Diversityand Distributionof Communities in Puerto Rico1

Juan A. Torres Departamentode Biologia, Colegio UniversitarioTecnol6gico de Bayam6n, Bayam6n, Puerto Rico 00620, U.S.A.

ABSTRACT I studiedants in upland tropicalforest, grassland and agriculturalland in San Lorenzo,Puerto Rico, to uncoverfactors responsible forthe distributionand numberof speciesin thesecommunities. Observations, laboratory studies and fieldexperiments were used. Microclimateinfluenced the distributionsof Pheidolefallax, Solenopsisgeminata and Monomoriumebeninum; forest had lower toleranceto high temperaturesthan ants fromnon-forested areas. In addition, ants did not toleratehigh temperatures as well as ants in the Formicinae, and .The largernumber of speciesin non-forestedareas is correlated withlarger food overlaps,tighter guilds, a more variablemicroclimate, and higherlevels of aggressiveness.

RESUMEN Estudielas hormigasen areasadyacentes de bosque tropical,pradera y zonas agricolasen San Lorenzo,Puerto Rico. Observaciones, estudios en el laboratorioy experimentosde campo fueronrealizados para tratarde descubrirlos factoresresponsables de la distribuci6ny el numerode especiesen estas comunidades.Encontre que las distribucionesde Pheidolefallax, Solenopsisgeminata y Monomoriumebeninum son altamenteinfluenciadas por el microclima.Las hormigasdel bosque toleranaltas temperaturasmenos que las hormigasde areasno forestales.Ademas, las hormigasde la subfamiliaPonerinae toleran altas temperaturasmenos que las que pertenecena las subfamiliasFormicinae, Myrmicinae y Dolichoderinae.El numeromayor de especiesde hormigasen areas no forestalesesta relacionadoal mayorsolapamiento alimenticio, gremios mas compactos,un microclimamas variabley nivelesmas altos de agresividad.

Two PROBLEMS THAT ECOLOGISTS ADDRESS are the identifi- overlap,and microclimatediversity to determinethe con- cationof thosefactors that determine the distribution and tributionof thesefactors to thenumber of speciesin three numberof speciesin a community. distributions adjacent ant communities.Also, ant toleranceto high have been found to be affectedby climate,nutritional temperatureis analyzedto assess its contributionto ant requirements,predators, competitors and dispersalbar- speciesnumbers. A companionpaper discusses the subject riers(Andrewartha and Birch1954, Krebs 1972). Several of ant coexistencein thesecommunities (Torres 1984). factorshave been found to accountfor differences in species numbers.Paine (1966) and Harper (1969) found that predationon superiorcompetitors increases diversity by HABITATS AND ANTS keeping the weak competitoron the system.Connell (1978) suggestedthat disturbancesintermediate in fre- FromJuly 1978 to September1980, I studiedants in a quencyand intensityshould accountfor high diversity in subtropicalwet forest,grassland dominated by Chloris coral reefsand tropicalrain foresttrees. Increase in area radiata and agriculturalcrops in San Lorenzo, Puerto resultsin higherdiversity due to its effectin reducing Rico. Cropsconsisted of coffee(Coffea arabica), plantains extinctionrates (MacArthur and Wilson 1967). Greater (Musa paradisiaca), and yams (Dioscorea alata). These resourcediversity, smaller niche breadth,greater mean habitatswere located near Route 7740 (forest:Km 4.4; nicheoverlap, compact guilds, through their influence on grasslandand crops:Km 1.1-2.5). The tightforest can- speciespacking (Inger and Colwell 1977) and stochastic opy produceda microclimatecooler and wetterthan in phenomena(Sale 1977, 1982; Caswell 1978) have been thegrassland and plantain-yamscrops. Coffee groves and foundto be relatedto diversitypatterns. foresthad similarmicroclimates. The forestcontained 20 Througha seriesof experimentalfield studies, I tried ant species,the grassland37, and agriculturalland 38 to determinethe influenceof food competitionand mi- (see accompanyingpaper for a listof species).Thirty-four crodimateon the distributionof Pheidolefallax, Mono- species were shared by grasslandand agriculturalland, moriumebeninum and Solenopsisgeminata. In addition,I and ten were foundin all threehabitats. The same ants conductedanalyses of food diversity,food breadthand tendedto be foundin coffeegroves and forest.Excluding the coffee-grovesspecies, agricultural land species were I Received 3 February1983, final revision9 January1984, similarto thosefound in grassland.Iridomyrmex melleus accepted 16 February1984. and Myrmelachistaramulorum were found once on grass-

