Changes in Plant Community Diversity and Floristic Composition on Environmental and Geographical Gradients Author(s): Alwyn H. Gentry Source: Annals of the Missouri Botanical Garden, Vol. 75, No. 1 (1988), pp. 1-34 Published by: Missouri Botanical Garden Press Stable URL: http://www.jstor.org/stable/2399464 Accessed: 02/09/2010 07:33
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http://www.jstor.org Volume75 Annals Number1 of the 1988 Missourl Botanical Garden
CHANGES IN PLANT AlwynH. Gentry3 COMMUNITY DIVERSITY AND FLORISTIC COMPOSITION ON ENVIRONMENTALAND GEOGRAPHICALGRADIENTS 2
' This and thefollowing five papers comprisethe proceedings of theMissouri Botanical Garden's 33rd Annual SystematicsSymposium-Species Diversity. The symposiumtook place in St. Louis, Missouri on October 10 and 11, 1986. 2 I thankthe National GeographicSocietyfor a seriesof grants that supported much of the research summarized here. Collectionof theMadagascar data set was funded by the World WildlifeFund. The coastal Colombianand Ecuadorian data sets and some of the Amazonian Peru data weregathered incidentalto fioristic projects funded by the National Science Foundation. Additional Peruvian data sets werefunded by USAID (DAN-5542-G-SS- 1086-00) and the Mellon Foundation; study of the Tambopata treeplots was in part funded by a grantfrom the SmithsonianInstitution to T Erwin. The data setsfrom eastern Brazil and Paraguay weregathered as part of an NSF-sponsoredmonographic study of Bignoniaceae (BSR 83-05040, BSR 86-07113). The Osa Peninsula, Costa Rica, data were obtained as an OTS class project; the Los Tuxtlas,Mexico, data came from a similar class projectfor the UniversidadNacional Aut6nomade Mexico; parts of the Colombiandata weregathered as a project of the CursoPos-Grado de Botdnica of the UniversidadNacional de Colombia.Among the manyfriends and colleagues who collaborated in gathering the data summarizedhere were R. Neumann, R. Palacios, C. Crist6bal,and A. Schinini (Argentina);K. Kubitzki,M. Fallen, H. Popppendieck, and W. Lippert (Germany); J. Miller,D. Faber-Langendoen,E. Zardini, and C. Burnett (U.S.A.); C. Ramirez (Chile); E. Lott (Mexico); D. Stevens,P. Moreno,and A. Grijalva (Nicaragua); H. Cuadros, E. Renteria,A. Cogollo,M. Monsalve,A. Juncosa, C. Restrepo,J. Ramos, P. Silverstone,and 0. de Benavides (Colombia); C. Dodson (Ecuador); B. Stein, R. G. Troth-Ovrebo,and P. Berry (Venezuela); F. Ayala, C. Dtaz, R. Vasquez, N. Jaramillo,D. Smith,R. Tredwell, K. Young,and D. Alfaro (Peru); A. Peixoto and 0. Peixoto (Brazil); V Vera,J. Ddvalos, and S. Keel (Paraguay); G. Pilz (Nigeria); D. Thomas (Cameroon); L. Dorr, L. Barnett, and A. Rakotozafy (Madagascar); J. Connell and J. Tracy (Queensland); J. Tagai (Sarawak); G. McPherson (New Caledonia); and V Kapos (Jamaica). Additional original data using the same or comparable techniqueswere made available by E. Lott (Mexico), D. Lorence (Mauritius), and J. Miller and P. White (U.S.A.). I also thankR. Perrozzi, S. McCaslin, G. Fulton, and especially J. Millerfor computationaland technical expertise,E. Zardini for help in thefield and withthe illustrations,and J. Hall and D. Thomasfor providingAfrican data. I thankS. Hubbell, T. Givnish,L. Emmons, P. Ashton,P. Raven, and D. Thomasfor reviewcomments. 3 MissouriBotanical Garden,P.O. Box 299, St. Louis, Missouri 63166, and WashingtonUniversity, St. Louis, U.S.A.
ANN. MISSOURI BOT. CARD. 75: 1-34. 1988. 2 Annals of the Missouri Botanical Garden
ABSTRACT
Trendsin communitycomposition and diversityof neotropicalforests as measured by a series of samples of (1) plants 2 2.5 cm dbh in 0.1 ha, (2) plants over 10 cm dbh in 1-ha plots, and (3) completelocal florulas are analyzed as a functionof various environmentalparameters. These trendsare also compared with those found in similar data setsfrom other continents. Altogether the basic 0.1-ha data sets are reportedfor 87 sites in 25 countrieson six continentsand several islands. New data fromten 1-ha treeplots in upper Amazonia are also compared witheach otherand withsimilar data fromthe literature.Some noteworthytrends include: (1) Lowland neotropicalplant species richnessis generallyfar moretightly correlated with precipitation than with edaphic factors. (2). The nearly linear increase of lowland neotropicalplant species richnesswith precipitation reaches an asymptote(community saturation?) at about 4,000 mmof annual rainfall. (3) Althoughthe species representedin adjacent foresttypes on differentsubstrates may change dramatically,diversity- tends to change relativelylittle in upper Amazonia. (4) The species presentat differentsites are verydifferent but thefamilies representedand theirdiversities are highlypredictable from environmental parameters. (5) On an altitudinal gradient in the tropical Andes thereis a sharp, essentiallylinear decrease in diversityfrom about 1,500 m to near the upper limitofforest above 3,000 m. (6) Thereis no indicationof a "mid-elevationbulge" in diversity, at least not in the sampled habit groups. (7) Even near timberline,montane tropical forests are as diverse as the most diverse temperateforests. (8) Moist subtropicalforests are markedlyless diverse than their inner- tropical equivalents,but dry subtropicalforests in Mexico are apparently richerin species than inner-tropical dryforests. (9) CentralAfrican forests are about as species rich as neotropicalforests with similar amountsof precipitation,but forests in tropical WestAfrica are relativelydepauperate. (10) Tropical Australasianforests are no more diverse than equivalent neotropicalforests; the world's highest tree species diversity-is in upper Amazonia, not Southeast Asia. (11) Contraryto accepted opinion, equivalentforests on the three continents are similar in plant species richness and (with a veryfew notable exceptions) fioristiccomposition but are markedlydifferent in structure.The predictabilityof thefioristic compositions and diversitiesof tropicalforest plant communitiesseems strong,albeit circumstantial,evidence that these communitiesare at ecological and perhaps evolutionaryequilibrium, despite indicationsthat certain aspects of theirdiversity are generated and maintainedstochastically.
Comparisonsof the species richness (or have reportedthe firstcomparable data set otherfacets) of differentforests or different fortropical forests (Gentry & Dodson, 1987a, vegetationtypes are oftendifficult because of b). A standardizedsampling technique that the dissimilarityof the availabledata. In trop- includesonly plants - 2.5 cm in diameterin ical Asia there is a wealthof data for trees 0.1 ha has also been developed and applied in largesample areas (Ashton,1964, in press; to a seriesof tropicalforests (Gentry, 1982b, Whitmore,1984; Proctoret al., 1983; Kar- 1986b; Lott et al., 1987; Stallingset al., in tawinataet al., 1981) but fewpublished data press; Lorence & Sussman, 1988); the on nontrees. In the Neotropics there are methodologyfor obtaining these O. -ha sam- several local florulas(Croat, 1978; Dodson ples, each the sum of ten 2 x 50 m belt & Gentry,1978; Janzen& Liesner, 1980; transects,is discussed in detail elsewhere Dodson et al., 1985), but untilrecently there (Gentry,1982b, in prep.). The primarydata have been no tree-plotdata fromhigh diver- set on which this paper is based are these sityregions based on reliableidentifications. 0.1-ha samples,which are now available for Africahas far more extensivecoverage by 38 lowlandneotropical sites, 1 1 montaneneo- regionaland country-widefloras but no local tropicalsites, and 13 subtropicaland 9 tem- florulasnor large-plotdata fromhigh-diver- perate-zonesites in theAmericas. Similar data sityregions. sets are available from6 sitesin tropicalAf- Recently,a series of 0.1-ha samples of rica, 3 sitesin tropicalAustralasia, 2 sitesin manyof the world'smost diverse extra-trop- Europe,and fromseveral tropical islands: New ical plantcommunities has been accumulating Caledonia, Madagascar, Mauritius,Jamaica (e.g., Naveh & Whittaker,1979; Cowling, (Tables 1, 2; Fig. 1). Supplementarydata are 1983; Peet & Christensen,1980; Rice & taken fromlocal florulasin the Neotropics Westoby,1983; Eiten, 1978). Elsewherewe (Dodson& Gentry,1978,1988; Croat,1978; Volume 75,-Number1 Gentry 3 1988 Plant CommunityDiversity
FIGURE 1. Locations of study sites. Dots = 0.1-ha samples (see Tables 1, 2). Arrows= local fiorulas. For location of 1-ha treeplots see Gentry,1988.
Janzen& Liesner,1980; Dodsonet al., 1985; so tightlycorrelated (R2 = 0.93) with the Hammel,pers. comm.(La Selva, Costa Rica)) absolutenumber of species that their use would and fromthe Makokou region of northwestern add littleto the analysis.Moreover, the wet- Gabon (Halle, 1964, 1965; Halle & Le forestH' values of 7 to 8 are far above the Thomas, 1967, 1970; Florence & Hiadik, levels at whichH' has been statisticallyana- 1980; iladik & Halle, 1973; Hladik & Gen- lyzed (cf. May, 1975). try,in prep.). A supplementaldata set is pro- videdby a seriesof 1-ha tree plotsin various TEMPERATE-TROPICAL PATTERNS partsof the Neotropics (Gentry, 1988; Prance et al., 1976; Campbellet al., 1986; see also Figure2 summarizesthe latitudinaltrends Gentry,1982b) and Paleotropics(e.g., Ash- in species richness,based on the 74 lowland ton, 1964, 1977, in press; Gartlan et al., (= < 1,000 m) 0.1-ha sites forwhich com- 1986). parablesamples are available.It is wellknown Here I firstreview how the species richness that tropicalforests are generallyfar richer ofplant communities changes on fivedifferent than temperateforests in species (e.g., see environmentalgradients: latitudinal, precipi- Richards,1952; MacArthur,1972). Figure tational,edaphic, altitudinal,and interconti- 2 indicatesthat for vascular plants species- nental. Observationson a few noteworthy richtropical forests are typicallyan orderof trendsin foreststructure are also included. magnitudemore diverse. Also apparent in Second, I analyze some patternsof floristic Figure 2 are several much less well-known change along the same environmentalgra- corollariesto the generallatitudinal diversity dients. Finally,I use these analyses to ex- gradient.1) The differencein speciesrichness aminebriefly the questionof whysome plant betweendifferent tropical forests is fargreater communitieshave so manymore species than than the differencebetween temperate zone others. and species-poortropical forests.Whereas In all of these analyses I willuse number the temperateforest samples have 15-25 of species as the simplestand most appro- species and tropicaldry forestones mostly priatemeasure of diversity,as suggestedby 50-60 species,the samplesof moistand wet Whittaker(1977). Shannon-WienerH' val- tropical forestsaverage about 150 species ues are reportedin Tables 1 and 2, but are and pluvialforests over 250 species (Gentry, 4 Annals of the Missouri Botanical Garden
TABLE 1. Site characteristicsfor 0.1-ha samples.
