PacificPacific SSciencecience (19(1989),89), vol. 4343,, no.no. 1 © 19198989 byby UniversityUni versity ooff HawaHawaiiii Press.Press. AAllll rrightsights 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 IIslands,slands, were sstudiedtudiedfor 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 snailsaverage 4.2mm long at birth and 21.3 mm longwhen 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 first4 yearyearss 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 iissthat 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 numbenumberr 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 exextinctionstinctions The endemicendemicachatinelline achatinelline tree snails snails of includincludee 4040%% of endemic birdsbirds(Berger (Berger1970), 1970), Hawaii havehave long been known for ththeireir beau­ uncounteduncounted numbnumbersers of endemicinsects 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 AAchatinellachatinella havehave been dedescribed.scribed. TheThe 30-4030-40 inhabitatedinhabitated thesethese islands.islands. FosbergFo sberg aandndHerbst Herbst speciesspeciesrepresented represented byby thesethese forms arenow (1975) estimated that 66%66% of Hawaii'sHawaii's nativenative more than 5050%% extinct (Kondo(Kondo1970), 1970), and the plantsplants are rare,rare, endangered,endangered, orextinct. AgentsAgents remainderremainder arearerare rare aandnd found only in high­ of annihilationannihilation are known to includeincludethe elevation residuesresidues of once widewidespreadspread nativenative following:following: habitathabitat destructiondestruction (cle(clearingaring for forestforest.. MembMembersers of the closelcloselyy related genusgenus farmingfarming,, logginglogging,, and housing;housing; grazinggrazing by Partulina of Molokai,Molokai, Maui,Maui, aandnd 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 PaPartulinartulina speciesspeciesof the island of to native animals; anim als; introductionintroduction ofcompetitorcompetitor Hawaii havehave notnot beenbeen recordedrecorded for 20-3020-30 yyears,ears, aandnd araree probablprobablyy eextinct.xtinct. ThThee entirentiree ggenusenus AchatinellaAchatinella iiss on the U.S. endangered 1 ManuscriptManuscript acceacceptedpted I May 1988.1988. TThishis paperpaper was prpresentedesentedat a symsymposiumposium entitledentitled "Molluscs" Molluscsas Threat­Threat­ sspeciespecieslist, list, aandndwas was cited iinn1985 1985aass one of 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 aandnd Natural ResourcesResources Scotland,Scotland, SeptemberSeptem ber1986. 1986. ((AnonymousAnonymous1985). 1985). 2 UniversityUniversity of HawaiiHawaii,, KKewaloewalo MaMarinerineLaboratory Laborat ory ananddDepartment Department of ZZoology,oology, 41 AAhuihui StreetStreet,, Honolulu,Honolulu, Until recently,recently, sscientificcientific knowledge of the the HawaHawaiiii 96896813.13. achatinelline ssnailsnailswas was vivirtuallyrtuallyconfined confined to 2 PACIFIC SCIENCESCIENCE,, 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 in mind 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 tain 1980, 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, muchhas 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, they share the sensitivi­ Conservancy's Kamakou Preserve, near the ty known to characterize many insular biotasbiotas ridgelineof theisland 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 lip or 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 Bertelanffymodel anda never been encountered on either ofthe latter,latter, series of regression analyses including linear, although they are seen on other native shrubs logarithmiclogarithmic,, exponential, and allometric in the area, area , including species of Coprosma and models and curvilinear regressionsup to the Wikstroemia. fourth power (Sokal and Rohlf 1981).1981). None The study site was visited 17 times at ap­ ofthese resulted in predictions consistent with proximately 2-month intervals betweenNo­ empirical knowledge of the snails. Thisis un­ vember1983 and July 19861986.. On each visit, doubtedly due both to the parameter mea­ each of the study trees was visually searched sured (shelllength is probably not a good by four workers for at least 1 hr, and all snails indicator of growth in animal mass) andto the were carefully removed and placed in screen­ extremelyhigh variance in growth rate in all ed,ed, lidded boxes containing moistened filter size categories (see Figure 4). The most satis­ paper. Each snail wasthen examined to deter­ factory growth curve (rate versus size) was mine whether it had been marked previously, obtained by first calculating growth rate (mml(mrn / and if not, an individual code number was day) and midsize for all intervals available for assigned to thesnail. Numbers were written all growing snails. snails. Then the growth rate data onthe snails' shellswith india ink and coated were averaged over various size intervals until with a fast-drying,fast-drying, waterproof lacquer. For a pattern emerged (based on large enough very small shellsshells,, where applying a number samples to be reliable) that showed a rate-size would have beennearly impossibleimpossible,, codes relationship consistent with the distribution were applied with small dots of fast-drying of all data in a scatter diagram. The animal paint (Uni-Paint Markers, manufactured by size data were then converted to ages, and FaberCastell®).FaberCastell®). After marking,marking, lengths and age-frequencyage-frequency histograms were constructed. widths ofall animals were measured with pre­ (4) Fecundities were determined for thetwo cision calipers to 0.01 mm. mm. SubsequentlySubsequently,, the trees X-I and X-II together andfor tree S. snails were returned to the treesfrom which These were calculated by assuming that only they were collected. Small snails crawl readily snails with a thickened shell lip were repro­ and werereplaced directly on moistened ductively mature (Neal 1928). All snails with leaves orlimbs. Larger snails that were crawl­ shells ofless than 7mm when first observed ing were also put onto the trees, but deeply were assumed to have been born into the pop­ retracted snails were placed, together with ulation within the year under consideration. moistened leaves, in screen-bottomed, plastic This number divided by the average number cups that were tackeddirectly to a trunk. All ofmature snailsin the treeis the annual indi­ such snails returned tothe tree during the first vidual fecundity. Thefecundity numbers were night following collection. then averaged over all possible successive 12­ The mark-recapture data were analyzed to month intervals (16 total) of the study. determine population size and survivorship in Finally, survivorships were analyzed by di­ each tree; sizesat birth and maturity; snail viding the populations into two groupsgroups:: snails growth rate; size-age size-age relationships and age­ lesslessthenthen 18.1 mm long and snails 18.1 mm and frequency distributions in the populations; longer. Because mortality is very lowin adult and fecundity. The methods used for eachof Partulina proxima, it was analyzed both by these analyses were as followsfollows:: (1) Population the Manly-Parr and Jolly methods and by densitieswere determined for each tree using empirical examination of the datadata.. In the em­ the Manly-Parr and Jolly methods for pirical analysis, all large snails that disap­ multiple-recapture data (Begon 1979). 1979).(2)(2) Size peared from the study trees for 6 months or

