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Density dependence explains tree species abundance and diversity in tropical forests


The recurrent patterns in the commonness and rarity of species in ecological communities—the relative species abundance—have puzzled ecologists for more than half a century1,2. Here we show that the framework of the current neutral theory in ecology3,4,5,6,7,8,9,10 can easily be generalized to incorporate symmetric density dependence11,12,13,14. We can calculate precisely the strength of the rare-species advantage that is needed to explain a given RSA distribution. Previously, we demonstrated that a mechanism of dispersal limitation also fits RSA data well3,4. Here we compare fits of the dispersal and density-dependence mechanisms for empirical RSA data on tree species in six New and Old World tropical forests and show that both mechanisms offer sufficient and independent explanations. We suggest that RSA data cannot by themselves be used to discriminate among these explanations of RSA patterns15—empirical studies will be required to determine whether RSA patterns are due to one or the other mechanism, or to some combination of both.

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Figure 1: Fits of density-dependent symmetric model (red line) and dispersal-limitation model 3 (blue circles) to the tree species abundance data from the BCI, Yasuni, Pasoh, Lambir, Korup and Sinharaja plots, for trees ≥10 cm in stem diameter at breast height (see Table 1).
Figure 2: Test of the equivalence of the dispersal limitation model and the density-dependent symmetric model.
Figure 3: Plot of n derived from equation (1) versus n for the six data sets of tropical trees.


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We are indebted to D. Alonso and P. Chesson for advice. We gratefully acknowledge the work of the principal investigators and their field assistants for collecting the field data on the large plots of tropical forest. Specifically, we thank D. Thomas, G. Chuyong and D. Kenfack for the data from Korup National Park, Cameroon; R. Valencia, R. Foster and R. Condit for the data from Yasuni National Park, Ecuador; S. Davies, S. Tan, J. LaFrankie and P. Ashton for the data from Lambir Hills National Park, Sarawak; M. N. Supardi, P. Ashton and J. LaFrankie for the data from Pasoh Forest Reserve, peninsular Malaysia; and S.P.H.'s collaborators on the Barro Colorado Island plot, R. Foster and R. Condit. We also thank E. Losos for directing and coordinating the global programmes of the Center for Tropical Forest Science, which manages the plots, S. Loo for data management, and I. Rubinoff. This work was supported by NASA, by the NSF and the NSERC (Canada). The fieldwork has also received long-term support from the John D. and Catherine T. MacArthur Foundation, the Mellon Foundation, Earthwatch, Frank Levinson and the Celera Foundation, and other private foundations and individual donors.

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Correspondence to Jayanth R. Banavar.

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Supplementary Notes

This file contains Supplementary Discussion and Supplementary Figure 1. (PDF 102 kb)

Supplementary Data*

This file includes additional data from the study. *This file was uploaded on 08 December 2005, as was erroneously omitted from original publication. (XLS 408 kb)

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Volkov, I., Banavar, J., He, F. et al. Density dependence explains tree species abundance and diversity in tropical forests. Nature 438, 658–661 (2005).

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