296 BIOTROPICA 16(4): 296-303 1984

This content downloaded from 166.4.81.212 on Thu, 25 Feb 2016 16:07:15 UTC All use subject to JSTOR Terms and Conditions land and mighthave been transientmembers of thiscom- I transferredfive additional nests from grassland to grass- munitysince they were usually found in shaded areas. land approximately250 m fromthe forestto controlfor Due to the insulareffect, the faunain thesehabitats movingeffects. Observations were made as in Monomo- is depauperate,and ants are an example.Ants foundon riumebeninum's experiments. The experimentended on the island are generallysmall. Representativesof larger April27, 1980 whenthe fruitswere opened to checkfor Camponotiof the maculatusand abdominalisgroups are live ants. The experimentwas repeatedfrom April 3 to absent(Wheeler 1908). Neotropicalgenera such as Atta, April27, 1980. The reasoningbehind these experiments Azteca and Eciton are also absent and Crematogaster,was the same as forthe M. ebeninumexperiments. Pseudomyrmexand Pheidole,well developed in tropical The ground-nestingPheidole fallax was almost im- mainland,are scarcein PuertoRico (Wheeler 1908). possibleto transplant.I constructeda shade in situ over P. fallax nestssimulating the forestcanopy. The shade produceda coolerand wettermicroclimate compared to controlunshaded nests. I drovefour wooden stakesat a METHODS distanceof 18 cm fromnest openings and fixeda 28 x FIELD EXPERIMENTS.-Monomortiumebeninum, Solenopsis 50 cm wire net coveredwith cloth to the stakes. Rain geminataand Pheidolefallax are grasslandand agricul- waterpercolation was normalthrough the shade and light turalland ants found in forestgrass-covered dirt roads intensitywas approximately50 percentof unshadedareas but not withinthe forest.I conductedexperiments to and approximately25 percenthigher than in the forest. determinethe factorsthat barredthese species from the Controlshad fourwooden stakesdriven at the same dis- forest. tancefrom the nestwith dothless wire nets. The experi- On July3, 1980 I introducedto the forestnine logs mentswere performed three times involving four nests as containingMonomortium ebeninum colonies to whichI fed experimentalunits and fouras controls,and were con- honeyand tuna fishevery other day. Six othernests were ductedin 1980 on 9 Feb-22 March, 19 Feb-27 April, introducedbut not fed.I transferredsix nestsfrom grass- and 5 July-26 Sept. Observationswere made weekly. land to anothergrassland 200 m fromthe forest as control formoving effects. I fed tuna fishand honeyto six ad- TOLERANCE TO 45?C.-Surface temperaturesof 450C and ditionalnests in the grasslandto determinetheir nutri- higherwere experienced by antsthat foraged during mid- tionaladequacy as ant food. I isolatedall fed nestsfrom day, and few ant speciesforaged in these temperatures. interspecificinterference by hangingthese fromtrees or Since 45?C representsa realistic,but potentiallylimiting fenceposts and applyingautomotive grease to thestrings. temperature,I studied ant toleranceto 45?C in an envi- Grease was applied to unfednests but in a mannerthat ronmentalchamber (Environator Model WL221). The allowed antsto leave and re-enter.I observednests every chamber'scover was replacedwith glass to enable obser- threedays and placed food nearunfed nests to checkfor vationof ants. I placed a minimumof ten ants at 45?C ant presenceand removedit when activitywas observed. in vials withperforated caps to allow air circulation.The The experimentended on September25, 1980 whenlogs timeit took 50 percentof the antsto assumea crouched weresplit open to searchfor ants. Presenceor absenceof positionwas taken as a measureof toleranceto 450C. I ant coloniesand theirconditions were recorded. If micro- replicatedeach experimentwith individuals from ten col- dimate is the factorbarring these species from the forest, onies formost species. fedand unfednests in the forestwould disappear;on the otherhand, if competitionfor food is the limitingfactor FIELD TEMPERATURES AND NICHE METRICS.-I measured fed nestsshould remainand prosperwhile unfed nests ground and vegetationtemperatures under shade and should die, disappearor not prosper. sunlightat randomlychosen times of day for the three Finally,four M. ebeninumnests were introducedto habitatsusing YSI telethermometersand with the help the forestand fed but not isolatedto studyinterspecific of two assistants.Information on food habits was ob- interactions.I brought three Solenopsis B (mainlya forest tainedby observingant nestsfor five minutes each hour. species) neststo the grasslandon a sunnyday and put Food that ants were carryingwas removedwith forceps themnext to threeM. ebeninumnests. Food was placed or a piece of adhesive tape and later identifiedin the betweenthe neststo studyinterspecific aggression. laboratory.In addition,gastric distention, which occurred On March 23, 1980 I introducedto the forestten when liquid food was brought,was recorded.To study coconutfruits containing Solenopsis geminata nests. Five microhabitatutilization, I put baits simultaneouslyon werefed with Chlorisradiata seeds,tuna fishand honey ground,rock, litter and vegetation(at randomlychosen everyother day. S. geminatanests were not isolatedfrom times) at a distanceof 5-15 m fromeach other.This antinterference due to thisspecies' aggressiveness. S. gem- was done in sunny,shady, wet and dryareas, during night inata is able to defeatthe majorityof PuertoRican ant and day. Speciesfound on the bait and insidea 25 cm2 speciesunder all environmentalconditions (Torres 1981). quadrat put aroundthe bait were recorded.In addition, Diversityand Distributionin Ant Communities 297

