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Tree densities and sex ratios in breeding populations of dioecious Central Amazonian Myristicaceae

Published online by Cambridge University Press:  10 July 2009

David D. Ackerly
Affiliation:
World Wildlife Fund - US, Washington, DC, USA
Judy M. Rankin-De-Merona
Affiliation:
Departamento de Ecologia, Instituto Nacional de Pesquisas da Amazônia, Manaus, Brazil
William A. Rodrigues
Affiliation:
Departamento de Botânica, Instituto Nacional de Pesquisas da Amazônia, Manaus, Brazil

Abstract

The densities of the breeding populations and the sex of all flowering individuals were recorded for five dioecious canopy tree species of Central Amazonian Myristicaceae, in 11 study areas of the Minimum Critical size of Ecosystems Project totalling 22.5 ha. Adult population densities were extremely low, ranging from 0.38 to 1.61 ha–1 for the five species studied. In a 10 ha study plot the mean distance to the nearest flowering conspecific ranged from 48 to 100 m, while the mean distance to the nearest opposite sex conspecific was 147 m. The two most abundant species, Iryanthera macrophylla and Virola calophylla, both showed male-biased sex ratios, of 23:9 and 20:6, respectively. The size class distribution of males, females and non-flowering individuals in V. calophylla suggests that earlier reproductive maturation of male plants may provide a partial explanation for this bias. In I. macrophylla, since 95% of the individuals were observed flowering, the observed ratio is representative of the population, and may be caused by sex shifts from male to female. The low reproductive densities, combined with the skewed sex ratios and overlapping generations of these species, create very small effective breeding populations, placing species such as these at great risk in the face of deforestation and habitat fragmentation.

RESUMO. [Densidades de árvores e razāo dos sexos em populações reprodutivas de espécies dióicas da família Myristicaceae na Amazônia Central.]

Foi realizado um Ievantamento da densidade de indivíduos adultos e do sexo de todos os indivíduos reprodutivos, para cinco espécies de árvores dióicas da família Myristicaceae. O estudo foi densenvolvido em 22,5 ha distribuídos por onze reservas biológicas na Amazônia Central dentro do Projeto de Dinámicas Biolótricas de Fragmentos Florestais. A densidade das populaçōes foi extremamente baixa.de 0,38 a 1,61 árvores ha−1, para as cinco espécies estudadas. A distância média ao coespecinco mais proximo foi de 48 a 100 m, enquanto a distância média ao coespecífico do sexo oposto mais próximo atingiu valores de até 147 m. As duas espécies mais abundantes, Iryanthera macrophylla e Virola calophylla, apresentaram razões de sexos de 23:9 e 20:6 respectivamente, com uma clara predominância de indivíduos masculinos. A distribuiçao de classes de tamanho para ambos os sexos e de indivíduos não reprodutivos em V. calophylla sugere que o amadurecimento precoce dos indivíduos masculinos seja uma das razões para a dominancia dos mesmos. Em I. macrophylla, uma vez que 95% dos indivíduos floresceram, a razãb de sexos observada é representitiva da população, e pode ser causada por mudançãs sexuais de uma fase masculina para uma fase feminina. As baixas densidades de indivíduos reprodutivos, àliadas às diferenças nas razões de sexos e à sobreposição de gerações, reduzem muito o tamanho efetivo das populações reprodutivas, colocando espécies como estas em alto risco de extinção, devido ao desmatamento e à fragmentação de seus habitats.

