PacificPacific SSciencecience (1989),(1989), vol. 43, 43, no.no. 1 © 19198989 byby UniversityUni versity ofof HawaiiHawaii Press.Press.All Allrights rights reservedreserved Demographic Studies on Hawaii's Endangered Tree Snails: Partulina proxima 1 2 2 MICHAELMICHAEL G.G. HADFIELDHADFIELD AANDND SSTEPHENTEPHEN E. MILLER ABSTRACT: Populations ofthethetree tree snail Partulina proproxima,xima, endemicendemicto higher elevationselevations of Molokai,Molokai, HawaiianHawaiian Islands,Islands, were studiedstudiedfor 3 years.years. AnalysesAnalyses of the data derived from 17 bimonthlybimonthly mark-recapture eventsevents determineddetermined that each tree harborsharbors a small, small, mostlymostl y nonmigratorynonmigratory populationpopulation of 8-26 8-26 snailssnails of which 2-42-4 areare adults; the snails average 4.2 mm long at birth and 21.3 mm long when growth stops;stops; growth isis slow, with maturity reached in 55-7-7 years;years; annual fecundity averages 6.2 6.2 offoffspringspring per adult; and mortality is about 98%98% over the first 4 years years of life. Given the high rate ofjuvenile mortmortality,ality, adult snails must reproducereproduce for at least least 1212 years to replace themselves. From this we calculate a minimum maximalmaximal life-spanlife-span of 18-19 18-19 years.years. We conclude that the current high rate of unexplained juvenileju venile mortmortality,ality, combined withlate late aagege aatt fifirstrst reproduc­ tion and loloww fecundity,fecundity, placplacee thisthis sspeciespecies at veveryry hihighgh riskrisk to any ssortortof perturbatperturbation,ion, particularlparticularlyy any selective predation on adultadults.s. AMONGAMONGTTHEHE MOSTMOSTRAVAGEDRAVAGED BIOTAS in the theworld world and predatorypredatory animals;animals; probablyprobably introducedintroduced isisthat that of the Hawaiian Ha waiian IslandsIslands ((ZimmermanZimmerman pathogens (though(thoughessentially essentially unstudiedunstudied);); 1970).1970). Hawaii'sHawaii's unique,unique, ininsularsular faunafauna aandnd andand,, for a numbernumber of groupsgroups of plants plantsand and floraflora,, once a sshowcasehowcaseof of didiversificationversification animals,animals, sselectiveelectiveharvesting harvesting ((e.g.,e.g.,hardwood hardwood through eevolution,volution, arenow bbetteretter knownknown as trees,trees, thethe nenenene goose).goose). leledgersdgers of extinction.extinction. RecordedRecorded extinctionsextinctions The endemicendemicachatinelline achatinelline tree snails snails of includeinclude 40%40% of endemic birdsbirds(Berger (Berger1970), 1970), Hawaii havehave long been known for ththeireir beau­ uncounteduncounted numbnumbersers of endemic insects insects(e.g., (e.g., tty,y,variety, variety, and gregreatat local evevolutionaryolutionaryradi­ radi­ GGagneagne 1982,1982, Gagne andandHowarth Howarth 1982),1982), and aationtion ((GulickGulick 1905). On theisland island of Oahu,Oahu, probablyprobably 5050%% of the nearly 1000 sspeciespecies of more than 170 varietiesvarietiesof the endemic genus genus terrestrialterrestrial gastropodsgastropods ((KondoKondo1970) 1970) thatthat once AchatinellaAchatinella havehave been dedescribed.scribed. TheThe 30-4030-40 inhabitatedinhabitated thesethese islands.islands. FosbergFo sbergand andHerbst Herbst speciesspeciesrepresented represented byby thesethese forms are now (1975) estimated that 66%66% of Hawaii'sHawaii's nativenative more than 50%50% extinct (Kondo(Kondo1970), 1970), and the plantsplants are rare,rare, endangered,endangered, orextinct. AgentsAgents remainderremainder arearerare rareand and found only in high­ of annihilationannihilation are known to includeincludethe elevation residuesresidues of once widewidespreadspread nativenative following:following: habitathabitat destructiondestruction (clearing(clearing for forestforest.. MembMembersers of the closely closely related genusgenus farming,farming, logginglogging,, and housing;housing; grazinggrazing by Partulina of Molokai,Molokai, Maui,Maui,and and Lanai are introduced mmammals);ammals); introduction of exotic probablyprobably equallyequally devastated,devastated, but theythey have grasses,grasses, sshrubs,hrubs,weeds, weeds, and trees,trees, which out­ not been systematically systematically surveyedsurveyedin many competecompete nativenative plantsplants and prove pro ve inhospitableinho spitable years.years. The PartulinaPartulina speciesspeciesof the island of to native animals; anim als; introductionintroduction ofcompetitorcompetitor Hawaii havehave notnot beenbeen recordedrecorded for 20-3020-30 years,years, andandare are probablyprobably extinct.extinct. TheThe entireentire genusgenus AchatinellaAchatinella isis on the U.S. endangered 1 ManuscriptManuscript acceacceptedpted I May 