This content downloaded from 166.4.81.212 on Thu, 25 Feb 2016 16:07:15 UTC All use subject to JSTOR Terms and Conditions TABLE 1. Fates ofMonomorium ebeninum nests subjected to TABLE 3. Fates of Pheidole fallaxnests subjected to different differentexperimental treatments. experimentaltreatments.

Forest Grassland Shaded Unshaded Total Fed Unfed Unfed Fed Total Remained 1 8 9 Moved 1 1 4 15 Remained 6 1 4 4 15 Died or disappeared 3 5 2 2 12 Total 12 12 24 Total 9 6 6 6 27

nopsisB and withindays the lattermoved its nestsinto I recordedinterspecific aggressive interactions at baits. I the logs previouslyoccupied by M. ebeninum.Solenopsis calculatednoncircular niche metricsusing the Colwell- B killed most M. ebeninumthat surfaced to feed. These Futuyma(1971) measureswith absoluteweighting fac- specieswere similarin size and had complementarydis- tors. tributions:M. ebeninumwas foundin sunnyareas whereas SolenopsisB was foundin shaded ones. The threeSole- nopsisB nestsbrought from the forestand put nearnests RESULTS of M. ebeninumin sunnygrassland were easilydefeated FIELDEXPERIMENTS.-Fisher's exact test (one-tailed)was by thelatter at tuna fishbaits. This alternatingsuperiority used to analyzefrequencies of fatesof nests(Tables 1- was relatedto differencesin tolerancesto temperature(see 3). Fed nestsof Monomoriumebeninum did not survive Torres1984), and indicatesan effectof microclimateon betterthan unfed ones in the forest(Table 1, P = 0.08) thedistribution of thesespecies. Thus, aggressionby Sole- suggestingthat lack of food did not bar the speciesfrom nopsisB and M. ebeninum'ssensitivity to low tempera- the forest.There was no differencein survivalbetween turesprevented the latterfrom entering the forest. fednests in theforest and relocatedfed nests in thegrass- All Solenopsisgeminata nests (fed or unfed) disap- land (P = 0.71), nor betweenunfed nests in the forest peared fromthe forestwithin two to threeweeks (Table and relocatedunfed nests in the grassland(P = 0.12). 2). Grassland,unfed, control ants remained in theirnests Fed and unfedgrassland nests did not differin survivor- in contrastto the unfed, forest-introducedants (P < ship (P = 0.73), indicatingthat food offeredwas nutri- 0.001), rulingout the possibilitythat forest results were tionallyadequate. AlthoughI did not finddifferences in caused by movingeffects. Grassland, unfed, control ants nestsurvivorship, M. ebeninum'sactivity was differentin remainedlonger in theirnests than thosein fed nestsin the forest.This specieswas activein grasslandnests and the forest(P < 0.001). These resultssuggest that food inactivein the forestmost of the time. M. ebeninumwas limitationwas not responsiblefor the distributionof S. diurnalin agriculturalland and grassland;on cloudydays geminataand thatmicroclimate was, mostlikely, the de- its activitywas reduced. Only duringunusually warm cisive factor.In the Pheidolefallax experiments(Table days was thisspecies active in the forest.On thesedays 3), antsin shade movedtheir nests 60 to 90 cm to sunny smallerdrops in nighttemperature occurred and M. eben- areas withina week,while control nests usually were not inumcontinued foraging during the night.This suggests moved (P= 0.004), suggestingthat microclimatepre- that warm temperatures,which were rarelyexperienced ventedthis species from entering the forest. in the forest,were needed forforaging in thisspecies. The fourfed nestsof Monomoriumebeninum in the FOOD (DIVERSITY, BREADTH AND OVERLAP).-This study forest(not isolatedwith grease) were attackedby Sole- followedthe analysesdone by Ingerand Colwell (1977) in theirstudy of amphibianand reptileassociations in Thailand.They proposed that to evaluatethe contribution of food diversityto species-numberdetermination, the resourcematrices should be reducedto theresources com- TABLE 2. Fates ofSolenopsis geminata nests subjected to dif- mon to thethree habitats. If, afterdoing so, similarnum- ferentexperimental treatments. ber of species are left in each of the reduced resource matricesthen differences in speciesdiversity are the result Forest Grassland of the extra resources.After reducing the matrices(see Fed Unfed Unfed Total Torres 1981) to the 15 food resourcescommon to the threehabitats, the numberof ant specieswas the same Remained 0 0 7 7 Died or disappeared 10 10 3 23 in the reducedand in the nonreducedmatrices. This in- Total 10 10 10 30 dicatesthat differencesin ant species diversitywere not the resultof the extrafood resources. 298 Torres