Type
Research Article
Copyright
Copyright © Cambridge University Press 1990

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References

LITERATURE CITED

Armstrong, J. E. & Drummond, B. A. 1986. Floral biology of Myristica fragrans Houtt. (Myristi-caceae), the nutmeg of commerce. Biotropica 18:3238.CrossRefGoogle Scholar
Armstrong, J. E. & Irvine, A. K. 1989a. Flowering, sex ratios, pollen-ovule ratios, fruit set, and reproductive effort of a dioecious tree, Myristica insipida (Myristicaceae), in two different rain forest communities. American Journal of Botany 76:7485.CrossRefGoogle Scholar
Armstrong, J. E. & Irvine, A. K. 1989b. Floral biology of Myristica insipida (Myristicaceae), a distinctive beetle pollination syndrome. American Journal of Botany 76:8694.CrossRefGoogle Scholar
Bawa, K. S. 1980. Evolution of dioecy in flowering plants. Annual Review of Ecology and Systematics 11:1539.Google Scholar
Bawa, K. S. & Opler, P. A. 1975. Dioecism in tropical forest trees. Evolution 29:167179.CrossRefGoogle ScholarPubMed
Bawa, K. S. & Opler, P. A. 1977. Spatial relationships between staminate and pistillate plants of dioecious tropical forest trees. Evolution 31:6468.Google Scholar
Bawa, K. S., Perry, D. R. & Beach, J. H. 1985a. Reproductive biology of tropical lowland rain forest trees. I. Sexual systems and self-incompatibility mechanisms. American Journal of Botany 72:331345.Google Scholar
Bawa, K. S., Perry, D. R., Bullock, S. H., Coville, R. E. & Grayum, M. H. 1985b. Reproductive biology of tropical lowland rain forest trees. II. Pollination mechanisms. American Journal of Botany 72:346356.Google Scholar
Bullock, S. H. 1985. Breeding systems in the flora of a tropical deciduous forest in Mexico. Biotropica 17:287301.Google Scholar
Bullock, S. H., Beach, J. H. & Bawa, K. S. 1983. Episodic flowering and sexual dimorphism in Guarea rhopalocarpa in a Costa Rican rain forest. Ecology 64:851861.Google Scholar
Charnov, E. L. 1982. The theory of sex allocation. Princeton University Press, Princeton, NJ.Google Scholar
Ducke, A. 1950. Plantas novas ou poucas conhecidas da Amazônia. Boletím técnico do Instituto Agronômico do Norte 19:342.Google Scholar
Flach, M. 1966. Nutmeg cultivation and its sex problem. Mededelingen van de Landbouwhogeschool Wageningen 661:185.Google Scholar
Franklin, I. R. 1980. Evolutionary change in small populations. Pp. 135–149 in Soulé, M. E. & Wilcox, B. A. (eds). Conservation biology: an evolutionary-ecological perspective. Sinauer Assoc., Sunderland, Massachusetts.Google Scholar
Freeman, D. C., Harper, K. T. & Charnov, E. L. 1980. Sex change in plants: old and new observations and hypotheses. Oecologia 42:222232.Google Scholar
Gilpin, M. E. & Soulé, M. E. 1986. Minimum viable populations: Processes of species extinction. Pp. 19–34 in Soulé, M. E. (ed.). Conservation biology: The science of scarcity and diversity. Sinauer Assoc., Sunderland, Massachusetts.Google Scholar
Heywood, V. H. (ed.). 1978. Flowering plants of the world. Oxford University Press, Oxford.Google Scholar
Hubbell, S. P. 1979. Tree dispersion, abundance, and diversity in a tropical dry forest. Science 203:12991309.Google Scholar
Hubbell, S. P. & Foster, R. B. 1986. Commonness and rarity in a neotropical forest: implications for tropical tree conservation. Pp. 205–231 in Soulé, M. E. (ed.). Conservation biology: The science of scarcity and diversity. Sinauer Assoc., Sunderland, Massachusetts.Google Scholar
Lande, R. & Barrowclough, G. F. 1987. Effective population size, genetic variation, and their use in population management. Pp. 87–123 in Soulé, M. E. (ed.). Viable populations for conservation. Cambridge University Press, Cambridge.Google Scholar
Levin, D. A. & Kerster, H. W. 1974. Gene flow in seed plants. Evolutionary Biology 7:139220.Google Scholar
Lieberman, D. & Lieberman, M. 1987. Forest tree growth and dynamics at La Selva, Costa Rica (1969–1982). Journal of Tropical Ecology 3:347358.Google Scholar
Lovejoy, T. E.Bierregaard, R. O., Rylands, A. B., Malcolm, J. R., Quintela, C. E.Harper, L. H., Brown, K. S., Powell, A. H., Powell, G. V. N., Schubart, H. O. R. & Hays, M. B. 1986. Edge and other effects of isolation on Amazon forest fragments. Pp. 257–285 in Soulé, M. E. (ed.). Conservation biology: The science of scarcity and diversity. Sinauer Assoc., Sunderland, Massachusetts.Google Scholar
Lloyd, D. G. 1973. Sex ratios in sexually dimorphic Umbelliferae. Heredity 31:239249.CrossRefGoogle Scholar
Lloyd, D. G. & Bawa, K. S. 1984. Modification of the gender of seed plants in varying conditions. Evolutionary Biology 17:255338.Google Scholar
Marques Filho, A. de O., Ribeiro, M. de N. G., Santos, H. M. dos & Santos, J. M. dos. 1981. Estudos climatològicos da Reserva Florestal Ducke - Manaus - AM. IV. Precipitação. Acta Amazônica 11:759768.Google Scholar
Opler, P. A. & Bawa, K. S. 1978. Sex ratios in some tropical forest trees. Evolution 32:812821.Google Scholar
Rankin-de-Merona, J. M. & Ackerly, D. D. 1987. Estudos populacionais de arvores em florestas fragmentadas e as implicações para conservação in situ das mesmas na floresta tropical de Amazonia Central. Instituto de Pesquisas e Estudos Florestais da Escola Superior de Agricultura ‘Luiz de Quei-roz’, Untversidade de Sao Paulo, No. 35:4759, Piracicaba, Brazil.Google Scholar
Rankin-de-Merona, J. M., Prance, G. T., Silva, M. F., Rodrigues, W. A. & Uehling, M.Resultados preliminares de um levantamento florestal de 31 ha de terra firme na Amazônia Central: descrição geral da vegetação e dados taxonòmicos. Acta Amazônica, in press.Google Scholar
Rathore, J. S. 1969. Distribution patterns of male and female plants of Diospyros melanoxylon Roxb. in the forests of Sagar, M. P. Indian Forester 96:701.Google Scholar
Rodrigues, W. A. 1980. Revisão taxonomica das espècies de Virola Aublet (Myristicaceae) do Brasil. Acta Amazônica 10, Suppl.: 1127.Google Scholar
Smith, A. C. 1937. The American species of Myristicaceae. Brittonia 2:393510.Google Scholar
Soulé, M. E. 1980. Thresholds for survival: maintaining fitness and evolutionary potential. Pp. 151–170 in Soulé, M. E. & Wilcox, B. A. (eds). Conservation biology: an evolutionary-ecological perspective. Sinauer Assoc., Sunderland, Massachusetts.Google Scholar
Soulé, M. E. (ed.). 1987. Viable populations for conservation. Cambridge University Press, Cambridge.Google Scholar
Styles, B. T. 1972. The flower biology of the Meliaceae and its bearing on tree breeding. Silvae Gene-tica 21:175182.Google Scholar