest on Grand Terre is in progress (F. M. Brescia, pers. comm.). Despite the recognition of Placostylinae as highly endangered, with causative agents of decline having been identified, recovery plans have yet to be developed and implemented by the New Caledonian government. To address this gap, Brescia (2011a) formulated recovery plans for each Placostylus species as part of a Ph.D. project. A. fulica has invaded Placostylus habitat in many areas but its impact on the native snails through competition for space and food remain unclear. As summarised by Brescia et al. (2008) and Neubert et al. (2009), all the forms of New Caledonian Placostylus are considered edible and utilised by both the Melanesian Kanak peoples and Europeans alike. In particular, the ‘escargots de l’Ile des Pins’ (Placostylus fibratus fibratus and P. f. guestieri (Gassies, 1869)) has become the favourite with the Noumea restaurant industry and is harvested from the field in considerable numbers. To prevent over-harvesting, regulation was passed by the New Caledonian Government (De´libe´ration, Assembleé de la Province Sud, 20 December 1994) prohibiting both the collection of live Placostylus on l’Ile des Pins between 1 May and 30 September, and the export of live (unprocessed) snails outside the island. An amendment in 2000 (De´libe´ration 26-2000/APS) allows collection and consumption of Placostylus throughout the year on l’Ile des Pins but prohibits export to the mainland of both live and cooked snails. As noted by Brescia et al. (2008), this law has reduced the number of adult Placostylus collected on the island two-fold (to ,100 000 snails per year). As a biological entity, P. f. guestieri is not considered threatened with extinction, but there is concern for its future as a sustainable economic resource (Neubert et al. 2009). The Lord Howe P. bivaricosus was assessed using IUCN Red List criteria as Critically Endangered (B1þ2abcde) by Ponder (1996a), and its subspecies P. b. cuniculinsulae (Cox, 1872) as Extinct by Ponder (1996b). The other subspecies P. b. etheridgei has been considered likely extinct (NSW Scientific Committee

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1997), but in fact may survive as several small, isolated populations, based on the identification of hatchling snails from leaf litter collected from the southern mountains in the 1970s (Ponder and Chapman 1999). More recently, NSW National Parks and Wildlife Service (2001) and the Threatened Species Scientific Committee (2005) of the Australian Commonwealth listed the species as Endangered (Table 2). A recovery plan was published in 2001 and the species accordingly managed by the Lord Howe Island Board (NSW Department of Environment and Climate Change 2007). Specific objectives of the Plan include: identify habitat and populations; identify and mitigation of current threats; support and coordinate research relevant to the species’ recovery; encourage community awareness of the status of the species and threats to its survival; and support community involvement in its recovery. Captive breeding methods have been investigated (e.g. Hutton 2010) but as yet not employed to aid the species’ recovery. In recent years the Board’s focus in respect to P. bivaricosus has been with reducing predation by ship rats, which has been identified as the primary threatening process (NSW Scientific Committee 2000). To this end the Board currently maintains ,1000 rat bait stations in designated baiting areas across the island. While the Board undertakes monitoring of P. bivaricosus, to our knowledge the results have not been published. The Board has also determined the feasibility of eradicating rats from Lord Howe and in July 2012 the New South Wales and Australian Governments announced a joint funding arrangement for the Lord Howe Island Rodent Eradication Program, through the New South Wales Environmental Trust and the Australian Government’s ‘Caring for Our Country’ program. The three New Zealand Placostylus species are naturally very restricted geographically, and each has been severely affected by human land-use and invasive species over the past few centuries. They are protected under the Wildlife Act 1953, have been under active management since the early 1980s, and are currently managed within the context of a Recovery Plan (Parrish et al. 1995). The Three Kings Islands habitat of P. bollonsi was strongly modified on Great Island by Maori occupation and subsequently by feral goats. The departure of Maori and removal of goats from Great Island, and the subsequent regeneration of broadleaf trees, has led to a substantial increase in the number of P. bollonsi (Brook and Laurenson 1992; Brook 2003). The species was ranked as Vulnerable (D2) in the IUCN Red List (Sherley 1996b) and Nationally Endangered (B2/1) in the most recent iteration of the New Zealand Threat Classification (NZTC) (Mahlfeld et al. 2012). Despite the ongoing recovery, the species is regarded as conservation dependent in that maintenance of island biosecurity, as prescribed in the Recovery Plan, is vital to preventing establishment of rodents and reducing the risk of wildfires. Purchased by the New Zealand Government from Maori landowners in 1908, the Three Kings Island Group is now a Nature Reserve for the preservation of flora and fauna, and managed by the Department of Conservation. The original forest habitat of P. ambagiosus on northern Aupouri Peninsula has been severely depleted and fragmented by Maori and European occupation, such that native coastal forest now covers only ,3% of the area and is largely replaced by native shrublands or exotic grasslands (Lux et al. 2009).