UN9S 4 a c 'A. Demographic StudStudiesies of Partulina proxima-HADFIELDproxima-HADFIELD AND MILLERMILLER 5

longer were considered to be dead.While such the site; snail S2was seen on all but one occaocca­­ ddisappearancesisappearances are ""mortalities"mortalities" in termsof sionsion;; and ssnailsnails XXl 1 and X17X 17were seen on all the population,population, they may represent emigra­ but two visits. Afew large snails were seen tion. Snails seen only only once or twice during the once, or perhaps twicetwice,, and then never againagain.. study were considered to be "transients"transients"" and We assume that such snails were "trans"transient"ient" not counted as part ofthe populations. Juve­ animals living in amuch broader area than nile mortality rates were calculated from most large snailssnails,, which tend to remain loyal the ageage-frequency-frequency distributions and by the to a single tree. Because all three study trees Manly-Parr and Jolly methods applied only are isolated by surrounding grassy areas and to recapture data from snails less than 18.01 do not have branches that touch any other mm long. treetree,, the transient snails must cross ground covered with deep grass when moving from tree to treetree.. When a snail had been present in oneof the study trees forlong periods oftime RESULTS and then vanished, we considered it tobe a A total of160snails160 snails was labeled in the study result ofmortalitymortality.. However, on only two oc­ trees between November 1983 and July 1986; casions didwe find dead shells on the ground,ground, 36 were seen in tree X-I, X-I , 28 in X-II, and 96 in although a careful search was made for such S.These These snails accounted for 296 recapture shells on each visit. Their thinness,thinness, perhaps events on one or more of the last16 visits to coupled with wet and acid soil conditionsconditions,, the site. However, 68 snailssnails,, constituting 4343%% may lead to rapid disintegration of the shells. of the snails observed, were seen ononly one Itis also possible that wild pigs, pigs, which are ververyy occasion and thus donot contribute to extrap­ abundant in the study area, eat snails or emp­ olations such as growth rate. Forty snails ty shells when encountered on the ground.ground. (25%)(25%) were observed on only two occasions. (Calcium may be at a premium in these high ThusThus,, 8686%% [(296 - 40) ...;--;-- 296]of therecap­ forested areas.) ture eventswere based on threeor more obser­ Undoubtedly,Undoubtedly, the number of snails fluctu­ vations of 52 snails. These data provide the ates in each of the trees. The major cause of basis for all the life history parameters deter­ the fluctuation is the birth and disappearance minedbelow. below. ofjuvenile snails.While large numbers ofnew small snails were observed on some occasions 1.Population Densities and none on others,others, no seasonal or annual periodicity was detected in the birth ofyoung The number of snails observed in each tree snails, and birth clearly occurs throughout the varied among visits from 3 to11 IIfor tree X-I, X-I, year. 2 to 7 for tree X-II, and 10to 22 for tree S, S, with averages of 5.65.6,, 44.8,.8, and 16.8, 16.8, respectively. 2. Sizes at Birth and Maturity Using the Manly-ParrManly-Parr method for estimating population numbers from multiple mark­mark­ Birth size in Partulina proxima,proxima, calculated recapture data,data, we determined the average as the mean size of all snails (from all trees) numbenumberr of snailsper tree to be 77.8.8 (± 33.8).8) for under 44.6.6 mmlong atfirst capturecapture,, is 44.2.2 ± tree X-IX-I,, 9.1 (±3.8) for tree X-II,X-II, and 26.5 00.2.2 mm (n = 25). The smallest shells seen were (± 5.6) for tree S. Estimates by the Jolly 3.8 mm long. It is possible that some snails are method were 7.1 (±3.8)(±3.8),, 8.5 (±3.0)(±3.0),, and born at sizes larger than 44.5.5 mm, but captive 27.1 (±6.0)(±6.0),, respectively.respectively. culture will be necesnecessarysary to determine this. All the trees were characterized by constant constant Mean birth size was slightlslightlyy different when the numbers of reproductive adults (2 in each of two groups of trees were considered sepa­ trees X-I and X-IIX-II,, and 4 in tree S)S),, and the rately: for the X treestrees,, it was 4.1 ± 0.2 mm same adult snailswere seen reperepeatedlyatedly in each (n = 14)and for the S tree, tree, 4.4 ± 0.1 mm (n = tree for many successive visits. For exampleexample,, 11).11). Thesedifferences are significant atthe snailX7 was seen intree X-II on every visit to level of P > 0.05,0.05, but notat P > 0.010.01 (t test). 6 PACIFICPACI FI C SSCIENCE,CIENCE, Volume 43, 43, JanuaryJanu ary 19891989

ThTheecombined combined avaverageerage birth sizsizee wasutilized utilized p < < 0.05).0.05). SiSizeszes of lippedshells variedvaried to calculate yearyear groups (below),(below), becauseof widely,widely, ranging from 19.7 19.7 to 24.4 mm in the extremely extremely small samplesample sizes for some size length.length . classesclasses thatwould have have resulted from treating the two groups of trees sseparately.eparately. 33.. SiSize-Frequencyze-Frequency DistributionsDistributions Average ssizeizeat maturitymaturity was taken to be the meanlength of all shellshellss with a thickened shell Size distributiondistributionss ofofthethe ssnailsnailsin the X trees trees lip.lip. The formation of this distinctive featurefeature and the Stree were determined for 2-mm ssizeize signalssignalsthe end of shell growth and has been classesclasses bbyy averaging the numbers of snsnailsails previously noted to be anecessary necessary charactercharacter­­ found on eaeachch of the17 visitsvisitsto the sstudytudy istic of of reproducing snails(Neal (Neal 1928).1928). Due to area.area. The resultant histogramshistograms (Figure3) aptlyaptly the endangered statustatuss of aallll achatinellines, our demonstratedemonstrate the preponderance of small young sstudiestudieshave been entirelynonsacrificial, nonsacrificial, and snails,snails, the paucity of snailsin the midsizes we have not performed the numerous dissec­dissec­ (12-18(12-18 mm),mm), aandndthe larger numbersnumbers of large tions that would be necessary to verify the snails.snails.The patterns are similar for thethetwo relationshipsrelationships among shell ssize,ize, shell liplip,, and ssites,ites,as can can be seen in Figures 3a and 3b. MoMostst reproductive state.state . The average size of all of the snailssnailsin the smallest size class were lipped sheshellslls we obsobservederved was 21.3 21.3 ± 1.3mm newly observed observed on each visitvisit,, and momostst werweree ((nn = 17).17). As was the case for ssizeize at birthbirth,, the seen only onceonce,, indicating the frequency frequen cy of aaverageverage sizes ofoflippedlipped shells differed between addition of small snails to the populations.populations. tthehe twotree groupgroups:s: for the X treestrees,, it wwasas Large lipped shellsshells werewerefound in more than 20.9 ± 0.8 mm (n = 10)and for the S tree, tree, three 2-mm 2-mm sizesizeclasses classes (Figure 3),3), indicating a 21.921.9 ± 1.61.6 mm (n = 7)7).. The difference difference be­ significantsignificant variance in the size size at which which matu­matu­ tweentween these means means is not significantsignificant (t tetest;st; rityrity (and the the cessationcessation ofshell growth) growth) occurs.occurs.