Num- Alti- Precipi- ber of Grid tude tation Fami- Numberof Site Coordinates (i) (mm) lies Species H' Reference TemperateNorth America BurlingTract, Virgin- 38055'N 30 1,053 12 21 3.54 Givnishet al., ia 77010'W unpubl. NorthwestBranch, 39002'N 20 1,060 14 20 3.22 Maryland 77002'W Tyson Reserve,Mis- 38030'N 150 932 12 23 3.26 Zimmerman& souri(oak woods) 9003 lW Wagner, 1979 Tyson Reserve,Mis- 38030'N 150 932 11 25 3.68 Zimmerman& souri(chert glade) 90031'W Wagner, 1979 Babler State Park, 38032'N 150 930 13 21 3.61 Missouri 90040'W CuivreRiver State 39?01'N 140 930 15 26 3.46 Park, Missouri 91000'W Valley View Glades, 38015'N 225 930 14 22 3.68 Missouri 90037'W Indian Cave State 40030'N 320 900 12 23 3.74 Tate, 1969 Park, Nebraska 95043'W Great SmokyMoun- 21-30 White, 1983 tains National (upper 5%) Park, Tennessee/ N.C. Europe Siiderhackstedt,West 54?N 20 695 10 15 2.19 Walter & Lieth, Germany 1H1E 1960 AllacherLohe, West 48004'N 530 866 11 20 3.41 Walter & Lieth, Germany 1 1?'30'E 1960 Temperateand SubtropicalSouth America Rio Jejui-mi,Para- 24042'S 150 1,800 31 85 5.40 S. Keel & V. guay 55030'W Vera, pers. comm. Parque El Rey, Ar- 24045'S 1,000 1,500 27 40 4.18 Brownet al., gentina 64040'W 1985 Salta, Argentina 24040'S 1,300 712 16 25 3.41 Walter & Lieth, 65030'W 1960 ArroyoRiachuelo, 27030'S 60 1,200 27 47 4.46 Walter & Lieth, Corrientes,Argen- 58050'W 1960 tina Alto de Mirador,Chile 40014'S 800 4,000 13 16 3.45 Ramirez& Ri- 73018'W veros, 1975 Bosque de San Mar- 39030'S 30 2,316 14 18 3.25 Riveros& Ra- tin,Chile 73?10'W mirez,1978 Puyehue National 40043'S 500 3,000 13 16 2.41 Munioz,1980 Park, Chile 72018'W "Subtropical"Central Amierica Chamela, Mexico 19?30'N 50 733 37 92 5.76 Lott et al., 1987 105?03'W Volume 75, Number1 Gentry 5 1988 Plant CommunityDiversity
TABLE 1. Continued.
Num- Alti- Precipi- ber of Grid tude tation Fami- Numberof Site Coordinates (i) (mm) lies Species H' Reference
Chamela, Mexico 19030'N 50 733 34 83 5.42 Lott et al., 1987 105003'W Chamela,Mexico 19030'N 50 733 46 105 5.9 Lott et al., 1987 105003'W Los TuxtIas,Mexico 18035'N 200 4,953 40 108-109 4.52 Lot-Helgueras, 95008'W 1976 Cerro Olumno,Nicara- 12018'N 750 2,000 36 97-98 5.8 - gua 85024'W Cerro El Picacho, 13000'N 1,400 2,000 39 65 5.22 - Nicaragua 85055'W LowlandNeotropics (12?N to 12?S, ' 1,000 m) Corcovado,Costa Rica 8030'N 30 3,800 46 132 6.56 Hartshorn, 83035'W 1983 Guanacaste (upland) 10030'N 100 1,600 21+ 53a Hartshorn, Costa Rica (700 z 8501O'W 1983 m2) Guanacaste(gallery), 10030'N 50 1,600 33+ 68a Hartshorn, Costa Rica (800 ; 85010'W 1983 m2) Curundu,Panama 8059'N 20 1,830 42 90 5.78 Gentry,1982b 79033'W Madden Forest,Pana- 9066'N 50 2,433 45 126 6.34 Gentry,1982b ma 79036'W PipelineRoad, Pana- 901O'N 300 3,000 58 167 6.77 Gentry& Em- ma 79045'W mons, 1987 Galerazamba,Colom- 10048'N 10 500 21 55 5.05 - bia 75015'W Tayrona,Colombia 11020'N 50 1,500 31 65 5.36 - 74002'W Bosque de la Cueva, 11005'N 360 2,000 36 93 5.5 - Colombia 73028'W Tutunendo,Colombia 5046'N 90 9,000 53 258 7.57 Gentry,1986b 76035'W Bajo Calima, Colombia 3055'N 100 7,470 58 265 7.74 Gentry,1986b 77002'W Boca de Uchire,Ven- 10009'N 150 1,200 20 66 5.16 Gentry,1982b ezuela 65025'W BlohmRanch, Vene- 8034'N 100 1,400 31 68 5.38 Troth,1979 zuela 67035'W Estaci6nBiol6gico de 8056'N 100 1,312 21+ 59a Gentry,1982b los Llanos, Vene- 67025'W zuela (500 m2) Cerro Neblina,Vene- 0050'N 140 3,000 31 97 5.33 zuela (No. 1) 6601?'W Cerro Neblina,Vene- 0050'N 140 3,000 26 83 4.95 zuela (No. 2) 66?11'W Rio Palenque, Ecua- 0?34'S 200 2,980 50 119 6.15 Dodson & Gen- dor (No. 1) 79?20'W try,1978 6 Annals of the Missouri Botanical Garden-
TABLE 1. Continued.
Num- Alti- Precipi- ber of Grid tude tation Fami- Numberof Site Coordinates (i) (mm) lies Species H' Reference
Rio Palenque, Ecua- 0034'S 200 2,980 43 121 6.18 Dodson & Gen- dor (No. 2) 79?20'W try,1978 Centinela-,Ecuador 0034'S 550 3,000 55 140 4.78 Gentry,1986b 79018'W Jauneche,Ecuador 1016!S 60 1,855 38 96 5.39 Dodson et al., 79042'W 1985 Capeira, Ecuador 2000'S 50 804 26 60 5.41 Dodson & Gen- 79058'W try,1988. INPA, Manaus, Brazil 30S 75 1,995 34 101 Gentry,1978 60?W Mocambo,Belem, 1?30'S 30 2,760 39 131 6.42 Pires & Prance, Brazil- 47059'W 1977 Linhares,Espirito 19018'S: 50 1,403 53+ ca. 212 7.4 Peixoto& Gen- Santo, Brazil 40?04'W try,in prep. Jacarepagua,Rio de 23?05'S 200 1,500 45+ ca. 160 Janeiro,Brazil 43025'W Tarapoto,Peru 6040'S 500 1,400 38 97 5.96 76020'W Sucursari,Peru 3015-S 140 3,500 46+ ca. 240' 7.46 72055-'W Yanamono,Peru (up- 3028'S 140 3,500 50 212 7.49 Gentry& Em- land)z(No. 1) 72050'W mons, 1987 Yanamono,Peru (up- 3028'S 140 3,500 50 225 7.59 Gentry& Em- land) (No. 2) 72050'W mons, 1987 Yanamono,Peru (ta- 3028'S 130 3,500 51 163 6.67 huampa) 72050'W Mishana,Peru- (flood- 3047S 130 3,500 58 249 7.63 Gentry& Em- plain) 73030'W mons, 1987 Mishana,Peru (ta- 3047S 130 3,500 40 168 6.44 huampa) 73030'W Mishana,Peru (upland 3047S 140 3,500 46 196 7.21 Gentry& Em- whitesand) 73030'W mons, 1987 Bosque von Humboldt, 8050'S 270 2,500 44 154 6.37 Peru 75000'W Cabeza de Mono, 10020'S 320 3,500(+) 42 147 6.82 Gentry,1988 Peru 75018'W Cocha Cashu, Peru 1105I'S 400 2,000 49 162 6.78 Gentry& Ter- 71019'W borgh,in press Tambopata,Peru (lat- 12050'S 260 2,000 48 149 6.7 Erwin,1985 eriticterra firme) 69017'W Tambopata,Peru 12050'S 260 2,000 43 130 6.44 Erwin,1985 (sandyterra firme) 69017'W Africa Makokou,Gabon (No. 0034'N 500 1,755 39 135 6.44 Hladik,-1978 1) 12?52'E Makokou,Gabon (No. 0?34'N 500 1,755 32 116 6.25 Hladik, 1978 2) 12?52'E Volume 75, Number1 Gentry 7 1988 Plant CommunityDiversity
TABLE 1. Continued.
Num- Alti- Precipi- ber of Grid tude tation Fami- Numberof Site Coordinates (m) (mm) lies Species H' Reference
Omo Forest,Nigeria 7?N 50 1,800 29 73 4.42 Richards,1939 50E Oban Forest,Nigeria 5010'N 50 4,000 ? (53++) (200 m2) 8028'E Mt. Cameroon,Cam- 4?N 230 8,000 37 129 6.31 Richards,1963 eroon 90E Korup NationalPark, 5?N 50 5,460 43 139 6.34 Gartlanet al., Cameroon 8031'E 1986 Belinga,Gabon (500 1?N 750 1,800 26(+) 115 Aubreville,1967 m2) 140E Perinet,Madagascar 18055'S 950 1,200 52+ ca. 199 48025'E Australia Davies RiverState 17005'S 800 2,300 41 115 6.29 Connellet al., Park, Queensland 145034'E 1984 Asia SemengohForest, Sa- 1050'N 20 4,000 47 243 7.39 Walter & Lieth, rawak 110005'E 1960 Bako NationalPark, 1052'N 30 4,000 39 143 6.5 Ashton,in press Sarawak 110006'E Tropical Islands Rivieredes Pirogues, 222010'S 360 2,200 47 151 6.31 New Caledonia 166050'E Round Hill,Jamaica 17050'N 40 1,200 31 58 3.96 Kapos, 1982 77015'W (4.47) Brise Fer, Mauritius 20030'S 600 2,400 26 61 Lorence & Suss- 57030'E man, 1988
aExtrapolated fromnumber of species in sample of < 1,000 M2.
1986b). 2) The latitudinaldecrease in species 4) Species-poortropical forests with single- richnessseems to be asymmetricalabout the species dominanceare generallystill much equator;in theSouthern Hemisphere it begins morediverse than any temperate-zoneforest. near theTropic of Capricorn, but in the north 5) South temperateforests, at least in Chile, it begins well inside the Tropic of Cancer, where data sets are available, have fewer apparentlynear 12'N latitude.3) Temperate speciesthan temperate forests in NorthAmer- zone forestsare very similarin species rich- ica, contraryto the popularperception of the ness ofwoody plants, compared with the mas- "rich" Valdivianforest; a major reason for sive differencesin species richnessbetween this differenceis that Valdivian forestsdo temperateand tropicalforests or betweendif- not have sympatriccongeners like the up to ferenttropical forests. Temperate zone forests seven Quercusand fourCarya species typical are so massivelydepauperate that even if of 0.1 -ha samplesof easternNorth American borealforests with two or threespecies ' 2.5 forests.6) Subtropicaldry forestscan have cm dbh in 0.1 ha were includedin Figure 2, morespecies thando full-tropicaldry forests, they would not significantlychange it, even even thoughwet or moistforests usually have thoughthe reportedvalues are for some of fewerspecies in the subtropicsthan in the the reputedlyrichest temperate zone forests. innertropics. 8 Annals of the Missouri Botanical Garden
TABLE 2. Site characteristicsfor 0.1-ha samples from upland Neotropics (2 1,000 m, 12"N to 120S). Parenthesesindicate sites too incompletelysampled for a meaningfulestimate of numberof species in 0.1 ha.