G. M. Barker et al.

Despite legal protection in various classes of reserve, the remaining forests and shrublands continue to be degraded by domestic or feral browsers and grazers (cattle (Bos taurus Linnaeus, 1758), horses (Equus caballus Linnaeus, 1758), Australian brushtail possums (Trichosurus vulpecula (Kerr, 1792)) and pigs) (Parrish et al. 1995) and by fire. P. ambagiosus persists only as small remnant populations, both in the primary shrublands and forest and in the induced shrublands. The species was ranked as Vulnerable (B1þ2abcde) according to IUCN Red List criteria by Sherley (1996c) and Nationally Vulnerable (C3/ 1) according to the NZTC by Mahlfeld et al. (2012). In the case of P. hongii, the coastal forest habitat in eastern Northland and adjacent islands have been subject to forest clearance and fragmentation for Maori and European settlement and agriculture. Much of the remaining native coastal forests and shrublands are legally protected as conservation reserves, and while some P. hongii populations are evidently more-or-less stable on the mainland and islands alike, some mainland populations in intact forest have gone extinct and others are verging on extinction because of high levels of rodent predation (see Brook and McArdle 1999). Their medium- to long-term persistence is doubtful without predator control. The species was ranked as Vulnerable (C1þ2a, D2) according to IUCN Red List criteria (Sherley 1996d) and more recently Naturally Uncommon according to NZTC criteria (Mahlfeld et al. 2012). The largest known population of P. hongii occurs on The Poor Knights Islands, and the Recovery Plan places high emphasis on maintenance of island security analogous to the situation in the Three Kings Islands. Both P. ambagiosus and P. hongii are subject to significant predation by various introduced vertebrate species, not least rodents. Studies since the 1980s have both demonstrated that rodents impose significant constraints on juvenile recruitment in Placostylus populations, and demonstrated that long-term pulse poisoning of rodents in remnant ‘islands’ of native habitat on the New Zealand mainland can be beneficial to the recovery of snail populations (Sherley and Parrish 1989; Parrish et al. 1995; Sherley et al. 1998). Management of rodent populations is a central theme in current recovery work directed at P. hongii and, in particular, P. ambagiosus. Conservation imperatives There are several reasons why Placostylinae demand conservation action: Extinction threat The most compelling imperative for action is the identification, either via the IUCN Red List assessment process or through national alternative threat classification schemes, of species at high risk of extinction. The statuses of placostyline species have already been assessed in New Zealand, Lord Howe Island, New Caledonia and Fiji (Table 2). In the case of New Zealand and Lord Howe Island, the species identified at risk are naturally very narrowly distributed and impacted by anthropogenic disturbances over several centuries. Their identification as being at risk has directly led to formulation of recovery plans and active conservation management by the respective government authorities (Table 2). In the case of New Caledonia and Fiji, the


species of Placostylinae are generally not so geographically restricted, but ongoing anthropogenic disturbances are reducing and fragmenting their AOO, and reducing local densities, thus bringing populations in some species rapidly to a point analogous to that in New Zealand and Lord Howe Island. In both New Caledonia and Fiji there are local initiatives to address threatening processes, but as yet no formal implementation of recovery plans by government authorities. Only 31% of the Melanesian–New Zealand species have received assessment for the IUCN Red List. Of countries where Placostylinae occur, only the Solomon Islands and Vanuatu have yet to assess the status of species (Table 2). The very limited information presently available for the Solomon Islands and Vanuatu suggests that the placostyline species there are not in immediate peril but the scale of anthropogenic environmental change wrought by ongoing logging of forest habitat, and the emergence of invasive species as new threats, suggests that the situation is highly dynamic and should be carefully monitored. The immediate assessment of several narrow-range lowland species is warranted. The Solomon Islands and Vanuatu have emerging science and conservation capabilities, and timely input by external expertise in land snail systematics and ecology is needed to assist with Red List assessments and build local capability and capacity. Cultural significance Through their close association with the land and forests, the indigenous peoples of Melanesia and New Zealand were well acquainted with, and in some cases treasured, placostyline land snails. Unfortunately, many aspects of this cultural link have not been well documented, and accordingly deserve much more study. Placostylinae are among the world’s largest pulmonate snails and certainly amongst the largest snails native to the Melanesia–New Zealand region, and are conspicuous by their naturally high densities and often arboreal habit. Typically, placostyline species, subspecies, or distinctive conchological forms are restricted geographically, and thus contribute to a sense of place. The familiarity is acknowledged with naming of these snails in the local languages, including, for example, ‘Pupuharakeke’ in Maori, ‘Sici ni vanua’ in Fijian, ‘Ngho’ and ‘Hibu’ in Kwenii (Ile des Pins). Placostylinae feature in Maori legend (e.g. Wilkinson 2012), are utilised widely for decoration and jewellery (Brenchley 1873; Brescia 2011a), are fashioned into fishhooks (Reinman 1967), and are utilised as both traditional food and medicine by the Kanak peoples of New Caledonia (Po¨llabauer 1995; Brescia et al. 2008; Brescia 2011a). In New Caledonia today, P. f. guestieri is priced for the Ile des Pins restaurant industry. Old pressures and new As briefly reviewed above, Placostylinae throughout their range have been subject to considerable pressures from anthropogenic activities over the past few centuries. It is clear from experiences in New Zealand, Lord Howe Island and New Caledonia that these pressures can drive placostyline populations towards extinction and threaten the survival of species. Only in the case of P. bollonsi in the Three Kings Islands has local anthropogenic influence ceased (but is subject to maintenance of island