This content downloaded from 166.4.81.212 on Thu, 25 Feb 2016 16:07:15 UTC All use subject to JSTOR Terms and Conditions peaks show thatguilds were of approximatelythe same TABLE 4. Food nichebreadths computedfor 15 resourcesin all threehabitats. size in the agriculturalland and grasslandcommunities. Similarityin communityorganization in grasslandand Agri- agriculturalland as comparedto forestis also indicated cultural Grass- by the distributionof mean food overlap(Fig. 1). Species land land Forest Brachymyrmexheeri . 1374b MICROHABITAT(DIVERSITY AND OVERLAP).-Temperatures Brachymyrmexminutus .0963 on the groundand vegetationare summarizedfor days Camponotusustus .0914 and nightsin Figure2. Analysesconcentrate on forestand Cardiocondylaemeryi .1288a .1509 Cardiocondylanuda .0860 .2059 agriculturalland data (grasslandand agriculturalland Cyphomyrmexrimosus .0464 .1502 data were similar).Mean temperaturewas lower in the Iridomyrmexmelleus .1060 .1035 forestthan in non-forestedareas (t-test,correction for un- Monomoriumebeninum .2079 .1340 equal variances,t = 18.91; df = 1022, 400; P < 0.05). Monomoriumfloricola .1240 .1190 Mycocepurussmithi .0889 .0262 I made conservativetests of equalityof variancesselecting Myrmelachistaramulorum .0648c the 0.01 significancelevel. Total variances(Fig. 2) in the Odontomachusbrunneus .1436 .0715 threehabitats were heterogeneous (F,ma = 2.17; df = 3, Paratrechinalongicornis .1328 .1281 400; P < 0.01) pointingto morevariance in temperature Paratrechinasteinheili .1735 .1746 .0609 in non-forestedareas. Temperaturewas morevariable in Platythyreapunctata .0681 Pheidoleexigua .1733 .1875 sunnyagricultural land groundthan in sunnyforest ground Pheidolefallax .0777 .1196 (F= 2.56; df= 53, 48; P < 0.01), while shaded agri- Pheidolemoerens .0335 culturalland and shaded forestground did not differin Pheidolesubarmata .2113 .1537 temperaturevariance (F= 1.56; df= 52, 51; P > 0.05). SolenopsisA .1357 SolenopsisB .0709 Temperaturevariability in sunnyforest ground was no Solenopsisgeminata .1641 .0483 differentfrom that of shaded forestground (F = 1.55; Strumigenyslouisianae .0530 .1114 df = 48, 51; P > 0.05). Statisticalanalyses for vegeta- Tetramoriumbicarinatum .1978 .1814 tion microhabitatsgave similarresults (see Torres 1981 Wasmanniaauropunctata .2271 .1682 fordetails). a,b,c median niche breadthfor agricultural land, grasslandand forestspecies, respectively. TOLERANCETO 45?C.-Species' toleranceto 45?C is pre- sentedin Torres(1984). I performeda two-wayANOVA withspecies and habitatsas factorson the data of tem- peraturetolerance for the species shared by thethree hab- itats(forest, grassland and agriculturalland). Interaction Niche breadthand overlapwere also computedfor betweenfactors was significantand forthat reason I plot- the 15 resourcesin common. This is the only way in ted the mean value foreach species(Fig. 3). Interaction whichniche metrics can be comparedacross habitats (In- was producedbecause some samplesfrom the agricultural ger and Colwell 1977), assumingthe 15 food resources land belong to species found mostlyin closed canopy wereequally abundantin the threehabitats. Food niche crops,the latterhaving a microclimatesimilar to the for- breadthsdiffered (Kruskal-Wallis, P < 0.05) but niche est. A one-wayANOVA using the mean value foreach breadthtended to be smallerin theforest (Table 4) which speciesshowed that species differedin temperaturetol- does not explainthe higher species numbers in non-forest- eranceacross habitats (F= 4.13; df= 2, 21; P = 0.03). ed areas. The Student-Newman-Keuls(SNK) (a = 0.05) proce- Since not all niche overlapsare of equal biological dure showed that organismsin non-forestedareas toler- importance(Inger and Colwell 1977), it is bestto analyze ated high temperaturesbetter than forestorganisms and overlapswith the notion of nearestneighbor. Figure 1 that therewas no differencein toleranceto temperature showsmean overlapswith the first, second, . . . , ithnear- betweengrassland and agriculturalland organisms. est neighborfor the speciesin the threehabitats. Mean I performeda two-way ANOVA (habitats and food overlapswere higherin the agriculturalland and subfamilies)on toleranceto 450C forall the speciesfor grasslandcommunities at all ordersof nearness.The stan- whichI have data on thesevariables (Table 5). Subfam- dard deviationsof overlaps(Fig. 1) show that commu- iliesin non-forestedareas tolerated high temperatures bet- nitiesconsisted of tighterguilds in thenon-forested areas. ter(SNK, a = 0.05). The subfamilyPonerinae withstood This is indicatedby the peak of the distributions,which high temperaturesless well than the Formicinae,Myr- occurswhen the orderof nearnessbegins to exceed the micinaeand Dolichoderinaesubfamilies (SNK, a = 0.05). averageguild size (becauseat thispoint overlaps are with- These highertemperature tolerances in non-forestedareas in guilds and betweenmembers of differentguilds). The correlatewith the higher temperatures experienced in these Diversityand Distributionin Ant Communities 299

This content downloaded from 166.4.81.212 on Thu, 25 Feb 2016 16:07:15 UTC All use subject to JSTOR Terms and Conditions ,40- .10 /~~~~~~~~~~~~A *=oref st: .36 *=agriculturol land=0 -09 / \ *~~~~~~~~~~=grassland =0