6 6

5 5

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~ IIII() IIII() IIILO IIII() IIILO IIII()IIII() IIII() 0 ~ IIII()IIII() IIII() IIILO IIII() IIILO IIILO I()III 0 0 0 Cl~ 0 0 0 0 Cl~ - 0 0 Cl~ 0 0 0 Cl0 Cl~ - <0to ,..:~ ai - ,.; .0to ,..:~ ai - N <0to ,..:~ ai - ,.; .0to ,..:~ mai - N v - cc v '" '"A '" '"•A a SSizeize (mm) b SiSizeze ((mm)mm)

FIGUREF IGURE 33.. Size-frequencySize- frequency distributiondistributionof of PartulinaPartulina pproxima.roxima. aa,, trtreesees X-X-II aandndX-II X-II ccombined;ombined; b, treetree SS.. SizesSizes arearc expressedexpressed as classclass marksmark s forfor 2-m2-mmm sisizeze classesclasses;; bbarar llengthsengths rrepresentepresent tthehe mean nnumberumber of ssnailsnails cacapturedptured in eaceachh ssizeize clclassass duduringring 1717 visivisitsts to ththee ststudyudy sisite.te. StippledStippled barsbars representrepresent mature,mature,nongrowing nongrowing snailssnails (those(those withwith lippedlipped shells).shells).

KtilIldl&t21IllfJ1l&,' b&§ DemographicDemographic StudiesStudies of PartulinaPartulinaproxima-HADFIELDproxima-HADFIELD ANDAND MILMILLERLER 7

Needless to say, say, this currently currently presents an inin­­ As rate decreases, decreases, so does variance, variance, and largest largest surmountablesurmountable problemproblem fordetermining determining the shells,shells, as previouslypreviously stated,stated, do not grow.grow . age of ssnailsnails with llippedipped shells. TThehehigh highgrowth growth rate variance, coupledcoupled with the low number ofmeasurements measurements for the mucmuchh more rarelyrarely occoccurringurring midsizedmidsized 4.4. GroGrowthwth RateRate ssnails,nails, prepresentedsented considerableconsiderable difficultyin All repeat measurementsmeasurements for aallll ssnailsnails were devising a growth curvecurve for the Partulina trtranslatedanslated into growth rates bbyy determining proxima populations studiedstudied.. Simple exami­ the amount grown by each ssnailnail duringduring eacheach nation of mean growth ratesrates acrossacro ss all 2-mm2-mm intervalinterval and didividingviding it bythe number ofdays da ys size classessuggested that snails mature after that had elapsed between measurementsmeasurements..TheThesese reaching 6 years years of age (Table (Table1, I, Figure 3)3).. rates (mm x 10-10- 3 day-l)day") were then pplottedlotted Entering allthe growth data into the calcula­ calcula­ against tthehe midsizesmidsizes of of the snaisnailsls during the tionstions for the von vonBertelanffy Bertelanffy growth modemodell intervalsintervals for which rate was determined.determined. TheThe resulted in a predictionprediction of maturitymaturity (i.e.,(i.e., the resultingresulting scatter diagram (Figure 4) presents a attainment of asymptotic shellshelllength) length)at 33 rough picturepicture of thethe pattern of change iinn years-clearlyyears-clearly a false false prediction.prediction. TheThe seriesseriesof growth rate as snasnailsils growgrow.. Variance in growth regression modemodelsls tested on all all data for grow­ grow­ rate is extremelyextremely high across all size classes, classes, ing shells (omitting lipped shells) pproducedroduced 2 butbut is greatest inthe smaller classes classes (4-12(4- 12mm).mm). equationequationss with a best fit of 1'r2 = 0.26.0.26.

24 22 o 20 o 0 o 11'IIt) 18 I o o 16 aD A ,...... ~ o A A 14 o A 12 o o 10 o 8 AO o 6 A 0 0000 0 AA 4 c:fJ AAA A fi¥:A A °A~ 2 e~AAA o

o 2 4 6 8 10 12 14 16 18 20 22 24 26 Midlength (mm)(rnrn)

FIGURE 44.. Growth rate as a function ofaanimalnimal sisizeze iinn PartulinaPartulina proxima.proxima. Growth ratesrates for aallll rerecapturecapture intintervalservals of growing snaisnailsls werweree ccalculatedalculated andplotted plotted agagainstainst midlmidlengthength ooff thethe snailsnail durduringing the interintervalval (0,CO, X trtrees,ees, n = 80;80; 6,6., S tree,tree, n = 128).128). 8 PACIFIC SCIENCESCIENCE,, Volume 443,3, JJanuaryanuary 19198989

TABLTABLEE 1I

SIZE-GROWTHSIZE-GROWTH RATERA TE RELATIONSHIPS ININ Partulina proxima

1-mmI-mm SISIZEZECCLASSESLASSES 2-mm SIZESIZE CLASSES ADJUSTED SISIZEZECCLASSES'LASSES*

SIZESIZE ((mm)mm) n XX-RATE- RATE SSDD SSIZEIZE ((mm)mm) n X-X-RATERATE SD SIZESIZE (mm) n X-RATEX -RATE SD

<5.0< 5.0 1212 7.597.59 4.46 <6.0< 6.0 65 7.41 3.69 3.69 <6<6.0.0 6655 7.413.69 3.69 5.0-5.0- 55.9.9 5533 77.37.37 33.54.54 6.0-6.0- 77.9.9 5544 8.098.09 3.43 6.0-6.0- 7.97.9 5454 8.098.09 3.43 6.0-6.0- 6.96.9 31 8.058.05 33.56.568.0- 8.0- 99.9.9 2222 10.415.22 5.228.0- 8.0- 99.9.9 2222 10.41 5.22 77.0-.0- 7.923 8.28.200 33.32.32 1010.0-11.9.0-11.9 II11 99.07.07 33.31.31 1010.0-16.9.0-16.9 221110.33 10.33 3.373.37 8.0-8.0- 88.9.9 II11 11.481\.48 5.47 12.0-13.9 12.0-13.9 5 10.10.21212.08 2.08 1717.0-18.9.0-18.9 13 66.17.17 44.01.01 99.0-.0- 9.9.99 11 9.31 44.97.97 14.0-15.914.0-15.9 3 13.47 2.31 2.31 19.0-19.919.0-19.9 12 33.23.23 22.67.67 10.010.0-10.9-10.9 4 8.838.830.97 0.97 16.0-17.916.0-17.9 9 66.83.83 4.224.22 20.020.0-20.9-20.9 18182.68 2.682.23 2.23 11.011.0-11.9-1 \.9 7 9.21 4.21 1818.0-19.9.0-19.9 18 4.46 33.73.73 2\.021.0-21.9-2\.9 9 1.44 1.34 12.0-12.912.0-12.9 3 10.2810.28 2.542.5420.0-21.9 20.0- 21.9 27 22.27.27 22.04.04 1313.0-13.9.0-13.9 2 10.12 22.09.09 1414.0-14.9.0-14.9 2 12.8012.80 22.83.83 1515.0-15.9.0-15.9 1 1414.80.80 1616.0-16.9.0-16.9 2 112.902.90 55.37.37 1717.0-17.9.0-17.9 7 55.09.09 1.71.766 118.0-18.98.0-18.9 6 66.92.92 44.57.57 19.019.0-19.9-19.9 12 33.23.232.67 2.67 2020.0-20.9.0-20.9 11882.68 2.68 2.23 21.021.0-21.9-21.9 9 1.44 1.34

NOTE:NOTE: ·nn = number ofof aanimalsnimals eexamined;xamined ; x raterate = meanmean ggrowthrowthrate rate ooff animalsanimalswith midsizes midsizes in the correspondingcorresponding sizesizerange, range, measuredmeasured as mm x 1010-- 3 day-I;day- I; SD = standardstandard dedeviation.viation. *SeeSeetext text ffororexplanation. explanation.