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biosecurity) and the snail populations recovering in association with ecosystem recovery. Similar recovery of P. ambagiosus has occurred on Motuopao Island following rodent eradication, although there are still issues with ongoing habitat degradation through adventive weeds and helicid snails on that island. With the exception of P. bollonsi in the Three Kings Islands, the other New Zealand Placostylinae continue to be exposed to anthropogenic perturbations over all or part of their range, and are likely in decline. There are programs in New Zealand, Lord Howe Island and New Caledonia to mitigate some threatening processes at some places. There is an urgent need to properly evaluate which placostyline species are most at risk of extinction, prioritise these for conservation management, and implement recovery programs. Even in New Zealand and Lord Howe Island, where recovery plans are in place and acted upon, the current intensity and spatial extent of conservation management activities is probably not sufficient to arrest decline in P. ambagiosus, P. hongii and P. bivaricosus. Assessment of extinction risk, either via the IUCN Red List assessment process or through national alternative threat classification schemes, should be seen as only the first step. Proper understanding of the threatening process is critical if mitigation measures are to be effective. Often there are complex interactive effects of habitat modification and species invasion on native species decline (Didham et al. 2005, 2007; Norbury et al. 2013). Habitat loss is clearly a primary driver of native species decline. However, habitat modification may also reduce native species abundance. Industrial logging causes moderate to heavy forest disturbance (depending on logging intensity), and while many native species can persist in logged forests (albeit at reduced densities), many perish. Of equal importance is that, by creating networks of forest roads and broken canopies, logging can facilitate other forms of human exploitation of forests by hunters, miners, ranchers, and slash-and-burn farmers, which can further severely degrade or destroy forests (Laurance 2004). Invasive species may also take advantage of the new environment, which in turn can alter disturbance regimes. Invasive species can, for example, significantly alter habitat structure, resource availability, and dynamics of parasitism and disease, leading to suppression or enhancement of the relative abundance of native species without necessarily being the primary driving force behind community change (Didham et al. 2005, 2007; Smith and Banks 2014). Edge-affected habitats exhibit intensified species interactions relative to interior habitats, resulting in shifts in community composition that can extend considerable distances into seemly undisturbed forest (Ewers and Didham 2008; Berge`s et al. 2013). The burgeoning human populations of Melanesia, especially of the Solomon Islands and Vanuatu (Kingsford et al. 2009), will bring increased pressures on biodiversity with changes in landuse, extractive harvest and establishment of invasive species. The emergence of new threats from invasive species in Melanesia suggests a need for both ongoing biosecurity vigilance and monitoring of the status of placostyline species. Examples of recent invaders that have the potential to impact on Placostylinae either directly through predation or competition, or indirectly through ecosystem cascades, include the predatory flatworm Platydemus manokwari de Beauchamp, 1962; various ants, among which are the little fire ant