1988.1988. TThishis paperpaper was presentedpresentedat a symposium symposium entitledentitled "Molluscs" Molluscsas Threat­Threat­ sspeciespecieslist, list, aandndwas was cited iinn1985 1985aass oneof tthehe enedenedSpecies: Species: TheirTheirExploitation Exploitation andand Conservation,"Conservation," 12 momostst ccriticallyritically eendangerednda ngered specspeciesies in the given at at the 19th19thAnnual AnnualMeeting Meetingof the InternationalInternational world bbyy ththee InternationalInternational UnionUnion for the Con­ MalacologicalMalacological UnionUnion (Unitas(UnitasMalacologia), Malacologia),Edinburgh, Edinburgh, servationservation of NatureNature andand Natural ResourcesResources Scotland,Scotland, SeptemberSeptem ber1986. 1986. ((AnonymousAnonymous1985). 1985). 2 UniversityUniversity of Hawaii, Hawaii, KewaloKewaloMarine MarineLaboratory Laborat ory ananddDepartment Department of ZZoology,oology, 41 AAhuihui StreetStreet,, Honolulu,Honolulu, Until recently,recently, sscientificcientific knowledge of the the HawaiiHawa ii 96896813.13. achatinelline snailssnailswas wasvirtually virtuallyconfined confined to 2 PACIFIC SCIENCE,SCIENCE, Volume 43, January 1989 taxonomic descriptions of shells and, to a ent analyses were obtained by field mark­ small extent, radulae.radulae. Although a number of recapture techniques on members ofthe acha­ workers described soft-part anatomy, they did tinelline species Partulina proxima (Figure 1)I) so mainly with taxonomic questions inmind on the island of Molokai.Molokai. TheseThese data provide (e.g(e.g.,., Cooke and Kondo 1960). Thetypes of insights into the species' life history pattern,pattern, trees inhabited by the snails and the epiphytic the possible evolutionary history of this pat­ fungal dietof the snails were briefly described tern,tern, and the role ofthe pattern in the decline in older works, but only recently have major of local populations. Such information is es­ life history characteristics become knownknown.. sential toan understanding of extinctionextinctionin Only three papers, all completed in this de­ this fascinating molluscan group and for dede­­ cadecade,, discuss growthgrowth,, fecundity, or other de­ vising means to protect (or even replenish) mographic characteristics of any achatinelline remaining species. Similar preliminary data species (Hadfield 19861986,, Hadfield and Moun­ have been presented for two other species tain1980, Severns 1981). (Hadfield 19861986,, Hadfield and Mountain 1980). Extinction, as an observable processprocess,, has two major facets:causal agents(i.e., (i.e., what is killing the organisms?) and specific vulner­ MATERIALSMATERIALS AND METHODS ability factors (i.e., why do some organisms dieout while others survive?). For the acha­ Partulina proxima populations were studied tinelline snails, much has been written about in three small o'hia o'hia trees (Metrosideros poly­ the destructive factors (summarized by Had­ morpha) in a wet forest at an elevation of field 1986), but the basisof their vulnerability about 1200 m. m. The site lies in The Nature isless clear. Certainly, theyshare the sensitivi­ Conservancy's Kamakou Preserve, nearthe ty known to characterize many insular biotasbiotas ridgeline of the island of Molokai. Each ofthe evolved in the absence of predators and her­ study trees, trees, labeled X-IX-I,, X-IIX-II,, and S (Figure bivores (Carlquist 1970).1970).TheThe data for the pres- 2), is about 2 m tall and 2-3 2-3 m in diameter. FIGUREFIGURE I. PartulinaPartulina proxima. a, a, adult; b, juvenile,juvenile, about 10 monthmonthss old.old. ScaleScale is the same for both photographs. (Photographs courtesy of Peter C. C. Galloway.)Galloway.) M gt! rgggt.§## I g , tW.li$n'tfflibtMlffflffiftit#~m*mU"i MM•m f#IIWt#¥% $4 # $6## #@, :o.WifUffiQ 4&"I&I"'4Ino 4 $IS,. Demographic Studies of Partulina proximaproxima-HADFIELD-HADFIELD AND MILLER 3 FIGURE 2. Study trees (Metrosideros polymorpha)polymorpha).. a,a, tree X-I; b,b, tree S.Person in photographs is about 160160emcm tall. (Photographs courtesy of E. E. Jane Albert.) 't" . 4 PACIFIC SCIENCE, Volume 43, January 1989 Trees X-I and X-II are about 2 m apart; tree at birth was determined by taking the average S is about 800 m away.While the forestin this size ofall snails whose length was less than 44.6.6 area is dominated by native treestrees,, with M. mm when first observed.observed. Size at maturity was polymorpha and Cheirodendron sp. the most taken as the average length of shells with a common, there is an added component of in­ thickened apertural lipor callus. (3) Growth troduced species, including Monterey cypress rate was analyzed by a variety of techniques and New Zealand flax. The native snails have including the von Bertelanffy model and a never