Because of the poor fit of the models de­ de­ Size Classes".Classes". These size-rate size-rate relationships scribed aboveabove,, a more empirical approach was were then used to calculate size limits for yearyear taken. Data were first tabulated as aaverageverage classes,classes, assuming a birth size size of 4.24.2 mmmm.. The growth rate per lI-mm-mrn ssizeize class (Table 1). reresultingsulting year clasclass-sizes- size data are presented in Sample sisizeszes were aass lowlow as n = 1 forone TableTable 22.. When conconvertedverted to a raterate curcurve,ve, the of these (15(15.0-15.9.0-15.9 mm)mm) and n = 2 for three data take the the form presented in Figure 5,5, a others in the midsize range, and rates were curve that appears to agree well with the dis­ dis­ highly variablevariablebetween the 9- 9- and 15-mm I5-mm ssizeize tribution of data shown in Figure 44.. classes. DataData were then tabulated as rate per2­ 2­ Another empirical test of the conclusionconclusionss mm size class andreexamined (Table1). 1). While drawn above comes from exexaminingamining the trends began to emerge, emerge, sample sizes were still growth curves for individual snails that have quite low for some groups and consistent trends were still unclear. From the first tab­ TABLETA BLE 2 ulation,ulation, it was deduced that growth rate SIZE-YEARS IZE- YEAR CLCLASSASS RELRELATIONSHIPSATIONSHIPS IINN PartulinaPartulina pproximaroxima dropped significantly between sizesizess of 16and 18 mm and that snailssnailsin the midrangemidrange of AGEAGE (yr) YEAYEARR CLASS SIZESIZERANGE RANGE (mm)(mm) approximatelyapproximately 10-17 mm were growing at about the same rate. rate . Thus,Thus, a final final tabulation 0-10-1 0 4.2-4.2- 77.0.0 was carried out by combining size classes with 1-21-2 1 7.1-7.1- 99.6.6 was carried out by combining size classes with 2-32-3 2 9.7-13.19.7- 13.1 similar growth ratesrates and ssplittingplittingthe 16­ 3-43- 4 3 13.2-16.913.2-16.9 18-mmI8-mm class to reflect the significant change in 4-54-5 4 17.0-19.017.0-19.0 rate that occurred within this class. class. These new 5-65- 6 5 19.119.1-20.1-20.1 size categories were large enough to provide 6-76-7 6 20.2-21.020.2-21.0 7-7-88 7 21.1-21.521.1-21.5 reliable means and variances. This final tabu­tabu­ >8 >21.5> 2 \.5 lation is shownshownin Table 1 under "Adjusted" Adjusted DemographicDemographic StStudiesudies ooff PPartulinaartulina pproxima-HADFIELDroxima- HADFIELD AND MIMILLERLLER 9

16

14

~,~ , / \ /\ / \ 12 I\ I\ ,... I\I \ ';""» /' <, «IctI " "'C"'0 b 10 x E E 8 '-J~

Q) ...+' «IctI a:c:: .c:..J::. 6 ...+' ~ 0 '- C>(!) 4

2

O+----r----.------r---....,..-=--:l...-,O-+-----r----.------r---....,...-=-l.....-., o 5 10 15 20 25 Length (mm)

FIGUREF IGURE 55.. HypotheticalHypothetical growth raratete ccurveurve fforor PartulinaPartulina proxima.prox ima. RatesRatesare aretaken taken fromfromTable Ta ble I. "A"AdjusteddjustedSize Size ClassesClasses."." TToooo fewfew growth rratesateswere aavailablevailable forfor aanimalsnimals bebetweentween 10aandnd 1166 mm long long toto bebecertain certain ofthethe sshapehapeof ththee curvecurvein thisthisrange. range. been remeasured a sufficient sufficient numbernumber of times growgrowthth rate that even individual snails demdem­­ to show basic growth trends.trends. A series of such onstrate over timtime,e, regardleregardlessss of ssize.ize. curvescurves iiss presented in Figure 66.. The increaincreasese in sslopelope of the ccurvesurves from small to midsimidsizeze iiss 5. AAge-Frequencyge-Frequency DistributionDistribution and aapparentpparent ((notenoteparticularly particularly ssnailnail X29X29),), aass iiss SuSurvivorshiprvivorship the decrdecreaseease in sslopelope as larger sisizeze isis aachievedchieved ((e.g.,e.g., snsnailail X19). The curvefor ssnailnail S48 clearly Age-frequencyAge- frequenc y histogramshistograms(Figure (Figure7) 7) were demondemonstratesstrates the confounding variance in mademade bybysorting sortingthe capture data into the ssizeize 10 PACIFIC SCIENCE, Volume 4343,, JanuarJanuaryy 19891989

22 517 55

20 ~_-""""'-'X 19 ~X83 18

16 X57

14 'E' 59 g~ 12 ..c of-0+- 0)0> 10 Cc ~ 8 548

6

4

2

0 2 3 45 6 7 8 9 10 1111 12 13 1144 15 16 17 18 SiteVisit Visit (2-month intervals)intervals)