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(Wasmania auropunctata (Roger, 1863)), yellow crazy ants (Anoplolepis gracilipes F. Smith, 1857) and the African bigheaded ant (Pheidole megacephala (Fabricius, 1793)); and the semislug Parmarion martensi Simroth, 1893. The giant African snail, long established in the Solomon Islands, Vanuatu and New Caledonia, has the potential to compete directly with Placostylinae but, for the most part, ‘occupies gardens, fallows and degraded and secondary forest, which are all habitats unsuitable for Placostylus, so in essence the native and the introduced giant snails are not directly competing, except in small patches of degraded dry forest on the west coast (Brescia and Po¨llabauer 2004)’ (Neubert et al. 2009: 121–122). Nonetheless, in recent years A. fulica has become much more pervasive in New Caledonia and is now the most dominant snail in many distributed and primary forest sites alike (Brescia 2011a). In these situations direct competition with native snails is indicated by changes in population structure of Placostylus (Brescia 2011a). Several predatory land snails, including the rosy wolf snail, have been introduced extensively in Melanesia as putative biological control agents of the giant African snail. They have not had the devastating effects on native land snails reported for other regions of the Pacific, in large part due to as yet limited distribution within the Melanesian islands. The giant African snail and the rosy wolf snail are currently absent from Fiji. Placostylinae can achieve very high local biomass on account of both large body size and high densities per unit area (Choat and Schiel 1980; Penniket 1981; Brook and Laurenson 1992; Stringer et al. 2004; Murphy and Nally 2004; Brescia et al. 2008; Brescia 2011a). As such, they can dominate the grounddwelling detritivorous [detritus-feeding] and arboreal phylloplane-grazer [grazing microbial biofilms of leaves and trunks] invertebrate guilds of the forests and shrublands of the Melanesian–New Zealand region. By virtue of a dispersed food supply and their large biomass, these are animals that require large amounts of living space, and are the guild members likely most-sensitive to changes in the biotic and abiotic environment. Ease of sampling and monitoring Large-bodied Placostylinae (as with Camaenidae and Trochomorphidae in Melanesia; Rhytididae in New Zealand) offer much as potential foci of rapid assessment and monitoring in local conservation, biodiversity management, and forest stewardship programs. The large size offers considerable advantages relative to many other members of the sympatric land snail communities, which are small to minute, in that Placostylinae are easily observed in situ and thus data are easily gathered without undue habitat disturbance. In particular, Placostylinae are amenable to mark–recapture studies as the shells of live animals can be marked (or otherwise identified) and detected later by recapture or resighting. In addition to estimating population size and survival rates, mark–recapture methods can be used to evaluate impacts of threats on survival, record population trends, collect information for population viability analyses, and set performance targets against which responses to management can be measured (Sutherland 1996; Lettink and Armstrong 2003; Janks and Barker 2013). The mark–recapture method is most useful when it is not possible or practical to count all the individuals in the population, provided two or more visits to the site are possible.

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The great utility of the mark–recapture method for study of Placostylinae has been amply demonstrated by Po¨llabauer (1995), Brescia (2007, 2011a) and Brescia et al. (2008) working on Placostylus in New Caledonia, and by Choat and Schiel (1980), Sherley and Parrish (1989), Parrish et al. (1995, 2014), Sherley et al. (1998), Stringer et al. (2004, 2014), and Stringer and Parrish (2008) on Placostylus in New Zealand. Role as conservation flagships Noted conservationist Aldo Leopold heralded the importance of landowner stewardship in conservation of biodiversity (Leopold 1949). He applauded wildlife sanctuaries, reserves, and parks but perceived that nature needed nurturing in backyards, communities, and on working landscapes. Clan ownership and stewardship of Melanesian and northern New Zealand forests offers great opportunity for such nurturing and for use of Placostylinae as flagships. Engagement of local communities in conservation is critical to achieving outcomes for these snails. As discussed above, these large, often conspicuously beautiful shelled elements of the forest faunas are familiar to, and often valued by, indigenous peoples throughout the region. They are highly vulnerable to forest degradation and thus sensitive indicators of habitat condition, yet highly amenable to study and monitoring with the most basic training and equipment. Data on placostyline land snails will broaden the taxonomic scope of current conservation awareness, policy and management efforts at both local and government levels. Priorities and methodological issues in addressing placostyline conservation Aspects of biology relevant to conservation have been extensively studied in New Zealand, Lord Howe Island and New Caledonian Placostylinae of the genus Placostylus. This body of work has been reviewed by Brescia et al. (2008), Brescia (2011a), Buckley et al. (2011) and others, and will not be repeated here. Rather, we highlight four priority areas for advancing the conservation of Placostylinae, especially in Melanesia, and discuss the most pressing methodological issues. Assessment of extinction risk The IUCN Red List criteria are a useful starting point when considering what data would be useful in assessing the conservation status of species, and how best to collect such data. We suggest that Criteria A and B are most relevant to Placostylinae that have not yet been assessed, specifically those of the Solomon Islands and Vanuatu. Criterion A: Population reduction (over 10 years or three generations) This criterion is based on the reduction of the number of mature individuals of a given species. Monitoring population changes requires a sampling program replicated at least twice (current population size compared with an estimate from the past or a projection for the future), 10 years apart to meet the IUCN criteria, and further sampling efforts would be required to distinguish between natural fluctuations and a real change. The situation is tractable for Placostylinae, as their large body size,