.32- Co

0 C~~~~~~~~~~~~~~~~~~0 .28- 0> .24~~~~~~~~~~~~~~~~~~~~~~~0

28 6 O1 3141 71 92 oOL 04 23 3 I4 5.0~ 0 n b. .24- ~ ~ ~ ~ ~ eons Order 6 o

FIGURE 1. Mean food overlapand standarddeviation of food overlapof firstthrough nth nearestneighbors. Dark symbols indicatemean and open symbolsindicate standard deviation.

areas.Variances in toleranceto 45?C did not differacross Experimentswith Monomorium ebeninum showed that habitatsin the Ponerinae(Fm = 2.07; df = 3, 3; P > temperatureaffected this species in two differentways: by 0.05). The Myrmicinaeexhibited almost no variabilityin reducingcolony activityand by modifyingits fighting the forestbut theydid exhibita huge variabilityin non- abilities.Monomorium ebeninum's sensitivity to relatively forestedareas (Fm,ax= 137.2; df = 3, 5; P < 0.01). low temperatureswill continueto bar it fromthe forest regardlessof the removalof SolenopsisB fromthe forest. DISCUSSION M. ebeninumswitched to nightforaging when nocturnal foresttemperatures were high to tryto compensatefor Field experimentsdemonstrated that microdimate played thosedays in whichtemperatures were not high enough an importantrole in ant speciesdistribution in the com- to allow foraging.Whitford and Ettershank(1975) found munitiesstudied. Microclimateis importantto ants in thatNovomessor cockerelli switch their pattern of foraging termsof theirforaging activities and nestingplaces (Goss- accordingto the temperature,cloudiness or degree of wald 1951, Brian 1956, Brown 1973, Hunt 1973, Lev- groundhumidity. Sanders (1972) suggestedthat shifts to ins et al. 1973, Lieberburget al. 1975, Trempler1976, crepuscularityor nocturnalityin Camponotusspp. were Taylorand Adedoyin1978, SmaUlwoodand Culver1979, temperatureadaptations. In addition,Hunt (1973) was Whitfordet al. 1981). Temperatureis veryimportant in able to produceshifting in activitypatterns by shading the developmentof larvae and pupae in ants (Wilson the nestsof Dorymyrmexantarcticus and Tapinomaant- 1971). Solenopsisgeminata larvae and pupae seem to arcticumin Chile. Nonetheless,Hodgson (1955) did not need high temperaturesfor theirdevelopment because findcompensation through increases in nightactivity in theywere kept at the top of the mound wheremaximal Atta cepha/otes,even when thisspecies loses a greatpart temperatureswere recorded (pers. obs.), and thisis prob- of its day-foragingtime due to rain. ably one reasonfor its absencein the forest. In the case of Pheidolefallax, microclimatealso af-

300 Torres

This content downloaded from 166.4.81.212 on Thu, 25 Feb 2016 16:07:15 UTC All use subject to JSTOR Terms and Conditions 35 33 31 / Agricultural land Grassland t 29- 27- 25 -So/enopsis A

Ul 0~~~~~0 23 - A So/enopsis B a\) 0 FIGURE 2.Tmertrsmaiso ay()a 21- Forested. 19- r) ~ ~ ~ oa F: 7 g i. 8 mlnufus */ , ; > * P 15 ~~~stlgma 15- 0 H- H opoclor 0 13 So/enopsisC

o: 0 Nl 11 AX,._* _._- -._ -* A inoyr, 0 -

9-U 7 - 5. 0 z~~~

Forest Grassland Agricultural land

FIGURE 3. Mean toleranceat 45?C for the species in the threehabitats. Tolerance is indicatedby the time requiredfor 50 percentof exposed ants to assume a crouchedposition.

