Shifts in species and phylogenetic diversity between sapling and tree communities indicate negative density dependence in a lowland rain forest

Authors

  • Mailyn A. Gonzalez,

    Corresponding author
    1. Laboratoire Evolution et Diversité Biologique, UMR 5174 Université Paul Sabatier/CNRS, Bâtiment 4R3, Université Paul Sabatier, 31062 Toulouse, France
      *Correspondence author. E-mail: gonzalez.mailyn@gmail.com
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  • Aurélien Roger,

    1. Laboratoire Evolution et Diversité Biologique, UMR 5174 Université Paul Sabatier/CNRS, Bâtiment 4R3, Université Paul Sabatier, 31062 Toulouse, France
    2. Department of Ecology and Evolution, Biophore, University of Lausanne, 1015 Lausanne, Switzerland
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  • Elodie A. Courtois,

    1. Laboratoire Evolution et Diversité Biologique, UMR 5174 Université Paul Sabatier/CNRS, Bâtiment 4R3, Université Paul Sabatier, 31062 Toulouse, France
    2. CNRS, UMR Ecofog, Université Antilles Guyane, BP 709, 97387 Kourou Cedex, France
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  • Franck Jabot,

    1. Laboratoire Evolution et Diversité Biologique, UMR 5174 Université Paul Sabatier/CNRS, Bâtiment 4R3, Université Paul Sabatier, 31062 Toulouse, France
    2. AgroParisTech ENGREF, 19 Avenue du Maine, 75732 Paris, France
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  • Natalia Norden,

    1. Laboratoire Evolution et Diversité Biologique, UMR 5174 Université Paul Sabatier/CNRS, Bâtiment 4R3, Université Paul Sabatier, 31062 Toulouse, France
    2. Department of Ecology and Evolutionary Biology, University of Connecticut, 75 North Eagleville Road, Storrs, CT 06269-3034, USA
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  • C. E. Timothy Paine,

    1. ENGREF, UMR EcoFog, 97387 Kourou Cedex, France
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  • Christopher Baraloto,

    1. INRA, UMR EcoFog, 97387 Kourou Cedex, France
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  • Christophe Thébaud,

    1. Laboratoire Evolution et Diversité Biologique, UMR 5174 Université Paul Sabatier/CNRS, Bâtiment 4R3, Université Paul Sabatier, 31062 Toulouse, France
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  • Jérôme Chave

    1. Laboratoire Evolution et Diversité Biologique, UMR 5174 Université Paul Sabatier/CNRS, Bâtiment 4R3, Université Paul Sabatier, 31062 Toulouse, France
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*Correspondence author. E-mail: gonzalez.mailyn@gmail.com

Summary

1. As trees in a given cohort progress through ontogeny, many individuals die. This risk of mortality is unevenly distributed across species because of many processes such as habitat filtering, interspecific competition and negative density dependence. Here, we predict and test the patterns that such ecological processes should inscribe on both species and phylogenetic diversity as plants recruit from saplings to the canopy.

2. We compared species and phylogenetic diversity of sapling and tree communities at two sites in French Guiana. We surveyed 2084 adult trees in four 1-ha tree plots and 943 saplings in sixteen 16-m2 subplots nested within the tree plots. Species diversity was measured using Fisher’s alpha (species richness) and Simpson’s index (species evenness). Phylogenetic diversity was measured using Faith’s phylogenetic diversity (phylogenetic richness) and Rao’s quadratic entropy index (phylogenetic evenness). The phylogenetic diversity indices were inferred using four phylogenetic hypotheses: two based on rbcLa plastid DNA sequences obtained from the inventoried individuals with different branch lengths, a global phylogeny available from the Angiosperm Phylogeny Group, and a combination of both.

3. Taxonomic identification of the saplings was performed by combining morphological and DNA barcoding techniques using three plant DNA barcodes (psbA-trnH, rpoC1 and rbcLa). DNA barcoding enabled us to increase species assignment and to assign unidentified saplings to molecular operational taxonomic units.

4. Species richness was similar between saplings and trees, but in about half of our comparisons, species evenness was higher in trees than in saplings. This suggests that negative density dependence plays an important role during the sapling-to-tree transition.

5. Phylogenetic richness increased between saplings and trees in about half of the comparisons. Phylogenetic evenness increased significantly between saplings and trees in a few cases (4 out of 16) and only with the most resolved phylogeny. These results suggest that negative density dependence operates largely independently of the phylogenetic structure of communities.

6.Synthesis. By contrasting species richness and evenness across size classes, we suggest that negative density dependence drives shifts in composition during the sapling-to-tree transition. In addition, we found little evidence for a change in phylogenetic diversity across age classes, suggesting that the observed patterns are not phylogenetically constrained.

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