ease of detection, sedentary lifestyle and low dispersal capabilities, allow abundance data (density per unit area or numbers found per unit sampling effort) to be readily obtained from either simple counts of individuals in area-defined plots or using mark–recapture methods. The main limitations to utilising Criterion A are 2-fold: (1) The number of sites that need to be sampled to obtain a reliable estimate of abundance for a species may be beyond the available resources, especially in heterogeneous landscapes where abundance might greatly vary spatially. This limitation is particularly acute where there are many species to be assessed, and where access to sites is difficult, as for example, in the case of Placostylinae of the Solomon Islands and Vanuatu. The solution is probably best achieved by adopting a predictive framework that combines stratified sampling of both species and environment and subsequent spatial modelling. (2) The 10-year interval is generally longer than political tenure cycles and project funding cycles, with contingent likelihood of failure to achieve the decadal repeat measure. Nonetheless, the great utility of time series estimates of abundance in many aspects of conservation management should encourage the establishment of permanent plots at which placostyline census data could be periodically obtained. Cardoso et al. (2011) suggest that to improve the applicability of the IUCN Red List to invertebrates, Criterion A could be modified by using decline in AOO as an alternative to abundance, but based on the same percentage thresholds as population reduction. They suggest that AOO can be estimated by combining spatial data on extent of habitat and records of habitat patch occupancy, or predictive modelling of extent of occupied habitat. But see comments below under Criterion B. Criterion B: Geographic range This criterion is based on the range size of a species, either as EOO or AOO, coupled with at least two of three other symptoms of risk related to abundance or range: severe fragmentation or limited to a few locations; actual or projected continuing decline; extreme fluctuations. Lewis and Senior (2011) considered AOO to be the only existing criterion that can be properly applied to most species. We note, however, that both AOO and EOO are extremely challenging in taxa and regions where biodiversity inventory and population ecology are in their infancy, such as is the case with Placostylinae in the Solomon Islands, Vanuatu and, to a lesser degree, Fiji, because: (1) the distributions of many species are incompletely known, and much distributional data are historical such that the habitat conditions under which early records were collected (e.g. 19th Century) may no longer apply; (2) spatial modelling as estimators of AOO and EOO, as suggested by Cardoso et al. (2011), is constrained by scarcity of occurrence records for naturally or anthropogenically impacted rare species (often ,10 records per species), and (3) the magnitude of the task is huge given that numerous species occur across extensive island archipelagos with often limited access.


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It is clearly important to build on existing data, so attempts to estimate EOO and AOO should start with collation of distributional data encapsulated in taxonomic literature and museum specimen collections relevant to Placostylinae in the region. With these data at hand, new stratified sampling programs can be developed to strategically fill gaps and reduce the influence of spatial biases. In the absence of further sampling, all species of Placostylinae of the Solomon Islands and Vanuatu would have to be classified as Data Deficient, an unsatisfactory situation in light of the extent of habitat changes occurring in the region. Criterion C: Small population size and decline This criterion is based on the total number of individuals in a species and the possibility of this number declining, or fluctuating greatly. Rarely is it possible to estimate the total number of individuals in an invertebrate population, although such estimates might be obtained for placostyline species by modelling mark–recapture data from sampling a population confined to a habitat patch (e.g. forest remnant, small island). That populations are in decline, or fluctuating, may be determined by periodically repeating the sampling (at 10-year intervals to meet the IUCN criteria). We consider this criterion as being of interest only after estimates under Criteria A and B have established that the species is both very narrowly distributed and in decline. Identification of threatening processes and appropriate mitigation strategies When considering the recovery of threatened species, the first task is to identify the cause of decline. This is often reduced to the task of identifying the threatening processes, yet may often be too simplistic when multiple predisposing factors are operating in the population. As Didham et al. (2007: 472) point out, ‘y drawing a distinction between the proximate versus ultimate causes of population decline, and between the factors that directly or indirectly limit population recovery will greatly increase our ability to manage threatened species more effectively. y Pragmatically, these issues matter for conservation managers because focusing attention on the direct, proximate agent perceived to be limiting population recovery might not necessarily result in long-term success’. Because of potential interactions between habitat loss and modification with invasive species (e.g. Norbury et al. 2013), the identification of threatening processes may be best achieved through ecosystem-level manipulation experiments where, for example, specific invasive species are controlled at sites along gradients of landscape modification. In developing and applying mitigation strategies a major challenge is the proper interpretation of changes in abundance of native species that might occur in the short term following ecosystem perturbation (such as the establishment of an invasive species) or following experimental ecosystem manipulation (such as control of a predatory invasive species). Changes in the abundance in one or more life stages in the native species, relative to reference sites is commonly interpreted and extrapolated to suggest that the perturbing or manipulated factor is adverse to the native species in question. In most cases, those are