FIGURE 2. Temperaturesummaries for day (D) and night (N) on vegetationand ground.T = total. Mean (verticalbar), range (horizontalbar) and one standarddeviation (rectangle) are indicated. numberof warm,dry nest sites resulting in a reduction in the numberof ant colonies.Taylor and Adedoyin (1978) foundthat the distribution of antsin Nigerian cocoafarms depended on thedegree of shadiness.Ants fectedthe outcomeof combatswith Pheidolesubarmata areabsent 2300 metersabove sea levelin closed-canopy (see Torres1984). P. fallax won daily combatsin sun- forestseverywhere, especially in thetropics (Brown 1973). lightbut lost nightand shade combats.P. fallax's poor On treelessslopes at higherelevations (3500-4000 m) fightingabilities in shade and duringthe nightcould be antsmay be abundantsuggesting that radiant heat con- a reasonfor its absence from the forest. Tolerance to 45?C trolsdistribution (Brown 1973). Workingwith Chilean was correlatedwith these species' fightingabilities (P. ants,Hunt (1973) foundthat artificially shaded Tapi- subarmatatolerated high temperaturesless well than P. nomaantarcticum move their nests to unshadedlocations. fallax). Wheeler(1910) discussesseveral examples where he found The effectof shade on ants has been documentedin thatants are more abundant in eastern and southern slopes otherant communities.Brian (1956) foundthat increases amongtemperate zone ants.The distributionof Irido- in shade due to the gradualgrowth of treesreduced the myrmexhumilis is alsohighly influenced by dimatic con- ditions(Brown 1973, Trempler1976). Thesestudies, togetherwith my findings,suggest that temperature is one of themost important factors regulating ant distri- TABLE 5. Two-wayANOVA for temperature tolerance to 450C. butionsin all regionsof the world. Factorsare ant subfamiliesand habitats.A loga- The Ponerinaedid notwithstand high temperatures rithmictransformation ofthe data was performedto reduceheterogeneity ofthe variances. well.This couldbe the reasonthis subfamily's species werefound mostly in wet-shadedplaces. In termsof tol- Sourceof eranceto hightemperatures, the Ponerinae were close to variation df MS F P theMyrmicinae in the forest but closer to theFormicinae Habitats 2 .731 8.38 .001 in agriculturalland. This occurred because the Myrmici- Subfamilies 3 .535 6.12 .001 nae thatentered the forest were those that tolerated or Interaction 6 .028 0.32 .924 preferredlow temperatures,whereas in agriculturalland Explained 11 .322 3.69 .001 membersof thissubfamily that tolerated high Error 67 .087 tempera- tureswere found together with low tolerance Total 78 .120 species.The highvariability in temperaturetolerance in theMyrmi-