FIFIGUREGURE 66.. Growth curvescurves for 16 16 markedmarked snails.snails. CodeCode numbersnumb ers on eeachach line are thothosese uusedsed in the mmarkingarking studiestudies.s. The firstfirst vivisitsit occoccurredurred in NovemberNovember 19198383 aandnd tthehe lalastst ((numbernumber 1717)) in JulJulyy 191986.86. categories presented in TableTable 22.. WhileWhile these aandnd 0.19for the S treetree;; and resresultsults by the Jolly histograms show the same trends as the size­ size­ method werewere 00.34.34 and 00.19,.19, respectivelyrespectively.. As frequency analyses (Figure 3),3), they also also indi­indi­ snaisnailsls enter the largest size classes, mortality cate the age aatt whichwhich snails probablyprobably mature­mature­ drops off sharply, resultingresulting in a "pi"pile-up"le-up" of some after reachingreaching5 years of age, but but most animalsanimalsin in the largerlargersize classes, particuparticularlylarly afterafter reachingreaching 7 years of ageage!! among mature lipped snaisnails.ls. The age-frequency age-frequency histograms also dem­ AAnnualnnual survivorship of snails largerlarger than onstrate the great loss of smallsmallsnails snails from 1717.1.1mm was determined by several several tech­ each of the study study sites.sites. In tree S (Figure 7b)7b),, niques.niques. Empirical examinatexaminationion ofofthethe 2.8 years the average number ofsnails observedin year year of recapture data showed a total of 14 adults class 3 (0.18) (0.18) is less than 2%2% of that in year observedobserved in aallll the study trees combined (4 class 0 (7.65), (7.65), indicating a mortalitymortality of 98%98% additional snails were coconsiderednsidered transienttransientss between birth andand 4 years of ageage..SSimilarimilarcal­ andwere not counted). OfOf the14 adultsadults,, 4 culationsculations from the ageage-frequency-frequency data for the (28.6(28.6%)%) disappeareddisappeared for periods long enough X trees indicate a mortality of about 92%92% to be considered dead. Survivorship of 0.714 0.714 between birth and thebeginning of the 4th over 2.8 2.8 years equals an annual survivorship year. When annuaannuall survivorship of allall snails of0.887. 0.887. Annual survivorship of snailssnailslarger larger under 18.1 mm was calculated, calculated , resultsresults byby tthehe than 1188mm was an unrealistic 1.1631.163 when Manly-ParrManly-Parr method were 0.32for the X trees calculated by the Manly-Manly-ParrParr multiple recaprecap-- Demographic StudieStudiess of Partulina proxima-HADFIELDproxima- HADFIELD AND MILLMILLERER 11II

8

7

6 6

~ 5 5 U) ...... '" 'iii0ii) 5 5 ...Co. CI>Q) ...Co. 0.Q. CI>Q) 0.Q. ...Co. 4 CI>Q) 4 ... .0.J:l CI>Q) E .0.J:l :::> E :::> Z Z <::<= «l <::<= CI>Q) 3 «l 3 ~ CI>Q) ~

2 2

o 5 6 >6 o 2 a Year Class b Year CClasslass

FIGURE 77.. Age-frequencyAge-frequency distributiondistribution for populationspopulations ofPartulina proxima.proxima. a, treetreess X-IX-I and XX-II-II combinedcombined;; b,b, tree SS.. AverAverageage numbers per visit were tabulated by age accaccordingording to size classes shown in TTableable 2.Stippled bars represent maturemature,, nongrowing snasnailsils ((thosethose with lippedshells). ture analysis and 0.8540.854 by the Jolly method.method. fromfrom the age-size age-size relationshipsrelationships described The average of aallll three estimates is 0.968, 0.968, above) and and were assumed to be the offspring a figure not inconsistentinconsistentwith our numerous of co-occurring co-occurring adults. As mentioned previ­ repeat observationsobservations of most largelarge Partulina ously,ously, the average number of matmatureure snailssnails proximaoproxima. Thus,Thus,juvenilejuveni le mortality is very highhigh,, (those with lippedlippedshells) was 4 in tree Sand 4 a trend that breaks abruptly when snails in trees XX-I-I and X-II combinedcombined.. ThThee number achieve a size of aboutabo ut 18 mmmm.. At tthishis pointpoint of newborn snaisnailsls recorded per year inin the the annual probabilityprobability of survivorship be­ study treesvaried between16 and 25in the X comes very hhigh.igh. trees and from 23 to 33 in the S tree.Annual Ann ual fecunditiesfecundities per adultadult snail,snail, calculated by aver­ aging themean number ofoffspring per adult 66.. Fecundity from all possible successive 12-month interinter­­ All newlnewlyy found snails less than 77.0.0 mm valsvals (i.e., 1-6,2-7,3-8,1- 6, 2- 7, 3- 8, etc.),etc.), were 5.20 (±0(±0.6).6) longlong belong to the first year class (determined in theX trees and7.14 (±(±0.8)0.8) in tthehe S tree

._.._" ...... ~ "-~ . 12 PACIFICPACI FIC SCIENCE,SCIENCE, Volume 43, 43, JanuaryJanu ary 1989

TABLE 3

ANNUALA NNUAL FECUNDITYF ECUNDITY OF Partulina prproximaoxima

X TREES S TREE ALLALL

SITESITEVISIT VISIT MEMEANAN NNO.O. OF TOTTOTALAL NONO.. MEAN BIRTHSBffiTHS// MEMEANANNNO.O. OF TOTOTALTAL NO.NO. MEANMEAN BffiTHS/BIRTHS/ MEANMEANBffiTHS/ BIRTHS/ INTERVALINTERVAL ADULTSADULTSNEWBORN NEW BORN ADULT/YRADULT/ YR ADULTSADU LTS NEWBORNNEW BORN ADULT/YRADULT/YR ADULT/YRADULT /YR

1-61-6 4.174.17 24 5.765.76 3.833.83 2233 66.00.00 55.87.87 2-72-7 4.174.17 24 5.76 5.76 4.174.17 24 5.76 5.755.75 3-83- 8 4.17 24 55.76.76 4.17 26 66.24.24 55.99.99 44-9-9 4.174.17 25 6.00 6.00 4.004.00 26 6.50 6.24 5-105-10 44.00.00 22 55.50.50 44.00.00 27 66.75.75 66.13.13 66-11-11 44.00.00 19 44.75.75 4.004.00 28 7.00 5.87 7-127-12 4.004.00 19 44.75.75 44.00.00 28 77.00.00 55.87.87 8-8-1313 3.83 20 55.22.22 4.004.00 3333 8.258.25 6.776.77 9-149-14 3.67 20 5.45 4.00 4.00 32 88.00.00 66.78.78 1010-15-15 4.64 17 44.64.64 4.17 33 7.92 6.386.38 11-1611- 16 3.673.67 17 4.64 4.64 4.334.33 33 7.617.61 6.256.25 12-1712-17 33.83.83 16 44.17.17 4.174.17 32 7.92 66.00.00