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the best data available. However, it should be noted that marked changes in mortality in a particular part of the life cycle may have no real impact on the population trend of the native species if variation in that stage is not critical to population regulation (i.e. an upper limit imposed on their growth via densitydependent feedback). When assessing effects of disturbance or, conversely, ecological release when that disturbance is removed, there is often little consideration given to dependency of population dynamics and thus intergenerational trends in abundance on the level of irreplaceable mortality (Thompson 1955; Morris 1965) operating in the population. It has yet to be tested, for example, if the high mortality observed in juvenile Placostylus caused by invasive rodents (e.g. Sherley and Parrish 1989; Parrish et al. 1995; Sherley et al. 1998; Brescia et al. 2008; Brescia 2011a) is limiting to populations in which the adults are long-lived, have a long reproductive life and are highly fecund. It is possible that juvenile mortality in Placostylus is naturally high in undisturbed forests and mortalities imposed by rodents simply substitute for mortality imposed by natural processes. There is emerging evidence that such rodent impacts on population dynamics in Placostylus are conditional on other aspects of ecosystem integrity, such as prior fragmentation of habitat, and presence of other invasive species (e.g. Brescia et al. 2008; Brescia 2011a). At the ecosystem level, a perturbation that alters the abundance and quality of forest floor leaf litter may have profound effects on the temporal stability of abundance in a native placostyline if its populations are naturally primarily regulated by bottom-up processes. Conversely, such changes in resource due to ecosystem perturbations will have little impact for a placostyline species whose populations are primarily regulated by top-down trophic interactions. Current knowledge of placostyline biology would indicate that populations are naturally regulated by bottom-up processes, but it is possible that invasive species such as rodents, pigs, and potentially Platydemus flatworms may cause a switch to top-down regulation. Proper elucidation of ecosystem perturbation effects on placostyline species can only be achieved by appropriate comparative or manipulative experiments coupled with both monitoring that spans several generations and analyses of key factors in population regulation and their density dependence. An often overlooked difficulty in impact assessment is that invasive species incursions into an area are generally not random in respect to environment. Thus invaded sites and available invader-free control sites may be inherently different in respect to environmental character, albeit often subtle, and thus likely to vary in biodiversity and ecosystem processes. Critical to robust interpretation of results is the proper environmental characterisation of invaded sites and candidate noninvaded control sites, so as to select control sites that match the invaded sites as much as practicable. Several aspects of the environment may be characterised readily from available highresolution spatial databases, including remote-sensed spectral signals and topography, but data gathered ‘on the ground’ for soil physics and chemistry, vegetation composition, and indicators of any prior anthropogenic disturbances will also be helpful. Armed with this environmental information, it is then possible to adopt appropriate statistically robust experimental designs such as (1) replicated pairs of invaded and non-invaded

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sites that can be analysed in paired groups’ t-test, Wilcoxon-test or McNemar’s-test; (2) stratified-random allocation of invaded and non-invaded sites to replicates for analysis of variance; or (3) stratified-random allocation of invaded and non-invaded sites along one or more environmental gradients that can be modelled in regression or Bayesian approaches to gradient analysis. An alternative approach in ecosystem manipulation studies is the before–after–control–impact (BACI) experimental design. Of course, options available will depend on the dispersion of the threatened native species – whether it occurs at a single site or multiple sites. Irrespective of the experimental approach, there should be flexibility to include additional measures of ecosystem impacts, as invasive species establishment often leads to novel ecologies, which generally are difficult to predict a priori but are important to document if both understanding of invasion processes and mitigation of impacts are to advance. There is also a critical need to collect data on densities of the invasive species in order to develop an understanding of the relationship between invader density and levels of impact on Placostylinae. Monitoring outcomes It is critical to monitor the outcome(s) of threat mitigation actions to ensure that species recovery occurs, to confirm the cause-and-effect hypothesis(es) that was foundational to initiating those actions, and to establish the level of return on conservation investment. A trade-off exists between the funding allocated to undertaking conservation action, and to monitoring and evaluating conservation outcomes. Therefore, it is important that appropriate indicators are chosen for measuring and monitoring outcomes of management actions. From a species conservation perspective, the ultimate outcome measure is the change in the status of the species under management, such as listed in IUCN or national Red Lists. A major challenge is to develop management options that are self-sustaining, so monitoring should include indicators of conservation dependence on ongoing investment of resources. At a higher level, monitoring and evaluation are crucial components of an effective conservation management program, as the information gained can establish the degree of success of management and consequently influence policy and future investment into conservation actions. A key challenge is maintaining input into ecosystem manipulation programs, including conservation management operations, for sufficient length of time to fully gauge the potential gains for the native species. Short-term changes in abundance of the threatened species do not necessarily translate to improved species security due to population processes acting out over several generations (see earlier discussion under identification of threatening processes). Such processes can include re-establishment of a reproductively functional cohort; build up in densities towards local carrying capacity; delayed density dependency in mortality; and emergence of novel ecologies in both the native species under management and various invasive species resident within the ecosystem. IUCN defines generation length as the average age of parents of the current cohort, and therefore reflects the turnover rate of breeding individuals in a population. To adequately assess potential outcomes of ecosystem manipulations, monitoring