Median Grid Altitude Numberof Numberof Site Coordinates (m) Families Species H'
(Monteverde,Costa Rica (200 m2)) 10048'N 1,550 (33+) (61+) 84050'W
Cerro Kennedy,Colombia (500 M2) 1105'N 2,600 26 5Oa 4.92 74001'W (Cuchillode Sap Antonio,Colombia (200 M2)) 10058'N 1,710 (15+) (24+) 73030'W
Finca Zungara,Colombia (600 M2) 3032'N 1,990 37+ 1OOa 76035'W Farallonesde Cali, Colombia 3o30'N 1,950 55 134-135 6.48 76035'W Finca Mehrenberg,Colombia 2016'N 2,290 40 107 4.46 76012'W La Planada, Colombia 1010'N 1,800 38 116 5.14 77058'W
Pasochoa, Ecuador (400 m2) 0028'S 3,010 21 28a 3.03 78025'W Venceremos,Peru 5045'S 1,850 46 159 6.65 77040'W Incahuara, Bolivia 15055'S 1,540 45 130 6.71 67035'W Sacramento,Bolivia 16018'S 2,450 32 93 4.89 67048'W
aExtrapolated fromnumber of species in sample of < 1,000 M2.
There are also latitudinaldifferences in precipitation(Gentry, 1 982b). However,this foreststructure. In general,tropical forests, relationshipis more complexthan originally far frombeing open and cathedral-like,are suggested(Gentry, 1982b), and the correla- denserthan temperate forests. This difference tionmay not exist at all in the Paleotropics. is almostentirely due to small-diameterplants, In tropicalAsia, high rainfallareas such as lianas, and trees less than 10 cm dbh (also Mt. Cherrapunji,Assam, often have relatively see Gentry,1982b). Biomass(as extrapolated low plantspecies richness(Ashton, in press). frombasal area) is roughlyequivalent among' In tropicalAfrica, two high rainfallsites (> differenttropical forests (X= 34.9 m2/ha, 5,000 mm per year) in southwesternCam- N = 36 (excludingAfrica; X= 70.7 m2/ha, eroon(Korup, Mt. Cameroon)have onlymar- N = 6)) and northtemperate deciduous forests ginallymore species in 0.1-ha samples than (X = 29.6 m2/ha, N = 5) but markedly do samplesfrom northeastern Gabon thatre- greaterin the Valdivianforests (X= 155.7 ceive < 2,000 mm of annual rainfall.More- m2/ha,N = 3) as well as in theirnorth tem- over,a moremonsoonal climate site in Nigeria perate equivalent,the northwesternconifer- (Omo Forest) had many fewerspecies than ous forests(Waring & Franklin,1979). the Gabon sites despite having similarpre- cipitationvalues. Thus, it seems likelythat the generalizationthat diversity increases lin- DIVERSITY VS. PRECIPITATION early withprecipitation (Gentry, 1982b) ap- In the Neotropics,plant species richness pliesonly in thespecial case ofthe Neotropics, is stronglycorrelated with absolute annual where total annual rainfalland strengthof Volume 75, Number1 Gentry 9 1988 Plant CommunityDiversity
300,
200
en:0 :
E
100 _'
40 30 20 10 0 10 20 30 40 50 OS Latitude ON
FIGURE 2. Species richnessof 1,000 M2 samples of lowland (< 1,000 m) forestas a functionof latitude. Closed line enclosescontinental African points; dottedline enclosesAsian points;dash-dot line enclosesAustralian and New Caledonian samples; other tropical and subtropicalpoints all neotropical except anomalously high diversityMadagascar point at 190S, (circled). Dashed line separates dryforest (bottom)from moist and wet forest (top) with three intermediatesites (moist forest physiognomydespite relativelystrong dry season) indicated by alternatelines.
the dryseason are stronglycorrelated. A po- mm of annual precipitation (Fig. 3). The re- tentialtest of the relativeimportance of dis- lationship is significantly curvilinear (F = tributionand amountof precipitationcomes 4.299, P < 0.05). From 4,000 mm to near from a single 0.1-ha site in coastal Brazil the wettest place in the world (Tutunendo, (Linhares), which has the unusual (for the Colombia) there is little or no change in the Neotropics)condition of low, evenly distrib- species richness of neotropical plant com- uted annual rainfall.Although analysis of the munities as measured by the 0. 1-ha sampling Linharesdiversity data is not completed(Pei- protocol. The regularity of species richness xoto & Gentry,in prep.) and the site is thus patterns, and especially the apparent lid on not includedin Figure3, it is obviousthat its community richness suggested by this as- estimated212 species in 0.1 ha are farmore ymptote,seem strongcircumstantial evidence than would be expected fromits 1,400 mm of the kind that zoologists (e.g., MacArthur, of annual precipitation. 1965, 1969) have construed as representing While the manyadditional 0.1-ha samples niche saturation and community equilibrium. now available fromthe lowland Neotropics It is also possible that part of the apparent generallystrengthen the previouslyreported lid on plant community richness merely re- relationshipbetween neotropical plant species flects the intrinsiclimitations of the sampling richnessand precipitation(Gentry, 1982b), technique. Figure 4 compares the accumu- additionaldata sets at the upper end of the lation of species with sample area for several precipitationscale stronglyindicate that the representative sites. In low-diversityforests relationshipbecomes nonlinear,reaching a the species area curves level off below 500 marked asymptoteat around 4,000-4,500 m2 indicating that most of the species present 10 Annals of the Missouri Botanical Garden
300 -
250
Q 200 -
a
0 150 W E
1 2 3 4 5 6 7 8 9
Annual precipitation (mm x 103) FIGURE 3. Numbersof species in 0.1-ha samples of lowland neotropicalforest vs. annual precipitation.Solid line = straightline regressionfor sites with < 5,000 mmannual precipitationwith visually estimatedasymptote. Dashed line = computergenerated curve: y = 12.37 + 0.0613x - 0.000003598x2. The curve is displaced slightlyupward from the data points,since questionablemorphospecies and lost specimensare treatedas distinct species by the computerwhile the data points representbest estimatesof species numbers.Data from Table 1 with subtropicalsites excluded. in a givencommunity have been sampled,but thersupported by preliminarydata from1-ha in species-richvegetations the species-area treeplots in upperAmazonia (Gentry, 1988). curvesshow little sign of leveling off. To what In these samples only trees and large lianas extenta larger samplingarea mightreveal - 10 cm in diameterwere censused(Fig. 5). significantdiversity differences between the The two mostspecies-rich sites are fromthe differenthigh rainfall sites remains unknown. everwet high rainfall (3,000-4,000 mm) The strongrelationship of species richness Iquitos area of northernAmazonian Peru, to precipitationin neotropicalforests is fur- wherediversity reaches almostridiculous ex-
300 Bajo Calima Tutunendo 250 a 200* /.Yanamono 2 200
-E 150 z 100 _ _ Tarapoto
50______....BlohmRanch 50 *
_ _ - .Northwest* . * * *Branch
1 2 3 4 5 6 7 8 9 10 Transect number
FIGURE 4. Species-area curvefor 100 m2 subsamplesof representative high- and low-diversity0.1-ha samples. Volume 75, Number1 Gentry 11 1988 Plant CommunityDiversity
800
Relatively Poor soil 700 fertile soil
(av. 19.6/ha.) 60'0 0.ianas *; *F- . : Etrees< 30 cm dbh
3treesat= 30 cm dbh rich S soil av.: 106.7/ha 500 poor soil av.: 81/ha E
0.
All 400-
CoC'
300 S ~~~~0 2
FIGUE6 mer c a Coa COO C C 10 diameter..0c E *0~~0ao 0 0 0 N Co .0 E E E M
100
FIGURE 5. Density of trees and large lianas in 1-ha Amazonian plots. Black= lianas; hatched= trees > 30 cm dbh; white =treeso 10-30 cm dbh. K~~~~~~~~~~~C1 w
Aseasonal 300
250 Co Couva CobptMn uln ~ Dry~ Season Subtropical
200 a ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~CO 0 ~~~~~~~~~~~~~~~~~~~~0 0. CO - 1,50 0~~~~~~~~~~~~~~~~~~~ E E z 100
50
Yanamono Mishana Manu Cabeza de Tambopata Tambopata INeblina Mono alluvial Tambopata upland 2 12 Annals of the Missouri Botanical Garden
tremes(Fig. 6). At Yanamono thereare 300 1977, in press; Gartlanet al., 1986). These species - 10 cm in diameterout of the 606 authorssuggest that phosphorus, magnesium, individualplants in a hectareplot! The other and potassiumare amongthe nutrientswhose 1-ha plots in AmazonianPeru are in areas levels are moststrongly correlated with trop- withgenerally greater dry season stressand ical plantcommunity diversity. Nevertheless, less overall precipitation.Two sites between at least in the Neotropics,soil nutrientsare 100 and 12S latitudehave about 200 species farless importantthan biogeographicfactors - 10 cm dbh, while several 1-ha plots in or precipitationin determiningplant species differenthabitat types at TambopataReserve richness(Gentry, 1982b; Stark et al., sub- in southeasternMadre de Dios (1 2050'S) have mittedms.). Multipleregression of a seriesof between 153 and 181 species. Thus tree 31 lowlandneotropical sites for which we have species richnessalso appears to be greatest both soil and species richnessdata for 0.1- in aseasonal highrainfall areas, at least within ha samples produced the equation: Species Amazonia. Richness= 84.48 + 0.025(mean annual Epiphyte diversitylikewise increases in precipitation)- 0.1 00(extractable soil K). wetterareas. While epiphytescan be well R2= 0.76, N = 31 (Stark et al., submitted representedin areas withhigh atmospheric Ms.). humiditybut relativelylow rainfall,our data Thus our data indicate that the nutrient indicatethat absoluteprecipitation is gener- most closely correlated with neotropical ally a remarkablygood predictorof epiphyte species richnessis K. The importanceof K diversity(Gentry & Dodson,1987b). We have agrees with what Ashton (1977, in press) data sets froma series of local florulasin foundfor a largeseries of tree plots in Borneo, westernEcuador and southernCentral Amer- Gartlanet al. (1986) also foundavailable K ica; epiphytesvary from9-24 species (2- to be highlyand significantlycorrelated with 4% of the total flora)in dry-forestsites to floristicdiversity in a series of sites in Cam- 72-216 species (12-16% of the total flora) eroon.Our data contrastwith those of Ashton in moist-forestsites to 238-368 species (23- (1977, in press) and Gartlanet al. (1986) in 24% of the total flora) in wet-forestsites thatwe do not findphosphorus to be strongly (Gentry& Dodson, 1987a, b). For a series correlatedwith diversity. This may be due in of 1,000 m2samples in whichall plantspecies part to differenttechniques of nutrientex- wereidentified and tabulatedin threewestern traction(ammonium acetate vs. HCl). It is Ecuadorian forests,3 epiphytesconstituted also relatedto the factthat the mostspecies- 2% ofthe species in a dryforest, 13 epiphytes rich 0.1-ha sample (Bajo Calima, Colombia) constituted8% ofthe species in a moistforest, comes froma peculiarwhite clay soil with0 and 127 epiphytesconstituted 35% of the phosphorusas measuredby our technique. species in a wet forest(Gentry & Dodson, Whereas Ashton's(in press) data sets in- 1987b). The wet forestat Rio Palenque is so dicate greatestdiversity at intermediatenu- diversein plant species that,even excluding trientvalues, a "humped" nutrient/diversity tree species, it has more species of herbs curvethat fits the modelproposed by Tilman (includingherbaceous epiphytes) or of shrubs (1982, 1984), I see no indicationin my data in 0.1 ha than any nontropicalplant com- of a general decrease in diversityon richer munityin the -world (Gentry & Dodson, soils in the Neotropics.Quite the contrary, 1987a). the most species-richtree plot in the world at Yanamono, Peru, is on relativelyrich soil (Gentry,1988; Stark et al., submittedms.); DIVERSITY VS. SOIL NUTRIENTS furthersouth, in an area witha strongdry There has been much recent interestin season, the 0.1-ha Cocha Cashu sample on therelationships between tropical soil nutrient unusuallyrich alluvial soil is fartherabove levelsand plantcommunity richness (Ashton, theprecipitation-diversity regression line than Volume 75, Number1 Gentry 13 1988 Plant CommunityDiversity
200
150 A!---1 white sand (Mishana & Neblina) subtropical (Tambopata) tropical terra firme (Yanamono, ManO, & Cabeza de Mono)
o 1 00,
E
50