Mean (±SD)(± SD) 5.20±0.65.20±0.6 7.14±0.87.14±0.8 6 6.16±0.3.16±0.3

(Table(Table 3).3). Average annual fecundity among survisurvivorshipvorship rate of 0.27,0.27, extrapolated from all adult snails was 66.16.16 (±0.3). the age-frequency age-frequency data forfor the S tree, tree, yields a predictionpredictionfor reproductivereproductive life of 13.8 years. years . 7.7. Adult LongevityLongevity Using means of all possiblepossible estimates (six means;means; three for each tree group) ofjuvenile We hahave,ve, as yet, yet, no adequate means for survivorshipsurvivorship (0.29)(0.29) and adult fecundity (6.2(6.2 directlydirectly estimating adult longevitylongevity from the offspring per year) for all all trees,trees, we obtain a mark-recapturemark-recapture data,data. However,However, if we assume prediction of 1212years of reproductive lifelifeto that the popupopulationslations weobserved observed are stable,stable, successfulsuccessful replacement and a total life-spanlife-span of we can can calculate how long the average aduadultlt 19 yearsyears.. Thisfigure will increase or decrease must lliveiveto replace itselfin the population.population . InIn bbyy about 2 years for the earliest and latestlatest the X trees, trees, juvenilejuvenile survivorshipsurvivorship for 4 years reproducers.reproducers. The number ofextrapolationsextrapolations of (i(i.e.,.e., to achieve about 17 mm length) isis 2.12.1% raw field data necessary to achieve these fig­ (i.e.,(i.e., annualannual survivorshipsurvivorship of 0.33,0.33, the mean uresuresis great,great, andand the resultant predictions ofthe Jolly and Manly-ParrManly- Parr estimates, to the the cannot be considered highlyhighly accurate. How­How­ 3.5th3.5th power). TThehe inverse of0.021, 47.6, 47.6, is the the ever, they do indicate that adultad ult survivorship number of offspringoffspring that must be produced musmustt be closeto that predicted by the various for 1 to survive through through thethe fourth year and methods (i.e.,(i.e., in the high 90's) for these small small reach 17mm. mm . TThishis snail must thenlive more more populationspopulations to persist. thanthan 3 years to achieve reproductive maturity (i.e.,(i.e., the average size at lip formation,formation, 21.321.3 DISCUSSION mm).mm). At 5.2 offspring per year,year, it will then havehave to reproducereproduce for 9 years (i.e., (i.e., 47.647.6 -7--i- 5.2)5.2) The populations of PartulinaPartulina proxima to replace replace itself.itself. Life-span after achieving 17 studied between 11983983 and 1986 are small, small, mm should thus be12 years, years , and totaltotallife­ life­ but,but, basedon other observations we have span shouldshould be over 1616years! made in the woodlandswoodlands ofupper Molokai,Molokai, are For the S treetree,, using the Manly-ParrManly- Parr and typical for this species. species. Survey observationsobservations Jolly estimates for annual survivorship up to of the species have have includedincluded sightings in five ageage4 of0.190.19 anandd a calculated adult fecunfecunditydity different locations across a linear distance of 7.1,7.1, reproductivereproductivelife-span life-span should be 47 greater than 3 km, km, and nowhere have we seen years, a figure difficult to believe. A juvenjuvenileile snails sscatteredcattered evenly across the fufullll ssizeize DemographicDemographic Studies of Partulinaproxima-HADFIELDPartulina proxima-HADFIELD AND MILLER 13

TABLE 4

LIFELIFE HISTORIES OF THREETHREE ACHATINELLINEACHATINELLlNE SNASNAILSILS

Achatinella Partulina Partulina CHARACTER mustelina*muste/ina* redfieredfieldii*ldii* proxima

BirthBirthsize (length,(length, rnrn)mm) 4.5 5.1 4.2 Mean maximum size (rnrn) (mm) 18.4 2323.0.0 21.3 Range (rnrn)(mm) 16.7-20.4 2121-24-24 1919.7-24.4.7-24.4 Age at first reproductionreproduction (yr) 7 4 7 Fecundity (annual) 1I 11-4-4 6 Longevity (yr)(yr) II II 19

•• Data fromfrom Hadfield(1986). (1986).

range,range, norin in great abundance.abundance. Thus,Thus, our We have no adequate explanation for the observations,observations, while deficient in many aspects high mortality rates observed in juvenile (e.g.,(e.g., number ofsnails seen, number ofrecap­ Partulina proxima,proxima, and we lack evidence for tures,tures, growth rate measurements in midsize why these juveniles should be more vulnerable animals), are not likely to be improvedimproved upon,upon , than those of the other species studiedstudied.. A and are at least representativerepresentative of the current number of possibilities existexist,, including the status ofthe species. species.Past population sizessizesandand following: (1) Theymay suffer more quickly densities of P.P.proxima are impossible to esti­ from desiccation and may lack behavioral mate from recent data, and nowhere in the traits that keep them in moist, shaded parts of literatureliterature have we found reference to the bi­ the trees during periods ofintense solar expoexpo­­ ology or abundance of this species. species. sure.sure. (2) They may be more readily dislodged The low densities of adults of Partulina by winds and become "lost" in the grassy proxima are not typical of most other acha­ areas surrounding the study trees, where they tinelline species wehave studied (Hadfield may fall prey torats, the predatory gastropod 1986,1986,Hadfield and Mountain 1980). How­ OxychilusOxychilus sp.sp.,, and perhaps other unrecognized ever, we have unpublished observations of predators. (3) They may be less efficient in Achatinella sowerbyana on Oahu that suggest finding sufficientfood among the scattered aasimilar fragility fragility of populations.populations. For popu­popu­ patches of fungus on the leaves of the o'hia lationslations of P.P. redfieldii on Molokai and A. trees. (4) Or, theymay suffer from an uniden­ mustelina on Oahu, preliminary data showed tified pathogen, perhaps an introduced virus a much much greater density of adults, greater num­ or bacterium.bacterium. Captive studies, only recently bers of snails in midsize classes, and higher begun, may shed light on these possibilities. juvenilejuvenile survivorship (Hadfield 1986). Partu­ Migration does occur in Partulina proxima, linalinaproxima isis unique among thesethesespecies in as demonstrated by occasional and brief ap­ itsits higherjuvenile juvenile mortality, longer estimated pearance in our study trees oflargeoflarge snails that life-span,life-span, and higher fecundity (see Table 4). 4). we have labeled ""transients."transients." On one occa­ AtAt6 offspring per year per adult,adult, this species is sion, we moved twolarge snails from one tree at least least 2-62-6 timestimes morefecund than other to another,another, only to find them eventually back speciesspeciesfor which we have estimates (Hadfield in the tree from whichthey were removed. 1986,1986,Hadfield and Mountain 1980). Low Follow-up studies on the homing abilities of numbersnumbers ofadults can colonize new trees suc­ P. proxima have not been donedone.. However, cessfullycessfullyonly if they retain a fecundity of this while large snailsare known to be able to magnitude for more than 1212years!years! PopulationPopulation move from tree to tree, small snails appear to stability,stability,if indeed that is the current status, is stand less chance of such migrationmigration.. We have accomplished by two major facets of the life attempted to detect such activity by carefully history of thisthis species: great adult longevity examining bushes andtrees near the study and relatively high fecundity. fecundity . trees for thepresence of labeled juvenilesjuveniles.. 14 PACIFIC SCIENCESCIENCE,, Volume 4343,, JanuJanuaryary 19891989