assessment should occur for at least five generations, which for at least some Placostylinae that are reproductively adult for 5–30 years (Brescia et al. 2008, and references therein), means definitive statements about outcomes may not be possible for a quarter of a century or more. Advancing understanding of evolutionary relationships Molecular phylogenetic analyses are urgently needed to provide an evolutionary framework for taxonomic revision and to underpin development of both conservation policy and species recovery plans. The evolutionary history of lineages is increasingly being used to establish conservation priorities, to complement other approaches such as IUCN Red List assessments that establish the imperilment of species based on criteria that include population size, distribution, fragmentation, and rate of decline of populations. It is well recognised that species differ in the amount of unique evolutionary history they represent. All else being equal, the loss of an evolutionarily unique species with no close relatives represents a greater loss of biodiversity than the loss of a species whose evolutionary history is, to a larger degree, shared with several closely related species. Therefore, phylogenies can play a role in prioritising species for conservation, if the goal is to maximally conserve biodiversity. Presently, it is unclear whether the geographically restricted genus-group classification in Melanesian Placostylinae is a reasonable reflection of evolutionary history of the group, or an artificial taxonomic construct. Clarification on this matter is of practical importance as there is an opportunity to prioritise and coordinate policy development and conservation effort at the regional scale rather than on a country-by-country basis. Furthermore, phylogenetic analyses based on DNA samples from across the geographic range of genus- and species-group taxa would enable delineation of ESUs and inform conservation plans that seek to ensure adequate representation of genetic diversity both in protected natural area networks and across sites being actively managed. And not least, such evolutionary information would enable a robust taxonomic revision of Placostylinae, with end-point objectives being stabilisation of taxon nomenclature, a taxonomic hierarchy that better reflects evolutionary relationships, greatly advanced understanding of spatial patterns of diversity, and improved diagnostic tools including identification keys. Concluding remarks Terrestrial gastropods are highly successful, second only to arthropods in species diversity. However, these gastropods have the highest recorded modern extinctions of all terrestrial animal groups (Lydeard et al. 2004), reflecting their sensitivity to environmental change. Extinction has been particularly pronounced in land snails endemic to oceanic islands, not least those of the Pacific (e.g. Solem 1976; Kay and Schoenberg-Dole 1991; Bouchet 1998; Abdou and Bouchet 2000; Bouchet and Abdou 2001, 2003; Boyko and Cordeiro 2001; Lydeard et al. 2004; Re´gnier et al. 2009; Zimmermann et al. 2009; Brook 2010; Chiba and Roy 2011; Richling and Bouchet 2013; Sartori et al. 2013). The causes of decline are anthropogenic, but poorly understood. While it is clear that significant components of extinction in island faunas can be attributed to severe habitat loss and invasive mesopredators, there is concern that extinctions are