1 2 3 4 5 6 7 8 9 '10 number of individuals FIGURE 7. Numberof individuals/speciesin 1-ha Amazonian treeplots (plants 2 10 cm diam.). any othersite (Gentry,1985a). My data do ridge system tropical-subtropicaldemarca- fitwell withAshton's along the low nutrient tionhave fewerspecies than the full-tropical end of the diversity-soilnutrient gradient, ones on eitherrich or poor soils. Moreover, where there is a generalincrease in species the site withthe most nutrient-poorsoil of richnessfrom nutrient-poor to intermediate all, Cerro Neblina, on pure whitesand, has sites, contraryto the suggestionsof Huston manyfewer species than do any of the other (1979, 1980). sites.Thus the Amazoniantree plotdata gen- Anotherway of comparingthe effectsof erallysupport the idea thatrelatively rich soil soil fertilityon diversityis by comparingoth- correlateswith relative richness in tree species. erwise approximatelymatched site pairs on Especiallynoteworthy in the contextof the fertileand poor soils. The series of six tree relativeimportance of soil nutrientsand pre- plotsin AmazonianPeru fallinto three natural cipitationas determinantsof species richness groupsbased on latitudeand strengthof the is the seriesof 0.1-ha samplesfrom different dry season (Gentry,1988). Of the two plots substratesin the Iquitos area (Table 3). All in the everwetIquitos area, one on rich soil of the sites have the high species richness has (marginally)more species than a nearby (168-212 species) that would be expected siteon whitesand; on a species per individual (Gentry,1982b) in a regionwith high rainfall basis the differencewould be much stronger and no dry season. While samples fromthe (Figs. 7, 8). Of two sites fromcentral Peru, forestssubjectively judged likelyto be sub- the one on richalluvial soil (ManuiPark) has jected to greater stress (i.e., seasonally in- morespecies than one on poorsoil (Iscozacin). undated tahuampa or white-sandcampina- Severalplots at Tambopatasouth of the Hold- rana) have slightlylower species richness,all 14 Annals of the Missouri Botanical Garden
% of species with numberof individuals tion,when such broader-scalebiogeographic factorsas latitudeand altitudeare controlled. This relationshipwould predict that the high- 100_ A est neotropicala-diversities should be found in upper Amazonia,where the soils are rel- withthose of compar- 80 ' .0 ( ativelyrich, compared ablyhigh rainfall areas ofthe Guayana Shield. My data for0.1 -ha samplesand for 1-ha tree 60 _::::::::: : plotsboth appear to fitthis prediction. More- over,many other kinds of organisms,includ- ingbirds, reptiles and amphibians,butterflies, 40 0_._ ., and bats, appear to show excactlythe same pattern of greatest diversityin areas with relativelyfertile soils near the base of the Andes, suggestingthat this relationshipis a generalbiogeographic trend (Gentry, 1988). It is possiblethat increased productivityon
is O the generallyricher soils of thisregion makes O co o (S (U 0 > C c n e 2 XC(U niche and special- E ; a ofz possiblefiner partitioning E /D Co mU (U Co -a _ izationin otherwisemarginal habitats (cf. Em- (U 0 0 mons, 1984; Gentry& Emmons, 1987). (U Even thoughthe effectof soil nutrientson (UE.0 E E Y a-diversitymay be relativelyminor, soil nu- trientsundoubtedly do play a major role in FIGURE 8. Percentof species withdifferent numbers of individuals in Amazonian tree plots (plants - 10 contributingto the high overall diversityof cm diam.). Lower white bar = 1 individual; dotted Amazonian foreststhrough their effecton bar = 2 individuals;hatched bar = 3 individuals;black A-diversity(e.g., Gentry,1981, 1986a, c). bar= 10 or more individuals. Note that an average across all plots of 50% of the species are represented Much ofupper Amazonia, probably more than by single individuals. any other part of the lowland Neotropics, constitutesa conspicuoushabitat mosaic, with verydifferent sets of plantspecies occurring sites are very diverse compared with mois- in adjacent communitieson differentsub- ture-stressed sites with a strong dry season strates(Salo et al., 1986; Gentry,1986a, c). or low annual precipitation. Table 3 shows how littleoverlap in species I conclude that the species richness of neo- thereis betweendifferent, more or less equally tropical plant communities generally in-, diverse plant communitieson differentsub- creases with soil fertilityand with precipita- stratesin the Iquitosarea. Only3-24 species
TABLE 3. Numberof species shared by 1,000 m2 samples of Iquitos area foresttypes.
Mishana Yanamono Yanamono Yanamono Mishana Campi- Mishana No. 1 No. 2 Tahuampa Lowland narana Tahuampa Yanamono Terra firmeNo. 1 212 91 20 24 12 14 Terra firmeNo. 2 230 20-21 19 9 8 White-watertahuainpa 16-3 9 5 ca. 19 Mishana Lowlandnoninundated 249 55 17 Canmpinarana(white sand) 196 3 Black-watertahuampa 168 Volume 75, Number1 Gentry 15 1988 Plant CommunityDiversity
Laguna Cocococl-ha km5 18 spp, shared by plots 3, 4, and 67 co
o poor soil terra firme forest
| | 1 ~~0 o\ld on sandy river terrace/
0 )/?/ < ~~~terafirmet
0 32 spp. shared ~ ~ 27 pp shre
FIGURE 9. Location of 1-ha treeplots in the Tambopata WildlifeReserve, Madre de Dios, Peru. Indicated species numbersfor plots 2 and 5 are approximatesince sampling is notyet complete.Plot 1 data in part based on field identificationsof Gary Hartshorn (pers. comm.),and the actual numberof species will undoubtedlybe higheras well. Shared species indicated onlyfor plots (3, 4, 6) completelysampled and identifiedby me.
out of the ca. 200 species sampled for any of eitherpoor soil plot were shared witha habitat are shared by a differentadjacent nearbytree plot on rich alluvial soil (coeffi- habitat. The one exception is the Mishana cients of correlationof 10-11%'o) (Fig. 9). white-sandand floodplainsamples (55 species Incompletelyanalyzed data foradditional plots overlap),but thesetwo vegetation types have in otherforest types at Tambopata indicate similarsubstrates and are not very well dif- thatthey, too, will show little overlap in species ferentiated.While some of this lack ofoverlap withsandy soil or alluvialforests. The unique- mightbe due to inadequacy of the sampling ly high species richnessof the Tambopata techniquein such diverseplant communities, reservefor such well-knowngroups as birds a repeat sample of the same forestat Yan- (Donahue et al., in press)and butterflies(La- amono gave a much greater, almost 50% mas, 1985) has been suggestedas largelydue overlapin species; in otherspecies-rich moist to thereserve's habitat diversity, a conclusion and wet forestssimilar repeat samplesof the that clearly accords withthe botanical evi- same vegetationalways give the same ca. dence. 50% overlap in sampled species (Gentry, Thus the high species richnessof woody 1982b), contrastingstrongly with the < 20% plantsin Amazoniaas comparedwith the rest overlapsbetween different communities. Sim- of the Neotropics(Gentry, 1982a) is largely ilarly,for two 1-ha tree plots on terra firme /-diversitydue to habitatspecialization. Typ- foreston poor sandy soil at Tambopata, 83 ically,related species may fillsimilar niches species(46% ofthe 181 species in plot 1 and in forestson differentupper Amazoniansub- 48% ofthe 172 speciesin plot2) wereshared strates(Gentry, 1981, 1986c). Dramaticdif- withthe other plot, for a coefficientof as- ferencesin specificcomposition, though not sociationof 44%. Only16- 18% ofthe species intracommunitydiversity, accompany spe- 16 Annals of the Missouri Botanical Garden
Decrease in diversity with altitude
200
180 lowland Amazonian average
160 *Venceremos
moist & wet forest n average Incahuara 140 Centinela Farallones
La Planada 120 * *Finca Zingara
* Los Tuxtlas Merenberg 100 * Cerro Olumo , en Id \\ All\ ~~~~~** SacramentoScmn '-Chamela average
e 80 ' XII 0
*Cerro El PiCsaco E ---dry forest average \
Cerro Kennedy
40 * Parque El Rey Most diverse \ temperate site Salta
Eastern North America average Paaochoa 20 Temperate average 'a Valdivian average % Suderhackfested
0 1 2 3
Altitude in kms. FIGURE 10. Species richnessof 0. 1-ha samples vs. altitude.Points to rightof dashed line and the calculated regressionare for Andean sites. Comparativedata ftom otherselected sites to leftof dashed line. Stars are for individual temperateand subtropicalsites: Sdderhackfestedtis in Germany;Salta and Parque El Rey are in northwestArgentina; Los Tuxtlas is in Veracruz,Mexico; CerroOlumo and CerroEl Pichaco are in Nicaragua; Centinela is an isolated ridge west of the Andean Cordillera Occidental in Ecuador. Average species richness for othersite-series indicated by lines spanning appropriate altitudinalrange; Chamela is westernMexican dry forest.Several of the Andean values are preliminary,being based only on field identificationswith herbarium comparisonof vouchersstill pending or on samples of less than 1,000 m2 (see Table 2).
cializationsfor differentedaphic conditions, incomplete,the trendof decreasingdiversity oftenrelated to differentsoil-nutrient avail- withincreasing altitude is clear. Atleast within abilityin differentAmazonian habitats. the Andes, this inverse correlationis linear (Fig. 10), but the relativelylow diversityof two Central Americanlower montane sites ALTITUDINAL TRENDS suggeststhat the extra-Andeandecrease in Eleven sites in tropical forestsbetween diversitywith altitude may not follow the same 1,500 and 3,100 m altitude,mostly in the rules; certainlyCentral American montane Andes,are includedin Table 2. Althoughthe forestshave very differentfloristic composi- available data set for upland sites is very tionsas well. Althoughthere has been much Volume 75, Number1 Gentry 17 1988 Plant CommunityDiversity
E ~~~~~E O 0%o E ~~E m o E o E 0~ ~~~~~~~ OO ) m'Dt l 0 `1) E 0 IJ OD c %.r. v z 04 0 - 40 = 0o 01 *'E o -~~~ 0~ .s~~~~~~~~~~~~~~~~1 0 C4 0 C" ~~~ 0 E0T 0o 0 0C 0 0 c~~~o~ o E ~ 0 0 ~~~ 0 .0 o ~~~C E~~C E a O C 0 0 0 ~~~ E.E~ E 0 C - 0 0 E E 0 S-C ~~~ ~~ E 0 0 ~~~3~~E 0 0LC ()O Ca z 0cCo 0 0 co 0 o 0o co 0 .2 C ~ 0 co ~ - ' 0 ~~- ca > a. o E C0 0 0) 0 0 0CO >->-0 0 () 0 0 -j > U.W 0
Lowland Mos~ and~ we ~ oetcl hooRgo e Uln oet
Lowland Moist and wet Forests Choc6 Region Wet Upland Forests and Pluvial Forests FIGURE11. Percent of hemiepiphytes(black portion of bar) in sampled climbersfor 0.1-ha samples of upland forests (in altitudinalsequence) compared withlowland Choc6 area and non-Choc6area samples. Note apparent peak in hemiepiphytesat 1,800 m. speculationin the literatureabout a "mid- moststriking is the increasein sampledhemi- altitudebulge" in diversity(Janzen, 1973; epiphytesaround 1,800 m (Fig. 11). How- Janzenet al., 1976; Scott, 1976; Gentry& ever, since increased numbers of hemi- Dodson, 1987b), there is no hintof such a epiphytic species (and individuals) are phenomenonin the data of Figure 10. In- concomitantwith decreased numbers of free- stead, there seems to be a constantrate of climbingliana species and individuals,there decreasingspecies richnessin moistAndean is no net changein communitydiversity. Also forestsfrom the lowlandtropics to near tree noteworthyis therelative abundance of hemi- line. Unfortunately,no sites have been sam- epiphyticclimbers in wet lowlandsites in the pled fromthe Andeanfoothill region between Choco area, a typicalexample of the tendency 600 and 1,500 m, makingit difficultto judge of the forestsof thisregion to have features at what altitudethe decrease in diversitybe- and taxa morecharacteristic of upland forests gins. Clearlythere is no altitudinaleffect up (Fig. 1 1; Gentry,1986b). At higheraltitudes to at least 500 m (Cocha Cashu, Peru; see free-climbinglianas take over again, so that Gentry,1985a). Since samples fromsites at at 2,500 m and above, hemiepiphyteshave 1,700 m wouldbe near the average value for completelydropped out. lowlandwet- and moist-forestsites (Fig. 10), Even near the tree line above 3,000 m, we can assume that there is littleor no de- Andean forestsare more species rich than crease in diversityup to that altitude. are temperateforests. Our highest-altitude Althoughthere is no increase in diversity sample, from3,010 m at Pasochoa in the at middle elevations,there are some note- EcuadorianAndes, has 25 species compared worthyphysiognomic changes. One of the withonly 21-30 species in the richest5% of 18 Annals of the Missouri Botanical Garden
TABLE 4. Representationof differenthabits in local fiorulas (fromGentry & Dodson, 1987b).