Diversityand Distributionin Ant Communities 301

This content downloaded from 166.4.81.212 on Thu, 25 Feb 2016 16:07:15 UTC All use subject to JSTOR Terms and Conditions cinae has contributedto theirexploitation of more cli- with smallerareas than the forestwhich, nevertheless, maticallyvariable habitats like thosepresent in non-for- containedmore ant species;this makes unlikelyan area estedareas. effectfor these diversity patterns. These islandswere ho- There are severalfactors associated with the higher mogeneousin vegetation,eliminating the possibilitythat numbersof species in non-forestedareas. First,the oc- greaternumbers of specieswere due to greatermacrohab- currenceof open and closed-canopycrops allowed forthe itatcomplexity. highestnumber of speciesin the agriculturalland (cor- Ox-plowingwas carriedout once or twicea yearin rectingfor transient species found in the grassland).The agriculturalareas disturbingthe ant community,but it presenceof closed-canopycrops permitted several forest recoveredquickly. The factthat grasslandant numbers ant speciesto enterthe agriculturalland. Second,higher weresimilar to thoseof the agricultural land (whenspecies food overlapsand tighterguilds are associatedwith a restrictedto coffeegroves were not taken into account) greaternumber of speciesin non-forestedareas. Micro- points to a minimal effectof plowing in determining habitatdiversity affected the degree of overlapin thefood speciesnumber. Also, thefact that overlaps and thetight- niche dimension.Its effectswere greaterin non-forested ness of guildswere almost identical in the grasslandand areas due to greatervariability in microclimate,as indi- agriculturalland ant communitiesalso supportsthe con- cated by the fieldtemperature data. The presenceof a tentionthat plowing did not affectthe organizationin morevariable environment affects the distributionof re- thesecommunities. Ant recoveryafter disturbance is fa- sourcesthrough its influence on ants'daily activities, patch cilitatedby thefacts that ants do not build elaboratenests utilization(in time) and outcomeof aggressiveinterac- like many othersocial (Wheeler 1910), theyeat tions(see Torres1984). the brood when starvationthreatens, and that workers, There were more interspecificcombats at tuna fish larvaeand queens can oftenendure long periodswithout baitsin non-forestedthan forested areas. I observedcom- food or water(Brown 1973, Carrolland Janzen1973). bats in 6 percent(N = 464) of the baitsput in the forest Stabilityin ant communitiesis also enhancedby the lon- comparedto 38 percent(N = 1056) of those in non- gevityof their members and thefact that the total number forestedareas. This agreeswith Culver's (1974) finding of ants can varywithout altering the numberof colonies of moreprevalent aggression in structurallysimple habi- (Pickles 1940, Wilson 1971). When conditionsimprove tats,but is in disagreementwith his conclusionof lower coloniesserve as nuclei in the rapid restorationof the speces packingin communitieswhere aggressions are more populationsof individuals(Wilson 1971). common.This