Hyperdominance in the Amazonian Tree Flora
Authors: ter Steege Hans , Pitman Nigel C. A. , Sabatier Daniel , Baraloto Christopher , Salomão Rafael P. , Guevara Juan Ernesto , Phillips Oliver L. , Castilho Carolina V. , Magnusson William E. , Molino Jean-François , Monteagudo Abel , Núñez Vargas Percy , Montero Juan Carlos , Feldpausch Ted R. , Coronado Eurídice N. Honorio , Killeen Tim J. , Mostacedo Bonifacio , Vasquez Rodolfo , Assis Rafael L. , Terborgh John , Wittmann Florian , Andrade Ana , Laurance William F. , Laurance Susan G. W. , Marimon Beatriz S. , Marimon Ben-Hur , Guimarães Vieira Ima Célia , Amaral Iêda Leão , Brienen Roel , Castellanos Hernán , Cárdenas López Dairon , Duivenvoorden Joost F. , Mogollón Hugo F. , Matos Francisca Dionízia de Almeida , Dávila Nállarett , García-Villacorta Roosevelt , Stevenson Diaz Pablo Roberto , Costa Flávia , Emilio Thaise , Levis Carolina , Schietti Juliana , Souza Priscila , Alonso Alfonso , Dallmeier Francisco , Montoya Alvaro Javier Duque , Fernandez Piedade Maria Teresa , Araujo-Murakami Alejandro , Arroyo Luzmila , Gribel Rogerio , Fine Paul V. A. , Peres Carlos A. , Toledo Marisol , Aymard C. Gerardo A. , Baker Tim R. , Cerón Carlos , Engel Julien , Henkel Terry W. , Maas Paul , Petronelli Pascal , Stropp Juliana , Zartman Charles Eugene , Daly Doug , Neill David , Silveira Marcos , Paredes Marcos Ríos , Chave Jerome , Lima Filho Diógenes de Andrade , Jørgensen Peter Møller , Fuentes Alfredo , Schöngart Jochen , Cornejo Valverde Fernando , Di Fiore Anthony , Jimenez Eliana M. , Peñuela Mora Maria Cristina , Phillips Juan Fernando , Rivas Gonzalo , van Andel Tinde R. , von Hildebrand Patricio , Hoffman Bruce , Zent Eglée L. , Malhi Yadvinder , Prieto Adriana , Rudas Agustín , Ruschell Ademir R. , Silva Natalino , Vos Vincent , Zent Stanford , Oliveira Alexandre A. , Schutz Angela Cano , Gonzales Therany , Trindade Nascimento Marcelo , Ramirez-Angulo Hirma , Sierra Rodrigo , Tirado Milton , Umaña Medina María Natalia , van der Heijden Geertje , Vela César I. A. , Vilanova Torre Emilio , Vriesendorp Corine , Wang Ophelia , Young Kenneth R. , Baider Claudia , Balslev Henrik , Ferreira Cid , Mesones Italo , Torres-Lezama Armando , Urrego Giraldo Ligia Estela , Zagt Roderick , Alexiades Miguel N. , Hernandez Lionel , Huamantupa-Chuquimaco Isau , Milliken William , Palacios Cuenca Walter , Pauletto Daniela , Valderrama Sandoval Elvis , Valenzuela Gamarra Luis , Dexter Kyle G. , Feeley Ken , Lopez-Gonzalez Gabriela , Silman Miles R. 
Published: October 2013

IntroductionRecent decades have seen a major international effort to inventory tree communities in the Amazon Basin and Guiana Shield (Amazonia), but the vast extent and record diversity of these forests have hampered an understanding of basinwide patterns. To overcome this obstacle, we compiled and standardized species-level data on more than half a million trees in 1170 plots sampling all major lowland forest types to explore patterns of commonness, rarity, and richness.MethodsThe ~6-million-km2Amazonian lowlands were divided into 1° cells, and mean tree density was estimated for each cell by using a loess regression model that included no environmental data but had its basis exclusively in the geographic location of tree plots. A similar model, allied with a bootstrapping exercise to quantify sampling error, was used to generate estimated Amazon-wide abundances of the 4962 valid species in the data set. We estimated the total number of tree species in the Amazon by fitting the mean rank-abundance data to Fisher’s log-series distribution.ResultsOur analyses suggest that lowland Amazonia harbors 3.9 × 1011trees and ~16,000 tree species. We found 227 “hyperdominant” species (1.4% of the total) to be so common that together they account for half of all trees in Amazonia, whereas the rarest 11,000 species account for just 0.12% of trees. Most hyperdominants are habitat specialists that have large geographic ranges but are only dominant in one or two regions of the basin, and a median of 41% of trees in individual plots belong to hyperdominants. A disproportionate number of hyperdominants are palms, Myristicaceae, and Lecythidaceae.DiscussionThe finding that Amazonia is dominated by just 227 tree species implies that most biogeochemical cycling in the world’s largest tropical forest is performed by a tiny sliver of its diversity. The causes underlying hyperdominance in these species remain unknown. Both competitive superiority and widespread pre-1492 cultivation by humans are compelling hypotheses that deserve testing. Although the data suggest that spatial models can effectively forecast tree community composition and structure of unstudied sites in Amazonia, incorporating environmental data may yield substantial improvements. An appreciation of how thoroughly common species dominate the basin has the potential to simplify research in Amazonian biogeochemistry, ecology, and vegetation mapping. Such advances are urgently needed in light of the >10,000 rare, poorly known, and potentially threatened tree species in the Amazon.