Barro Capeira Santa Rosa Jauneche Colorado Habit Number % Number %. Number % Number % Epiphyte(including stranglers) 8 2 19 3 72 12 216 16 Parasites + saprophytes 4 1 6 1 4 1 12 1 Climbers 112 24 115 18 136 22 258 20 Trees - 10 cm dbh 69 15 142 21 112 19 290 22 Terrestrialherbs, shrubs, treelets 270 58 381 58 280 47 540 41 Total species 463 667 604 1,316
a Data fromB. Hammel (pers. comm.). some 312 GreatSmokies Mountains samples is on an unusuallypoor, highlyleached skel- (White,pers. comm.)and 15-26 (X= 20.5) etal soil (Thomas, pers. comm.). forthe 13 othertemperate-zone forests listed West Africanforests, including Nigeria's in Table 1. Omo Forest in my data set and the Ghana forestsstudied by Hall & Swaine(1981), may be poorer in species for historicalreasons DIVERSITY TRENDS SOME INTERCONTINENTAL since there are suggestionsthat most West At a continentallevel, the Neotropicshave Africanforests may have been extensively many more species of plants than do either alteredby Bantu populationsprior to the first the Asian or Australasiantropics (Raven, European colonization(Keay, 1953; Jones, 1976; Prance, 1977; Gentry,1982a). Else- 1956). Even thoughmy anomalouslylow di- where, I have suggestedthat the "excess" versityOmo Forestsite was in a plot of pro- neotropicalspecies are mostlyin herbaceous, tectedforest considered to be climax(though epiphytic,and shrubtaxa thathave speciated surroundedby a mosaic of other plots sub- explosivelyalong the lower slope ofthe Andes jected to varyingdegrees of degradationhis- and in southernCentral America. To what torically)(G. Pilz, pers. comm.),a numberof extent,if any, does highera-diversity of neo- its constituentspecies, such as Pausinystalia tropicalforests contribute to the continental macroceras, Spathodea campanulata, pattern? Markhamia lutea, and Musanga cecro- While I have relativelyfew comparable pioides, seem morecharacteristic of late sec- paleotropicaldata sets, a few generaltrends ondarythan of primaryforest. seem evident.One surprisingindication from Nor is the highdiversity of Central African the available Africandata is thatCentral Af- forestsrestricted to woodyplants. Data com- rican forests(X = 127 spp., N = 5) may be parable to a completelocal florulaare avail- as diversein species ? 2.5 cm dbh as their able forone Africanforest site at Makokou, neotropicalequivalents (X 105 spp., N Gabon (Hladik & Halle, 1973; Florence & 9) forsites with 1,600-2,000 mm of precip- Hladik, 1980; Hladik & Gentry,in prep.). itation.Even thoughthe two high-rainfall sites Comparisonof these data withlocal florulas in Cameroon do not show the increases in fromthe Neotropicsindicates that Makokou speciesrichness that might be expectedin the is not onlyas species rich as equivalentneo- Neotropics,they are still very diverse,and tropicallocal florulas,but it also has a similar the drierGabon samples actuallyhave more habit composition(Table 4; Gentry& Dod- species than would be expected for similar son, 1987b). Similarly,data from 1-ha tree rainfallvalues in the Neotropics.Moreover, plots indicate that Africanforests may be one ofthe highrainfall sites with anomalously almostas rich in tree species as comparable low diversity(Mt. Cameroon)is on the slopes neotropicaland SoutheastAsian forests (Gart- of an active volcano, and the other(Korup) lan et al., 1986; Thomas, pers. comm.: 138 Volume 75, Number1 Gentry 19 1988 Plant CommunityDiversity
TABLE 4. Continued. protectedby being an island (Raven & Ax- elrod, 1974; Axelrod& Raven, 1978). Rio Palenque La Selva- Makokou Quite the oppositeof Africa,Asian forests have been widelythought to have more tree Number % Number % Number % species thanneotropical forests (e.g., Ashton, 238 23 368 25 66+ 6+ 1977; Whitmore,1984). This conclusionwas 6 1 8 1 9 1 based on comparisonof extant neotropical 171 16 182 12 259 23 165 16 310 21 389 34 data for 1-ha tree plots with similarAsian 475 45 622 42 418 37 data sets. However,the previouslyavailable 1,055 1,490 1,140 neotropicaltree plots were all fromareas that would be anticipatedon biogeographicalor ecological groundsto have species-poorfor- spp. in 0.64 ha on transect S, Korup National ests (Gentry,1988). Hectare plots in upper Park, Cameroon; Gentry, in press). Amazoniaconsistently have moretree species On the other hand, it is noteworthy that than in most Asian forests(Gentry, 1988), my single Madagascar site is richer in species and the most species-rich1-ha plots are in than any of the continentalAfrican sites, which upper Amazonia. Indeed, these plots are so might be anticipated from the now widely diverse-up to 300 species out of 606 in- accepted hypothesis that Africa's low conti- dividuals - 10 cm diameterat Yanamono, nent-wide plant (and bird) species richness Peru-that it is hard to imaginehow a forest stems largely fromextinctions associated with could be much more diverse. climatic deterioration during the Pleistocene I concludethat plant community diversity, or late Tertiary, whereas Madagascar was at least of woodyplants in plots of 1 ha or
15~~~~~~~~~~~~~~~~~~~~~~~~~~~~~C 0~~~~~~~~~~~~~~~~~~~ x ~ ~~ ~ ~~~~~~~20 0 ~~~~~~~~~~~~~~z o X C
E
> Q 0 z - EL~ .0 C
0 .0~~~~~~~0 0 0 .Z 0
FIcSURE I1-2. Basal areas for 1 ha saiples of forest types. 0 some different Lige-average leasa area foresttype;, bar-= 1 d-. fr B sa 20 Annals of the Missouri Botanical Garden
% of species
10 20 30 40 50 60 70 so 90 100 Yanamono ao | > | X | > | C | X |, | (D | a0 = | > 1( 46 other families Tambopataupl. 1 | ? | |oI| -.I 2[= 1? rmIKKI^' 30 otherfamilies
Tambopata upl. 2 r | t Z > | > ] co I t | m I mDI | | | | C 34 other families ~~~~ I I~~~~~~~~~~~~~~~~~IM Tambopata alluv. r I 0 | , | | | | 31 other families
Cocha Cashu r. o '|X|@|m|r|<|P 0 37 other families Tambopata~~~~~~~~~~~.p.
Cabeza de Mono co I o mI' m ni- oI5]oID |=|> mI 28 otherfamilies (a~~~~~~~~~~~~~~~~~~~~ InmiIieI Mishana r >c | > | ' | , | ? | ' | < |- | = | < | v | 31 other families D . ?|t|<| D|?)|D12te aiis Koroaalup. rO O
Neblina r m t. | | | | D) | -> | > | 21f other families I I ~ ~ ~ ~~~~ci,'~~~MI
CD Anulha.u | 0 | | WI other families
(pers. comm.);(200Makokou are)the the total for the- 10 cm (db s e f 280.1-a potsliest in
plotsae dep Monoas o r (D n Fml 0 cili 3e oerfamiies KuaelaBaongtaeaeKornmonto Xig) mel eta= Meliaceae,fia (KrpadMkku)nsap = Sapotaceae (thepresent,=Sapindaceae),myrI= second,otes if Asi (Kal Beaog fAmiules. = Melastomataceae,mel = Meliaceae, sap = Sapotca (h second i prset = Sapndcee) mr Myristiaceae, yt Mytaceae.Note tht Legumnosae, he domiant fa Iy in lll2eotopical' fandAficans Myristicandae,myt = Myrtaceae.Note that Leguminos, 4 otherfamilies
the foests o all hreecntinets aremostlycompoed of pecie beloning t th sameDfew w1oodyfamilies.