None have been foundfound.. Additionally, if the Neither the camaenids of Puerto Rico nor L. "mortality""mortality"of youngyoung snailssnails was to be ex­ fasciatus from Florida appear to bein im­ plainedplained by out-migration,out-migration, one would expect mediate danger of extinction (Heat(Heatwolewole and that,that, due to chance alone,alone , equal numbers of Heatwole 1978,1978, Voss 1976). small ssnailsnails would in-migrate.in-migrate. Among ververyy The Partulidae oftropical islands stretching small snailssnails,, this could be occurring and re­ across the Pacific from the Marianas in the main undetected. HoweverHowever,, migration cannot westwest to the Society Islands in the east were explain the virtual aabsencebsence ofsnails in midsize monographed byby Crampton (1916,(1916, 1925,1925, classes(10-16 (10-16 mm);mm); they appear to be no 1932),1932), and some Moorean partulid species more abundant in trees near the study trees have become models for laboratorylaboratory study of than in the S and X trees themselves. The patterns of inheritance in gastropods (e.g.,(e.g., intense loyalty we have observed of most Murray and Clarke 1966).1966). Members of the snails to single trees is in agreement with Partulidae resemble the achatinelline snails in earlier natural history observations on other many aspects, aspects, including habitat (some even Partulina species(e.g., (e.g., H.W. Henshaw in live on the same genera of trees), viviparity, viviparity, Pilsbry and Cooke 19121912-1914).-1914). and, at least in some species, food habits Other families include threthreatenedatened tree snails, snails, (Crampton 1916, 1932). 1932).However,However, the partulas but for none of them do wehave data com­ are distinctly different in their much higher parable to those presented here and earlier for growth rates,rates , earlier ages at first reproduction the Hawaiian achatinellines (Hadfield 1986, 1986, (10 months-1.5 yearsyears),), andhigher annual Hadfield and Mountain 1980). In the higher­ fecundities (16-19 (16-19 offspring per year) (Murray elevationelevation forests of Oahu and Molokai,Molokai, Ha­ and Clarke 1966). LifeLife-spans-spans of the Partula waii,waii, many other arboreal gastropods co-exist species hahaveve notbeen determined. with the achatinellineachatinellines,s, including species of We cannow return to the major question AuriAuriculella,culella, Tornatellides,Tornatellides, Philonesia,Philonesia, and posed at the beginning of thispaper: What Succinea.Succinea. In many areas,areas, species in some makes the achatinelline snails particularly of these genera persist whwhereere achatinellines vvulnerableulnerableto the agents of extinction (habitat long ago disappeared. Comparisons of these destruction,destruction, predators,predators, collectors)?collectors)? It appears hardier survivors with the achatinellines that great loss of juvenile snails istypical of would be useful. They may show great dif­ the species species studied here,here, and predation may be ferences in reproductivereproductive mode (several are a partial causecause.. In light ofthis high early mor­ oviparousoviparous and more fecund), growth rate,rate, and tality,tality, populations survive only by the rela­ age at maturation. tively high fecundity (compared to other Other well-studied tree snails show interest­ achatinellines) and great longevity of adults. ing contrasts with achatinellines like Partulina It is clear that any agent that selectively de­ proxima.proxima. What weknow of the life histories of stroys the adults (such as visual predators ththatat groups such as the Liguus species of Florida do not detect the more numerous juveniles) and the Caribbean (Davidson 1965,1965, Tuskes would quickly annihilate the populations.populations. If a 1981,Voss1981 , Voss 1976) 1976)andand the camaenids ofPuerto populationpopulation ofadults isonly 4 snails (such as in Rico (Heatwole and Heatwole 1978) shows treeS), and they are producing,producing, altogether, them to be oviparous animals with annual­ only 28 28juvenilesjuveniles a year, year, then at a survivorship not continuous-reproduction. Both Liguus rate of 0.29 (theaverage for all trees by all and the camaenids lay their eggs inthe ground methods) at least 3 yearsof offspring produc­ in relatively large clutchesclutches.. However,However, these tion are required for a single adult ""replace­replace­ snails resemble the achatinellines in maturing menment."t." Ifa rat or a human collector took all 4 late [about 4 yearsfor L. fafasciatussciatus (Tuske(Tuskess adults from such a tree on one occasionoccasion,, the 1981,1981 , Voss 1976)1976),3-6,3-6 years for the camaenids population would essentially be dead. We (Heatwole and Heatwole 1978)]. Liguus fafas­s­ have foundpiles ofeexclusivelyxclusivelylarge, large, rat-killed cciatusiatus may live6live 6 yearyearss or longer (Tuskes (Tuskes 1981)1981),, sshell~hells aamongmong nearbynearby,, dense populations ofthe and some of the Puerto Rican camaenids live congener Partulina redfieldii. redfieldii. Furthermore,Furthermore, up to10 10yearsyears (Heatwole and Heatwole 1978).1978). well-documented collections in museums museums could

41N6 Demographic Studies of Partulina proxima-HADFIELDproxima-HADFIELD AND MILLERMILLER 15 easily represent the type ofharvesting by col­ air faresfor our early trips and a field vehicle lectors that would be destructive (see also for access to the study sitesite.. To Alan Holt Hadfield 1986).1986). and Ed Misaki of The Nature Conservancy As previously noted (Hadfield and Moun­ go our greatest thanks. Twenty-three people­ tain 1980), 1980), the achatinelline snails appear to students, faculty and professional colleagues, have evolved in the absence of predators. We and members of our families:-assistedfamilies-e-assisted in the may thus assume that these snails, like other field work at various times.times. To all ofthem we fragile island species,species, owe their imminent ex­ express our deepest appreciation, and espe­ tinction to their lack of protective structures cially to Barbara A. Shank,Shank, a very steady par­ or behaviors,behaviors, their currently maladaptive life ticipant in the first half of the field studies; history characteristics, and the abundant and Marilyn Switzer-Dunlap,Switzer-Dunlap, who often willingly varied destructive agents now existing over filled a suddenly empty slot at the last mo­ their greatly restricted habitat ranges.ranges. Preser­Preser­ ment; and Anne Harrington Carwile,Carwile, Bruce vation of remaining habitats, eradication of Koebele, Leslie Ho, and Gareth Mendonsa, introduced predators, and, most importantly, for helping on numeroUsnumerous trips.trips. Peter C. a more exact understanding of the causes of Galloway and E. Jane Albert, aswell as juvenile mortality are central issues in the providing field assistance on a number of preservation of species such as Partulina occasions, provided the photographs for Fig­ proxima.proxima. The Moorean Partula species van­ ures 1 and 2, respectivelyrespectively,, for whichwe are ished at a great rate,rate, and this was due to at extremely grateful. Small grants from the least one ofthe same factors that is destroying Hawaiian Evolutionary Biology Program and the Achatinella species of Oahu-theOahu-the intro­intro­ the University of Hawaii Research Council duced predatory gastropod Euglandina rosea have helped to support these studies. (Clarke et al.a!. 1984, Murray et a!. al.1988). The achatinellines have been vanishing for a long period of time, longer than the occupancy of LITERATURE CITED the Hawaiian Islands by E. rosea. rosea. However, this latter-day predator may be destined to ANONYMOUS. 1985.1985. IUCN points to plight of destroy the high-elevation, isolated popula­ the world's threatened plants and animals,animals, tions that survived long-term habitat destruc­ parks and reserves. Oryx 12: 69-69-71.71. tion and the collectors. The destruction ofthe BEGON, M.M. 1979.1979. Investigating animal abun­ Moorean Partula species shows that even early dance: Capture-recaptureCapture-recapture for biologists. reproduction and a 200-300%200-300% greater fecun­ University Park Press,Press, Baltimore. dity were not sufficient to offset the depreda­ BERGER, A. J.J. 1970.1970. The present status of the tions ofa predator like E.E. rosea.rosea. Introduction birds ofHawaii.Hawaii. Pac. Sci. 2424::29-42. ofnonnative plants and animals (often for the CARLQUIST, S.1970. 1970. Hawaii: A natural his­ best ofhumanitarian reasons) for which there torytory.. Natural History Press, Garden City, are no adequate means of regulating popula­ N.Y.N.Y. tion growth,growth, is the critical factor that has CLARKE, B.,B., JJ.. MURRAY, and M. S. JOHNSON. sealed the fate of the Moorean partulas and 1984.1984. The extinction ofendemic species by a possibly the Hawaiian achatinelline snails as program ofbiological control. Pac. SciSci.. 38: well. 97-104. COOKE,COOKE, C. M.,M., JR., and Y. KONDO.KONDO. 1960.1960. Re­ vision ofTornatellinidae and Achatinellidae (Gastropoda, Pulmonata).Pulmonata). Bull. B. P.P. Bishop ACKNOWLEDGMENTS Mus. 221: 1-303. 1-303. These studies could not have taken place CRAMPTON, H.H . E. 1916. 1916. Studies on the varia­ without the solid and enthusiastic support of tion, distribution, and evolution ofthe genus The Nature Conservancy of Hawaii.Hawaii. The Partula: The species inhabiting Tahiti.Tahiti. work was carried out on their Kamakou Pre­ Carnegie Inst. Washington Pub!.PubI. 228:1­ 1­ serve on Molokai, Hawaii, and they provided 313. 16 PACIFIC SCIENCESCIENCE,, Volume 43, JanuaryJanuary 1989