suggeststhat interspecfic aggression, which Predationdid not appear to be the cause of the dif- is climaticallyinfluenced, plays a greaterrole in the allo- ferencein species numbersand distribution.Ants have cationof resourcesin the non-forestedareas. fewnatural enemies (Wheeler 1910, Skaife 1974, Wil- MacArthur's(1972) suggestionthat habitatswith son 1971). The effectof predatorson workerants is best greaterstructural diversity should have greaternumbers describedas a parasiticrelationship (at the colonylevel) of specieswas not supportedby thisstudy. The forest's due to thesterility of workerants. Worker losses through greaterstructural diversity, acting as a buffer,reduced the foragingmortality are usuallycompensated by theamount numberof climaticmicrohabitats for ants, thus reducing of food taken in exchange(Carroll and Janzen 1973). the numberof ant species.Food overlapswere larger in Antsare the worstenemies of otherants (Wilson 1971), thenon-forested areas, contrary to theexpectation of larg- but the Cerapachyinae, and some Ponerinae er overlapin morepredictable environments (Levins 1968, that are specializedpredators on other ant species are MacArthur1972, May 1973). It is possiblethat overall absentfrom Puerto Rico. overlapswere smaller in thenon-forested areas when food In summary,the greaternumber of speciesin non- overlapsare combinedwith microhabitatoverlaps. The forestedareas is relatedto greaterfood overlaps,tighter difficultiesof comparingmicrohabitats across habitats and guilds,a morevariable microclimate and higherlevels of thenon-independence of theseniche dimensions impeded aggressiveness. the analysesof overalloverlaps. AlthoughI did not carryout experimentsto deter- mine the contributionof area, predationand disturbance ACKNOWLEDGMENTS to the numberof in these it seems species communities, Thismanuscript was adaptedfrom my doctoral dissertation at that these factorsare not responsiblefor the numberof theUniversity of California(Berkeley). I wouldlike to thank species.Greater area could be a factorpermitting more RichardLevins, Daniel Simberloff, Robert K. Colwell,Ana M. species due to its influencein loweringextinction rates Marin,Roy Snelling,Donald Strong, Shahid Naeem, Herbert (MacArthurand Wilson 1967). However,forested areas G. Baker,David Wake,Fabian Jaksic, Lucia GonzMez, Lloyd Goldwasser,Julio Cardona, Rub6n Rodriguez, Manuel Rivera, werelarge enough (in termsof ant biology)to nullifythis Donald H. Teener,Arlee Montalvo, James Ackerman and an effect.In a studyof thebiogeography of antsin thePuerto anonymousreviewer for their help duringthe courseof this Rican bank (Torres,unpublished), I have foundislands work.

302 Torres

This content downloaded from 166.4.81.212 on Thu, 25 Feb 2016 16:07:15 UTC All use subject to JSTOR Terms and Conditions Duringthis study I was partiallysupported by a Ford Foun- Universityof California,and the Departmentof Zoology pro- dation Fellowship.The Centerfor Latin AmericanStudies, the vided traveland computerfunds.

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