(Yanamonotijuto Xinu) CpentrsealAfica (Kteocrupandeakoinou)anSotheastAsia.lont (KualaBxelalfong Andulao).ps pleforstse p al otherwe nontinedFarmly codeoaet ofirtpetters belof thet familiaeexsmfew t
less,has a similarrange of variation according Perinet),and a few otherislands (e.g., New to local environmentalconditions in all three Caledonia: 20 palms - 10 cm dbh/ha at of the world's main tropical regions; what Riviere des Pirogues). While stem densities happens at larger spatial scales remainsan of trees - 10 cm dbh may be similarfrom open question. continentto continent(Dawkins, 1959), trop- Althoughtropical foresta-diversity may ical Africanforests tend to have more large be similaron differentcontinents, its structure treesand higherbasal areas (and presumably is not. For example,lowland neotropical for- biomasses) (70.7 m2/ha vs. 34.9 m2/ha) than ests have fewerlianas than Africanforests do neotropicalor Australasianforests (Fig. and morelianas than Asian forests(Emmons 12). On the other hand, Asian dipterocarp & Gentry,1983). Large palms as a major forestsmay have uniquelyhigh densitiesof and characteristiccanopy element of lowland small polelike trees. Such structuraldiffer- terra firmeforest seem largelyrestricted to ences, onlybeginning to be discovered,may the Neotropics(Gentry & Emmons, 1987), be criticalto forestorganisms. For example, Madagascar (20 palms - 10 cm dbh/ha at theintercontinental difference in liana density Volume 75, Number1 Gentry 21 1988 Plant CommunityDiversity
AV. FOR 20 LOWLANDNEOTROPICAL MOIST AND WET SITES
c I o ] B z g ^ | O | S| | | |i~in |E Q~i| g53|R~~ta~vfor89 fams. with-2 8PP.av 5? | AV. FOR 4 SITES ON WHITESANDS zZ Ps ;t t S F 0 F | S 8 t Q { 1 r ^ iS O r Av. for42 fams.with'2spp.av. 3; z
>| || OF 35 fams. with AV. FOR 2 LOWLANDPLUVIAL SITES 1 ||:|l -e2sppa 4 |gc||| |r ~P for Ac ]5 Ioo ' | o 2 tt |et i i |w| !|2| l |n||; Ac. 38 fams- with AV. FOR AFRICA (5 SITES W/O OMO)
rl~ ~ ~ ~~ ~ ~~~~~~~~~~~~Vo r1 E|?I J, I z]Dl>| ,lB|gt?IaIH ~o110 UI- Avi for 27 fams. with AV. OF 2 BORNEO SITES J I <2 spp. av.I
c[ | l 3 |g | | Wl > 1H g|> 1?X|SF1>l Sc 21fams. with1 spp.DAVIES RIVER ST. PK., AUSTRALIA F S F RIVIERDESPIROGUES, | *, o | ,l FS| | 4F | > { ? |W T ? ? | | v || |s FS~ 16 fams. with NEWCALEDONIA ha 1 55 5 lapieah FIGURE 14. Comparisonof average numberof species per familyfor 0.1-ha samplesfrom subsets of different lowland neotropicalforest types with equivalentpaleotropical data. From top to bottomthe columnsrepresent: 1) average for 20 lowland neotropicalmoist and wet sites; 2) average for 4 neotropicalsites on whitesand; 3) average for 2 pluvial-forestsites in Choc6; 4) continuationof 3; 5) average for 5 centralAfrican sites (i.e., excluding Omo); 6) average for 2 Bornean sites; 7) continuationof 6; 8) Davies River State Park, Queensland, Australia; 9) Riviere des Pirogues, New Caledonia. Shortestcolumn segments are two species tall. may have been the -criticalfactor selecting rica, on the richvolcanic soil ofthe Mt. Cam- for differentlocomotor adaptations among eroon plot, several families, especially canopy vertebrateson the three continents Rubiaceae,Apocynaceae, and Euphorbiaceae (Emmons & Gentry,1983). have morespecies thanlegumes, but thisfor- est, on the lowerslopes of an active volcano, may not be strictlyprimary. FLORISTICS The otherfamilies that contribute most to Neotropicalplant communities are put to- species richnessof differentplant communi- getherin decidedlynonrandom ways. Thus ties are also predictable.In the Neotropics community-levelfrequency of differentseed the same 11 families Leguminosae, Lau- dispersaland pollinationsyndromes is gen- raceae, Annonaceae, Rubiaceae, Moraceae, erallypredictable from environmental param- Myristicaceae,Sapotaceae, Meliaceae, Pal- eters (Gentry,1982b, 1983). Similarly,the mae, Euphorbiaceae, and Bignoniaceae- floristiccomposition of differentplant com- contributeabout half(38%-73%; X = 52%) munitiesis remarkablyconsistent, at least at of the species richnessto 0.1-ha samples of the familiallevel. Legumes are virtuallyal- any lowland forest.At least eight of these ways the dominantfamily in neotropicaland families are always among the ten most Africanlowland primaryforests. The only species-richfamilies in any lowlandneotrop- neotropicalexceptions are on extremelyrich ical moist or wet forest(Fig. 14; Gentry, soils where Moraceae become very diverse 1987b). Similarly,in 0.1-ha samples of low- and are occasionallyas species-richas Le- land neotropicaldry forests,Bignoniaceae, guminosaein 0.1-ha plots (Gentry,1986b, the preeminentliana family,is alwayssecond c). Of the 43 continentalneotropical lowland only to Leguminosae in its contributionto 0.1-ha samples between 23.50N and S lati- species richness(Fig. 15). tudes, 39 had Leguminosae as the most Somewhatsurprisingly, the dominantfam- species-richfamily. The dominance of le- ilies in neotropicalforests also tend to be the gumesin the Neotropicsand Africais equally mostspeciose on othercontinents. Rubiaceae, apparentwhen only trees - 10 cm dbh are Annonaceae,and Euphorbiaceae are always considered(Fig. 13). Indeed, legumes con- among the ten most species-richfamilies in tributealmost exactly as muchto thediversity Africaand Asia, just as theyare in the Neo- of neotropicaland Africanforests as dipter- tropics.The rest of the 11 mostspecies-rich ocarps do in SoutheastAsia. Similarly,in Af- neotropicalfamilies (Lauraceae, Moraceae, 22 Annalsof the MissouriBotanical Garden
~~ 1~~~~I o14other Capeiral c I I | | I- families
Boca de Uchire| I| c I I ; h .InI WHlI Rt
Llanosi I| | c | |I families t 0m)
I Blohm Ranch I | >' 1 1 20 other families
Tayrona| I| | I| I 20 other families
Guanacaste(upQ c I w I W 14 other 1
Guanacaste(gal)I r | I cI > | II o In kki|13 mother .
Tarapoto E 0
FIGURE 15. Numberof species per familyfor 0.1-ha samples of lowland neotropicaldry forests. For three sites withsample areas of < 1,000 m2-Llanos, Guanacaste (upland) and Guanacaste (gallery), with500 n2, 700 i2, and 800 m2 of sample area, respectively-the actual values are inside the solid outlines with the anticipated number.of species in 1,000 m2 indicated by the dotted outline. Shortestcolumn segments are two species tall.
Sapotaceae, Palmae, Myristicaceae, Meli- are only occasionallyrepresented by one or aceae, and Bignoniaceae)are all represented two species in the Neotropicsand are absent in at least some samplesfrom both Africa and frommy Asian samples. Apocynaceae and Asia and, except for Bignoniaceaeand Pal- Sapindaceae almostalways turn up in samples mae, are among the ten most species-rich fromany continentbut are generallyamong familiesin at least one Africanor Asian sam- the ten most species-richfamilies in Africa ple. Thus, withthe exceptionof the substi- (alwaysin the case of Apocynaceae)but only tutionof Dipterocarpaceaefor Leguminosae rarely elsewhere. Disproportionatelyrepre- as the most species-richwoody familyin sentedin Asia, besidesDipterocarpaceae, are SoutheastAsian forests,pantropical familial Myrtaceae (always among the most species- compositionof lowlandforests is remarkably rich familiesvs. almost always presentbut similar. onlyrarely among the mostspecies-rich fam- Otherminor differences include Ebenaceae ilies in the Neotropicsand representedby a (almostalways present in Africaand Asia and singlespecies in a singlesample on continental among the ten most species-richfamilies in Africa).Other noteworthy anomalies include about halfthe samplesfrom those continents 9 speciesof Proteaceae, 7 ofElaeocarpaceae, but onlyoccasionally represented in the neo- and 6 ofMonimiaceae in theQueensland sam- tropicalsamples, never by morethan a single ple (thesethree families ranking 3rd, 5th, and species), Olacaceae (usually representedon 6th in diversityafter Lauraceae, Myrtaceae, all continentsbut generallyamong the ten and Rubiaceae), 7 Araliaceae species and 5 mostspecies-rich families in Africa,never so of Cunoniaceaein the New Caledonia sample in Asia or the Neotropics),and Sterculiaceae (ranking5th and 8th,respectively, in familial (alwaysamong the ten mostspecies-rich fam- diversity),and 8 and 3 species, respectively, ilies in Africa;represented by 1-3 species in of Xanthophyllum(Polygalaceae) at Semen- almostall neotropicaland Asian samples,al- goh and Bako, Borneo. thoughamong the ten mostspecies-rich fam- Put anotherway, all of the paleotropical ilies onlyin Cocha Cashu, Peru). Dichapeta- forestssampled were constitutedalmost en- laceae are almostalways among the ten most tirelyof the same plantfamilies encountered species-richfamilies in Africansamples but in equivalentsamples of neotropicalforests. Volume 75, Number1 Gentry 23 1988 Plant CommunityDiversity
Although13 familiesnot representedin the An average of 30% (withextremes of 25% Neotropicswere included in the paleotropical at Korup to 34% at Belinga) of the genera samples,and althougheach Africanand Asian at the six continentalAfrican sites are neo- sampleincluded 1-3 familiesnot represented tropicalgenera, nearly all also includedin the in the Neotropics,with two exceptions,the neotropicalsamples. When completelocal flo- sum contributionof all of these to species ras are compared,generic concordancebe- richnessof the Asian and Africanforests is tweentropical Africa and the Neotropicsre- negligible.The two exceptionsare Diptero- mainsequally high. Thus 30% of the genera carpaceae in tropicalAsia and Pandanaceae representedat Makokou Gabon also occur in in Madagascar (3 spp.), Queensland(2 spp.), the Neotropics.Both sets of figureswould be and New Caledonia (4 spp.). Excludingthese much higherif such tenuouslydifferentiated twofamilies, an average of 2 species (and ca. genera as Pycnanthus and Virola (Myristi- 3 individuals)per sample was contributedto caceae) or Macrolobium and its segregates paleotropicalcommunity diversity by families (Leguminosae)were consideredto be conge- not included in the equivalent neotropical neric. samples.At thislevel New Caledonia was the Genericoverlap between tropical Asia and mostdistinctive, with one specieseach of Bal- the Neotropicsis less, averaging23%, and anopaceae, Epacridaceae, Oncothecaceae, betweenAustralasia and the Neotropicsin- and Pittosporaceae,plus 4 of Pandanaceae. termediate(25% neotropicalgenera in the The Madagascar sample included,besides 3 Queensland sample, 26% in the New Cale- Pandanaceae,a speciesof Sarcolaenaceae and donia one). These relationshipsmight be pre- twoof Pittosporaceae, the Queensland sample dictablefrom Cretaceous and Tertiaryplate a species of Balanopaceae and 2 of Pandana- tectonichistory and the timetableof Gondwa- ceae (plus one of the sometimesCunoniaceae nan breakup. In this light,it is especially segregateDavidsoniaceae). In Africa,Ancis- interestingthat about 36% ofthe genera sam- trocladaceaewas representedby one individ- pled at Perinet,Madagascar, are sharedwith ual at one site, Medusandraceae by one in- the Neotropics,the highestvalue forany pa- dividualat one site, and Scytopetalaceaeby leotropicalsite. twospecies at one site. Onlyin the lattercase There are also consistentand predictable did an endemicfamily contribute significantly floristicchanges along environmentalgra- to a site's diversity,with Ouabangia alata dients,at least in the Neotropics.On poorer the 5th mostcommon species (13 individuals) soilsfamilies like Burseraceae, Lauraceae, and at Korup and Rhaptopetalumcf. coriaceum Sapotaceae become more prevalent,whereas representedby threeindividuals at the same on the richestsoils palms and Moraceae are site. It is perhaps worthnoting that several disproportionatelyspeciose. of the endemicfamilies included in the above In neotropicalareas witha strongdry sea- totalare somewhatdubious segregates-Pan- son, floristiccomposition is likewisepredict- daceae (from Euphorbiaceae), Irvingiaceae able. Leguminosae are always the most (from Simaroubaceae), and Ixonanthaceae species-richfamily, with Bignoniaceae, rep- (from Linaceae). Lowland tropical forests resentedmostly by wind-dispersedlianas, al- throughoutthe world are overwhelmingly ways second (Fig. 15). made up of the same plantfamilies, with the On an altitudinalgradient in the Andes, exception of the Dipterocarpaceae for Le- Lauraceae consistentlyreplace Leguminosae guminosaesubstitution in SoutheastAsia. as themost species-rich family at intermediate Even at thegeneric level, there are striking elevations(Fig. 16). Otherfamilies that con- floristicsimilarities between the compositions tributeto the diversityof middle elevation of lowlandtropical forests on differentcon- forestsare Rubiaceae, Melastomataceae,Eu- tinents.The generic similarityis especially phorbiaceae,Moraceae, Guttiferae, tree ferns, markedbetween Africa and South America. (hemiepiphytic)Araceae, and Palmae. Fam- 24 Annals of the Missouri Botanical Garden
CO ilies like Bignoniaceae,Sapotaceae, Myristi- caceae, Meliaceae, Sapindaceae, Bursera- w > ceae, and Chrysobalanaceaeare especially noteworthyas absent or much more poorly
LCJV 2 representedthan in lowlandforests. At higher elevations(> 2,000 m), Melastomataceae,
o Compositae,Rubiaceae, and tree fernsbe- come more prevalent,although of these only ERIC U C o V Compositaeincrease in absolute numberof species. At even higheraltitudes, Aquifolia- MY I L ceae, Myrtaceae,and Theaceae become rel-
OFCHR _C02 ativelymore important, while near timberline CC Compositaeand Ericaceae predominate. IIYRT04 2 E O Curiously,the site at 1,000 m altitudeat 0~~~~ > 0~~~~ 0O Perinet,Madagascar, had virtuallyan iden- CC J tical familial compositionto the middle- 111111P ARAC C elevationneotropical site; in additionto Lau- SAco _O V raceae being the most speciose family, < 0 Rubiaceae, Euphorbiaceae, Moraceae, and GUTTGUUTT > r Guttiferaefollowed in species richness;the FLAF CYCLW onlysubstantial differences are a transposition ofthe roles of Melastomataceae (more species
MYRT 0 in the Andes) and Myrtaceae (more species at Perinet),the presence of several species ofMonimiaceae and Oleaceae in Madagascar, CO and the frequencyof hemiepiphyticAraceae in the Neotropics(Fig. 17). A Queensland, EUP11 FER14~~~~~~~1 Australia,site from850 m was also rather PAL11 ET 0g similarin familialcomposition to the Andean
K , b 00m50osaper middle-elevationsites, again withLauraceae MORRA 2u neoropca mos- an e-oetsmpe;2vrg dominating,closely followedby Rubiaceae, RUB NT ~ thoughwith greater prevalence of such south-
FIGURE F6NmerN ofspce e aiyfr01 ern familiesas Proteaceae, Elaeocarpaceae, ALM and Myrtaceae.Such strikinglyrepeated pat-
LELU MEL AQT D ternsin partsof the world so widelyseparated BIGN >~~~~~~~~I today can hardlybe due to chance.