---.- -- . 1925.1925. Studies on the variation,variation, distri­ Ecology of the PuertoPuerto Rican camaenid bution,bution, and evolution ofthe genus Partula:Partula: treesnails. snails . MalacologiaMalacologia 17:241-315.17:241-315. The species of the Mariana Islands,Islands, Guam KONDO, Y.Y. 1970.1970.Colloquium Colloquium on endangered and SaipanSaipan.. Carnegie Inst.lnst. Washington species of Hawaii;Hawaii; extinct land molluscan Publ.PubI. 228A: 1-116.1-1 16. species.species. Rept.,Rept., meeting at U.S. National -----.1932.-. 1932. StStudiesud ies on the variationvariation,, distri­ Museum.Museum. bbution,ution, and evolution ofthe genus Partula:Partula: MURRAY,MURRAY, J., and B. CLARKE.CLARKE.1966. 1966. The inheri­ The species inhabiting Moorea. Carnegie tance of polymorphic shellshell characters in Inst.lnst. Washington Publ. 410: 1-335. 1-335. Partula (Gastropoda).(Gastropoda).GGeneticsenetics 5454:: 1261­1261­ DAVIDSON,DAVIDSON, TT.. 1965. Tree snails,snails, gems of thethe 12771277.. Everglades.Everglades . Nat. Geographic 127:127 :372­ MURRAY, J.,J., E. MURRAY,MURRAY, M.M . SS.. JOHNSON,JOHNSON, and 387.387. B. CLARKE.CLARKE.1988. 1988. TheThe extinction of Partula FOSBERG, F.F . R., and D.D . HERBST. 1975.1975. Rare on MooreaMoorea.. Pac.Pac . Sci.Sci. 42(3-4):42(3- 4): (in press). press) . and endangered species ofHawaiian vascu­vascu­ NEAL, M. C. 1928. AnatomicaAnatomicall studies of lar plantsplants.. AAllertoniallertonia 1: 1-72. 1-72. Achatinellidae.Achatinellidae. Bull.Bull. B. P.P. Bishop MuMus.s. 47: GAGNE, W.W. 1982.1982. Working toward anassess­ assess­ 34-49.34-49. ment ofthe conservation status ofHawaii's PILSBRY,PILSBRY, H.H. A.A.,, and C. M. M . COOKE,COOKE, JJR.R. 1912­1912­ endemic arthropodsarthropods with emphasis on 19141914.. Manual ofconchology,conchology, structural and moths (Lepidoptera). Pages 6363-72-72 in Proc. systematicsystematic.. SerSer.. 22,, Vol. 2222.. Achatinellidae. 4th Conf. Nat. Sci. Hawaii.Hawaii. Academy ofNatural Sciences,Sciences, Philadelphia.Philadelphia. GAGNE,GAGNE, W.,W., and F.F . HOWARTH.HOWARTH. 1982.1982. Con­Con­ SEVERNS,SEVERNS, R.R.M. 1981. 1981. Growth rate determina­ servationservation status of Hawaiian LepidopteraLepidoptera.. tions of AchatinellaAchatinella lila,lila, a Hawaiian tree Pages 74-84 74-84 in Proc.Proc.3rd Congr. European snail. Nautilus 95:95 : 140-144.140-144. Lepidopterol.Lepidopterol.,, Cambridge. SOKAL,SOKAL, R.R. R.,R., and F. J. RROHLF.OHLF. 1981.1981. Bio­Bio­ GGULICK,ULICK, J. TT.. 1905.1905. Evolution, raciaraciall and metry,metry, the principlesprinciples and practice of sta­ habitudinal. Carnegie Inst.lnst. Washington tisticsin biologbiologicalical researchresearch.. 2nded. WW.. H.H. Publ. 25:i25 :i-xii,-xii, 11-269.- 269. Freeman,Freeman, San Francisco.Francisco. HADFIELD,HADFIELD, MM.. G. 1986.1986. Extinction in Hawai­ TusKEs,TUSKES, P.P. M. 1981. PopulationPopulation structure and ian achatinelline snails. Malacologia 27: biology ofLiguus tree snails on Lignumvitae 6767-81.-81. Key, Florida.Florida. NautilusNautilus 95:95 :162-169. 162- 169. HADFIELD, M.M . G.,G., and B. SS.. MOUNTAIN. 1980.1980. Voss, R. R. SS.. 1976.1976. Observations on the ecology Afield study of a vanishing species, Acha­ of the Florida treesnail, snail, Liguus fasciatusfasciatus tintinellaella mustelina (Gastropoda, Pulmonata), (Muller).(Muller). NautilusNautilus 90: 65-69. 65-69. in the Waianae Mountains of OahuOahu..PPac.ac. ZIMMERMAN,ZIMMERMAN, E. C. 1970.1970.Adaptive Adaptive radiation SciSci.. 3434::345345-358.-358. in Hawaii with special special reference to insectsinsects.. HEATWOLE, H., and A.A. HEATWOLE.HEATWOLE. 1978. Biotropica 22::3232-38.-38.

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