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ongoing in residual indigenous forests (e.g. Brook 2010; Brook et al. 2010), including those in montane areas considered important biodiversity refugia in island systems otherwise heavily impacted by human activities (Olson et al. 2006, 2010; Schmitt et al. 2009; Woinarski 2010). Much has been written about extinctions and ongoing decline of Pacific Island land snails, but the Placostylinae have largely been neglected. In this paper we have attempted to summarise the situation in respect to these land snails. Many placostyline species have exhibited remarkable persistence in the face of severe habitat fragmentation and degradation. However, extinction debt (Tilman et al. 1994; Triantis et al. 2010) undoubtedly will play out in these modified landscapes unless protected areas are established and indeed protected, and restoration programs reinstate indigenous functional dominance and reconnect isolated remnant forest patches. There is evidence from New Zealand, Lord Howe Island and New Caledonia that Placostylinae on the one hand continue to decline in both range and abundance in degraded landscapes, and on the other respond well (at least in the short term) to ecosystem manipulations that aim to mitigate threatening processes such as predation by invasive mammals. It has yet to be clearly demonstrated, however, that long-term persistence of Placostylinae can be achieved in degraded landscapes that continue to be subject to anthropogenic pressures. In New Zealand, only on uninhabited, pest-free islands do these snails persist in high numbers, and these ‘sanctuaries’ are dependent on biosecurity vigilance. Effective predator control at some mainland sites in New Zealand has locally resulted in high snail densities, at least in the short term – whether these densities can be sustained in the medium to long term remains to be demonstrated. Several Placostylus species in New Caledonia have exhibited remarkable resilience in the face of substantial harvest by people. In Fiji, at least some species of Placostylinae remain common in forests, but others have not been sighted for over a century. Virtually all forest habitats in Fiji have been modified over the centuries through slash-and-burn subsistence gardening, with some clearance for agriculture, and in recent decades many lowland areas have been subject to logging. Over the centuries the forests of Vanuatu and the Solomon Islands have been subject to only low-level anthropogenic disturbances, but in recent decades the situation has become highly dynamic in the lowlands with the advent of industrial-scale logging, forest clearance for plantations and agriculture, pressures from rapidly increasing human populations, and associated ingress of invasive species. The consequences for Placostylinae are largely unknown as there has been little inventory work, but the prospects for these snails in the lowlands looks bleak unless there is concerted effort to curtail ecosystem perturbations. The degree to which the montane areas of Melanesia provide secure refugia for Placostylinae remains to be fully examined, but these areas are not without ongoing influence from humans and invasive species. The forest habitats of Placostylinae in the New Zealand– Melanesian region represent globally significant biodiversity hotspots (Olson and Dinerstein 1998, Allison and Eldredge 1999; Schmitt et al. 2009; Olsen et al. 2010; Woinarski 2010). The snails themselves represent a unique evolutionary history (Breure and Romero 2012) that is diagnostic of the region and of

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such international significance as to demand concerted conservation action. Unfortunately, most knowledge of biodiversity in Melanesia derives from 19th Century expeditionary exploration, and little has been done using modern methods such as quantitative biodiversity assessment and molecular studies of taxon evolution. For Placostylinae the most pressing research issues are the evolutionary relationships across the entire subfamily as a framework for conservation policy and actions, and spatial patterns of diversity in the Solomon Islands and Vanuatu to enable robust assessment of extinction risk. The ongoing establishment and recognition of several national and community-based protected forest areas represents an excellent opportunity with respect to Placostylinae on several fronts, not least the active management of the threats to these snails, and to bring land snails to the fore and inclusion among focal taxa, thus broadening the taxonomic coverage of conservation, especially in Melanesia. Aside from the conservation imperatives, the Placostylinae represent remarkable research opportunities in the areas of evolutionary biology, biodiversity pattern, and anthropogenic history. Gradients of potential interest include: (1) diversity of arboreal snails (rich in the Solomons, intermediate in Vanuatu, Fiji, New Caledonia, poor in New Zealand and Lord Howe Island); (2) native rodent diversity (modest in the Solomon Islands, absent in Vanuatu, Fiji, New Caledonia, New Zealand and Lord Howe Island); (3) period of human occupation (from 30 000 years ago in the Solomon Islands, 3000 years ago in Vanuatu, Fiji, New Caledonia, 1300 years ago in New Zealand; 225 years ago in Lord Howe); (4) severity of landscape change wrought since European contact (severe in New Zealand, moderate in New Caledonia and northern Lord Howe Island, modest in Fiji and Vanuatu, minimal in the Solomon Islands). It remains untested whether the Solomon Islands’ Placostylinae, having evolved in the presence of rodents and thus rodent predation, are more resilient than the rodent-naı¨ve Placostylinae of Vanuatu, Fiji, New Caledonia, Lord Howe Island and New Zealand. Also, it is unclear whether the 3–30 millennia of human occupation of the lowland habitat of Placostylinae in Melanesia has imposed selection forces favouring snail species tolerant or indeed favoured by forest disturbance, as opposed to the situation in New Zealand and especially Lord Howe Island, where human occupation is much more recent. Research on these topics is not merely academic, as information directly relevant to placostyline conservation would accrue, as would greater awareness of these land snails. Acknowledgements We are indebted to Fred Brook, Andrea Booth, Thomas Buckley and Fabrice Brescia for providing information on the conservation status of Placostylinae in New Zealand and New Caledonia, and Fred Brook and two anonymous referees for their constructive comments on earlier versions of this paper.

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