MORA 0LA LAUE Many of the major latitudinalchanges in floristiccomposition are wellknown, with fam- FIGURE16. NumberofQUI spce e famlycor01 Lehe URrg .roKney C ic ugr) ) Cer ilies such as Fagaceae and Juglandaceaere- left to rightcoumns are 1) aveag fo 0loln neotropicalmist- and wetfores sapls;2 aerg placing the tropicaltaxa in North America for sitsRbewee 1,0-2,00m(CroEihao Incahuar, Venceemos, FrralnsBeCl);3Iv (Fig. 18). Perhaps less emphasizedare how remarkablysimilar in familialcomposition dif- ferenteastern North Americanforests are. Kennedy,ColombiaU(,0R m 0 mUofsapl are) While species,and to some extentgenera, do change fromplace to place, froma world
5) Pasochoa, Ecuador (3,010 m, 200 m2 of sample area). Site datafromTable 2. Shortestcolumn segments are two species tall. Volume 75, Number1 Gentry 25 1988 Plant CommunityDiversity
I I ~~~~~~~~~~'II"dI ~r8fas.wt I | I SoI~ EI r |IS Av. for 62 fams. with<2 spp. av. | AV. FOR 4 NEOTROPICAL SITES 1000-2000 m. FIGURE 17. Numberof speciesper family for 0.1-ha sampleat Perinet,Madagascar (950 m) (top two columns)compared with average for four mid-elevation neotropical sites (1,000-2,000 m) (bottomtwo columns). Notethe remarkable similarity offamilial composition. Perinet data basedonly on field identifications pending herbariumcomparison of vouchers. Shortest column segments are twospecies tall. perspectivethe overall floristiccomposition position are highly predictable from of mostof these forests is as similaras is their environmentaland geographicalfactors, with diversity.The contrastinglyaustral compo- maximumplant communitydiversity occur- sitionof the Valdivian flora is also wellknown. ringin full-tropicallowland areas withrich to There are also floristicsimilarities between intermediatelyinfertile soils and high annual the austral and northtemperate ones. For precipitationand/or littledry-season stress. example, gymnospermsand Fagaceae be- Such patternsare oftentaken as evidenceof come moreprevalent in bothnorth temperate niche saturationand communityequilibrium and south temperateareas. One interesting (MacArthur,1965, 1969; Cody, 1975; see and previouslyunremarked floristic difference also Whittaker,1977). betweenthe Valdivianforests and theirnorth- Much ofthe controversyabout equilibrium ern equivalentsis that the formerlack sym- vs. nonequilibriumcommunities has focused patriccongeners. The differencein diversity on the role of niche specificityvs. stochastic betweeneastern North American and Valdi- generationor maintenanceof diversity(e.g., vian forests(as well as between the North Hubbell, 1984; Hubbell & Foster, 1986; Americanforests and mytwo Europeansam- Ashton,1969; Connell,1978). My data sug- ples) is almostentirely accounted for by this gestthat even thoughtropical forests contain lack of sympatricspecies in generalike Quer- many differentplant species, they are far cus and Carya. Why Chilean Nothofagus fromrandom assemblages. Can thesedata and species,unlike their northern cousins, should conclusionsbe reconciledwith the very dif- be almost entirelyallopatric is unclear, but ferentones of Hubbell (1979; Hubbell & the effectof this patternon the diversityof Foster, 1986, 1987)? Below I willfocus on the southtemperate forests is obvious. several pointsthat may be relevantto this debate. From a somewhatdifferent perspective, DISCUSSION some authors(e.g., Federov, 1966) have ar- To thispoint I have attemptedto present gued that the exceedinglyhigh diversityof a seriesof observations of changes in diversity tropicalforests is too great to be accounted and floristiccomposition on variousgradients. forby niche specificity;therefore, some kind I now focusbriefly on some theoreticalgen- ofnonselective or stochasticmechanism must eralizationsthat would seem to derive from be invoked.However, it seems to me that it these data. is stochasticallymost unlikelythat the ex- The overall message is that plant com- tremespecies richnessof forestslike that at munitiesare put togetherin decidedlynon- Yanamono, Peru, with 300 species out of random ways. Diversityand floristiccom- 606 individualsin a hectare, would result 26 Annals of the Missouri Botanical Garden fromrandom processes, unless there is a po- tentialsample universe of manythousands of tree species. Forty-eightspecies are repre- sentedin the first50 individualssampled at 0 Yanamono,and the 65 individualsin the first I.:2 Yanamono 0.1-ha subplot constitute 58 z0) species.Such highlevels of diversity, far from o o indicatingstochasticity, would seem to indi- 0 0 cate verystrong ecological pressures resulting N x o s in phenomenallylow densities of the individual < a, species (and highcommunity diversity). The strikingregularities in the patterns MALP 1 GUTI O 0 discussedabove clearlyindicate that at some LECY levels both communitycomposition and di- MYRT versityare highlypredictable. How this re- FLAC CHRY lates to community equilibrium remains BURS clouded,however, in part because of defini- APOC VIOL tional problems. Hubbell & Foster (1986) SAPI VERB definedan equilibriumcommunity as one in TILT POLY which a particularcombination of species MELI HIPP FLAC maintainsitself against outside perturbations, IYRII CELA whereasthe predictable diversities of different ANNU EUPH URTI tropicalforests with similar environments but SAPS differentassemblages of species is more akin PALT SOLA to the "equilibrium"theory of island bio- MYRT geography(MacArthur & Wilson, 1967), SAPO COMP . co consideredby Hubbell as a nonequilibrium RUBI ARAC . U) theorybecause of the taxonomicrandomness RUBI 0 involved.Many Amazonianforests are clearly LAUR SAPT O richerin tree species than equivalentCentral W Americanforests (Gentry, 1988). They also PIPE - ~ ~ have muchgreater habitat differentiation and PALF co0 3-diversity(Gentry, 1986a). Thus some of the higherdiversity of the Amazonianforests (wtfret8 N 00m a E r l 4 - 0 a maybe due to the "mass effect"phenomenon of Shmida & Wilson (1985), withaccidental AMUR R jj immigrantsadapted to other environments ANN contributingsignificantly to the a-diversityof BIGN PTJSRES colunRA :1 vraefr2 oln netoial an individualAmazonian forest. Arguing along LESS LEGS MEET LGS FG FG mois- ad wt-fres saple;) Lo Tutas, 0eic similarlines fromthe nonequilibriumview- MOala 4gnia(rfoet 24?0S ,30m;5 L4gniAU (mis foet LIGa44', 1,0 SBAS l.;4 MEE point, Hubbell & Foster (1986) suggested (28?15'-3 9?2 '); 6)Sd erakteoGemn that biogeographicalpattern plays a major FIGURE 18. Numberof species per familyfor some role in tropicalforest a-diversity: if the re- 1-ha at 0. samples differentlatitudes. From lelft' to right, gional diversityis greater, as it certainly is in columns are: 1) average for 20 lowland neotropical moist-and wet-forestsamples; 2) Los Tuxtlas,Mexico Amazonia, more species, on the average, (wetforest, 18035'N, 200 m alt.); 3) Parque El Rey, Argentina(moist forest, 24045'S, 1,000 m alt.); 4) Salta, Argentina (dry forest,24040'S, 1,300 in); 5) average for seven temperate North American sites (54"N); 7) average for three Valdivian, Chile, sites (28015 'N-3902 'N); 6) Suderhackstedt, Germany (39?30'S-40043'S). Volume 75, Number1 Gentry 27 1988 Plant CommunityDiversity shouldoccur in individualforests due purely subcanopytree Leonia glycicarpa, whichhas to phenomenaassociated with patch dynamics 6-19 individualsper hectare,and the canopy and local immigrations.But there are also tree Symphonia globuliferawith 1-4 indi- problemswith such interpretations.That the vidualsper hectare,again excludingthe sec- familiesand genera representedin these dif- ond growthplot. ferentsamples are so predictablestrongly sug- At the oppositeextreme are the 21 habitat gests that at least some kind of familial-spe- specialistslisted in Table 5, locallycommon, cificniches may be involved.Moreover, the but occurringin only a single habitat:good apparentpartitioning of the species of each soil,poor soil,swamp, or second growth.The familyinto different sets of speciesspecialized extremecase is Lueheopsis hoehnei,the ab- for differentsubstrates in Amazonia seems solutedominant in the swamp plot with265 strongcircumstantial support for selectionist trees,but completelyabsent elsewhere;that interpretations(Gentry, 1985b). thisis onlythe secondrecord of such a locally Data fromseveral 1-ha tree plots in the commonspecies fromPeru is instructiveas Tambopata Reserve, Madre de Dios, Peru, to the state of AmazonianPeruvian floristic can be used to documentthe effectof sub- knowledge.Another example worth mention- stratespecificity on speciescomposition. Data ing is Sparrea schippii, previouslyunre- are available fromtwo completelyidentified portedfrom Peru (or indeedfrom Amazonia), 1-hasamples from similar poor-soil terra firme whichis the fourthmost commonspecies in forestseparated by about 1.5 km, a com- the alluvialplot. The large numberof species pletelyidentified plot in matureforest on rich thatare completelyfaithful to a singlehabitat alluvial soil, and from as yet incompletely (presumablyalso includingmany additional identifiedplots in youngriverside secondary less commonspecies not listedin Table 5) is forest,in swamp forest,and in forestin a a good example of the importanceof niche transitionalarea betweenthe rich floodplain specificityin maintainingoverall Amazonian and poor-soiluplands (see Fig. 8). As is usually species diversity.Each communityis rich in the case in species-richtropical forests, most largepart because ithas manyspecies unique- of the species sampled were representedby ly adapted to a specificsubstrate. one or two individualson a single plot and Perhaps more interestingfrom the view- are inadequatelysampled to draw any con- pointof ecological theoryare the othertwo clusionsabout habitat specificity. Table 5 lists distributionalcategories indicated in Table 5. the species thatoccur in all threecompletely The firstare species thatare commonin one sampledplots plus all speciesthat are common habitatbut also have a fewindividuals in one (i.e., > 10 individuals)in at least one of the or more of the otherhabitats. Some of these plotsplus a fewother selected species. mayrepresent cases of"mass effect"(Shmida At one extremeare 13 species that occur v& Wilson, 1985), withan occasionalindivid- both in the two poor-soilplots and in the ual survivingbut not reproducingoutside its fertile-soilalluvial plot. These mightbe classed normalecological range. The second pattern as ecologicallyinsensitive; none of them oc- is species of the poor soil forestthat are com- cursin the secondaryforest, six of them(and monin one ofthe twosample plots but absent possiblymore) in the swamp plot, and most fromthe other. These may be examples of (perhapsall) ofthem on theintermediate plot. "ecological equivalents"(Shmida & Wilson, Allof these are essentiallyuniformly dispersed 1985), where due to some accident of dis- withsimilar numbers of individualsin each persalor establishment,a given species occurs hectare.Bertholettia excelsa, whichhas 1- at one site but not at anotherwhere it would 2 large emergenttrees per hectare through- be equallywell adapted. The ecologicalequiv- out the Tambopata Reserve (except in sec- alenthypothesis seems especiallygermane to ondaryforest), is a good exampleof thispat- Cordia, whereCordia mexiana and C. pan- tern. Other good examples include the amensis occur in one upland plot while C. 28 Annals of the Missouri Botanical Garden TABLE 5. Differencesin occurrenceand abundance in different1-ha treeplots of some commonTambopata species (all species occurringin all threecomplete plots or with 10 or more individualsin any one plot plus a few others). Plot 1 is relativelyfertile terra firme; plot 2 is swamp forest;plots 3 and 6 are on poor sandy, upland terrafirme; plot 4 is on rich alluvial soil; and plot 5 is in young riversidesecondary forest. Plot Number 1 2 3 4 5 6 Ecologicallyinsensitive, ? uniformlydispersed Bertholettiaexcelsa 2 (1) 2 1 - 2 Eschweilera coriacea 6? ? 4 2 - 9 Glycidendronamazonica 1 (1) 1 2 - 1 Leonia glycicarpa 19 (1) 12 12 - 6 Lindackeria paludosa 4 (1) 10 1 - 4 Minquartia guianensis 1 - 3 1 - 2 Nectandra cissiflora ? ? 1 1 - 4 Neea divaricata X ? 2 5 - 4 Ocotea rubrinervis ? ? 7 7 - 7 Oenocarpus mapora 1 (1) 4 3 (4) - 3 Symphoniaglobulifera 1 (3) 3 3 - 4 Tapirira guianensis 1 - - 1 - 2 Clarisia racemosa 1 3 2 - 2 Ecologicallysensitive but widespread Amaioua corymbosa 1 (1?) 11 1 _ 6 Euterpe precatoria 17 4 2 2 - 4 Iriartea deltoides 106 (15) 7 86 - - Iryantherajuruensis 5 (3) 19 5 - 22 Iryantheralaevis 17 (2) 13 2 - 31 Mabea - (1) 1? 11 - - Pourouma minor 18 (6) 17 1 - 44 Pseudolmedia laevis 14 (5) 4 7 - 1 Siparuna decipiens 13 3 8 1 - 9 Socratea exorrhiza 10 5 1 38 7+ 2 Tetragastrisaltissima 1 (2+) 7 1 - 22 Ecologicallyrestricted Cecropia membranacea - - - - 46+ Ficus insipida - - - 13 Citharexylumpoeppigii - - - - 9+ Sparrea schippii - - - 17 Rinorea viridifolia X - - 27 Astrocaryummurumuru - - 16 Myroxylonbalsamum 1 ? - 6 - - Cordia lomatoloba - 2- Cordia nodosa X - - 1 Mauritia flexuosa - 1 - - - - Lueheopsis hoehnei - 265 - - - - Pithecellobiumlatifolium - 12 - -1 Rouchera punctata 1 (2) 19 - 15 Virola sebifera 1 (1) 18 - 15 Ouratea - 14 - - 14 Euceraea nitida - (1) 6 - _ 8 Cedrelinga cateniformis - - 3 - - 5 Cordia mexiana - - 10 - - - Cordia panamensis - ? 4 Cordia toqueve - ? - - - 4 Cordia ucayaliensis - - - - - 7 Volume 75, Number1 Gentry 29 1988 Plant CommunityDiversity TABLE 5. Continued. Plot Number 1 2 3 4 5 6 Major densitydifferences not explainableby ecology Bixa arborea - 15 - Hevea guianensis 1 15 - Pseudolmedia laevigata 1 23 - - 4 Ocotea (domatia) ? 1 - - 10 Arrabidaea tuberculata - - - - - 4 X = presentin Hartshornplot but numberof individualsnot known. ? = presenceor absence not knowndue to incompleteidentifications (plot 1) or samplingnot yet completed (plot 2). ()= species occurringin plot 2 onlyin corneron higherground. toqueve and C. ucayaliensis occur in the generallynot abundantat differentsites with other.Both of the lattersituations represent similarecology, they are usuallypresent. If the patternthought to be prevalenton Barro we take the three rich-soiltree plots as an Colorado Island (Hubbell & Foster, 1986), example, all the abundantTambopata allu- withhigh diversity of a givencommunity due vial-plotspecies are presentin the Yanamono in large partto nonequilibriumfluctuations in plot,and all the abundantYanamono species, its species. except Otoba glycicarpa and Carapa gui- At a differentlevel, my data on plantcom- anensis, are presentat Tambopata.All of the munitycomposition also seem muchless pre- abundantCocha Cashu species are at Yana- dictableand much more in accordance with mono,and all but fourof the abundantYana- the nondeterministic,nonequilibrium view- monospecies are at Cocha Cashu. If we com- point. In the nine 1-ha tree plots that have pare the sandy-soilplots fromMishana and been analyzed,there was not a singlerepe- Cabeza de Mono, there is only one species titionof a most-dominantspecies. Although abundantat both sites (Hevea guianensis), one (or a few) species is always much more but all the commonCabeza de Mono species common, there is a different"dominant" are presentat Mishana,and mostof the com- speciesin each plot.Even ifthe severalmost- monMishana species are at Cabeza de Mono. dominantspecies in each plot are compared, In contrast,only four species that are abun- thereis littleoverlap. Considering only those dant at any poor-soilsite are presentat all species with10 or moreindividuals per hect- in any rich-soilsite, all at Yanamono, which are in at least one tree plot generatesa list has an intermediatelevel of soil fertility.The of 54 species documentedto be relatively relevantpoint is that althoughthe species commonlocally somewherein upper Ama- presentat a site may be predictable,the fre- zonia. But ofthese, only five species are abun- quency of a particularspecies in different dant on twodifferent plots. The sharedabun- forestsseems entirelyunpredictable and is dantspecies include Astrocaryum murumura, likelydetermined stochastically. This is sim- common on all three rich-soilplots (Yana- ilar to the concept that Shmida & Wilson mono,Cocha Cashu,Tambopata alluvial), and (1985) have termed "ecological equivalen- Hevea guianensis, commonon three poor- cy," i.e., the coexistenceof species withef- soil plots.The othershared abundant species fectivelyidentical niche and habitatrequire- are Otoba parvifioraon twoof the three rich- mentsfor largely stochastic reasons. It is also soil sites (Yanamono and Cocha Cashu) and the patternthat would be predictedby Hub- Iriartea deltoidea on a differentpair of rich- bell's (1979; Hubbell & Foster, 1986) com- soil sites (Cocha Cashu and Tambopata al- munitydrift theory. Indeed, Grubb (1986) luvial).But even thoughthe same species are generalizedthat the relativelysparse or rare 30 Annals of the Missouri Botanical Garden species that of necessity constitute the bulk plantcommunity that a biogeographermight of the species of species-rich communities define.The numerousmicrohabitat specialists should interact so infrequentlywith each oth- suggestedby a casual glance at a series of er that niche differentiationbecomes largely the Hubbell-FosterBarro Colorado Island dis- irrelevant. tributionmaps become nonspecialistsif the The same conclusion arises from the 0.1- relativelyfew individuals that occur away from ha samples. There are almost always a few a favoredhabitat are emphasized.I suspect very common species in any sample. One of thatdifferences in taxonomicfocus may also these is usually much more common than all relateto theinterpretational differences. Hub- the others; at 11 sites the most common bell focusedentirely on a particularcombi- species was between two and seven times more nationof species in addressingthe question common than the second most common of communityequilibrium. My data suggest species. Yet the only repeat of a "most dom- thatwhile the species thatmake up different inant" species among 25 moist- and wet-for- communitiesmay be very inconstantfrom est sites is Catoblastus velutinus, shared be- place to place, at the same timethe different tween Rio Palenque and immediatelyadjacent families(and perhapsgenera) that contribute Centinela in western Ecuador. For 12 dry- to communityfloristic diversity are verycon- forest sites there was not a single repeat of sistent.Perhaps the familyis the basic unit a 'most dominant" species. on whichselection for low population densities Even if all 213 species that are dominant (and thusindirectly for high species richness) or subdominant in any of these samples (i.e., occurs. For example, many seed predators among the most common 5-10 species) are and leaf-eatinginsects are host-specificat the considered, only 38 are repeated in two or generic or familial,as well as the specific, more differentsamples; ten of these repeated level (Janzen,1975, 1980, 1984). If family- common species (13 if Rio Palenque and Cen- specificpredators and/or family-specific com- tinela are considered part of the same site) petitionare added to the scenarioof dynamic are in repeat samples of the same forest. forestswith some nichedifferentiation, an ex- Thus, only 24 species are abundant at more planationpleasing to selectionistsand non- than one site. One species, Socratea exor- selectionistsalike could begin to take shape. rhiza, is abundant at four sites, and three As indicatedin Table 1, the familialdiversity species jessenia bataua, Arrabidaea ox- of tropicalmoist and wet forests,unlike the ycarpa, and Arrabidaea pubescens -are species richness,is bothhigh and remarkably abundant at three sites. Ten of the 24 species constant.It is certainlywithin the realm of abundant at more than one site are shared possibilitythat this is due to ca. 50 family- between different dry forests, twelve are specificniches in a givenforest, whereas the shared between differentmoist forests (typi- differingspecies richnessof differentforests cally between Central America and Amazon- could be largelystochastically generated by ia), and one (Mansoa verrucifera) is abundant factorsrelating to higherturnover in themore in one dry-forestand in one moist-forestsite. species-richsites on bettersoils and withhigher A major part of the debate on whether productilvities. tropical-forestecosystems are at equilibrium A differenttype of reconciliation,espe- or nonequilibriummay be a by-productof the cially of the differencesbetween upper Am- scale of a particular study or the focus of a azonian and CentralAmerican species rich- particular author. The "rare" species that ness, theircauses, and the equilibriumstatus "random walk" through a 50-ha plot on Bar- of the forestsinvolved, might come froma ro Colorado Island-are -mostlycommon under- differentapproach to the data. Hubbell & storyor second growthspecies that would be Foster (1986) emphasizedthat niche differ-- regarded as permanent an-dcontinuous memn entiationamong Barro Colorado Island species bers of the more comprehensive moist-forest seems to consist mostlyof separationinto Volume 75, Number1 Gentry 31 1988 Plant CommunityDiversity abouta dozengeneralized multi-species guilds intodifferent communities may be completely based on degreeof shade toleranceand pref- random. erence foredaphic or topographicmicrosites. Indeed they suggestthat lack of niche dif- ferentiationmight make possible the co-oc- LITERATURE CITED currenceof many potential competitors which ASHTON, P. 1964. 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