Disentangling community functional components in a litter-macrodetritivore model system reveals the predominance of the mass ratio hypothesis

Authors

  • Karolína Bílá,

    Corresponding author
    1. Community Ecology, Swiss Federal Research Institute WSL, Bellinzona, Switzerland
    2. Department of Biodiversity Research, Divison of Ecosystems Analysis, Global Change Research Centre AS CR, České Budějovice, Czech Republic
    • Correspondence

      Karolína Bílá, Swiss Federal Research Institute WSL, Community Ecology, Via Belsoggiorno 22, 6500 Bellinzona, Switzerland. Tel: +41 91 8215 230; Fax: +41 91 8215 239;

      E-mail: kcerna@volny.cz

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  • Marco Moretti,

    1. Community Ecology, Swiss Federal Research Institute WSL, Bellinzona, Switzerland
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  • Francesco de Bello,

    1. Institute of Botany, Czech Academy of Sciences, Třeboň, Czech Republic
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  • André T.C. Dias,

    1. Department of Ecological Science, Faculty of Earth and Life Sciences, VU University Amsterdam, Amsterdam, the Netherlands
    2. Departamento de Ecologia, Instituto de Biologia Roberto Alcantara Gomes, Universidade do Estado do Rio de Janeiro – UERJ, Rio de Janeiro, RJ, Brasil
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  • Gianni B. Pezzatti,

    1. Community Ecology, Swiss Federal Research Institute WSL, Bellinzona, Switzerland
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  • Arend Raoul Van Oosten,

    1. Community Ecology, Swiss Federal Research Institute WSL, Bellinzona, Switzerland
    2. Department of Ecological Science, Faculty of Earth and Life Sciences, VU University Amsterdam, Amsterdam, the Netherlands
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  • Matty P. Berg

    1. Department of Ecological Science, Faculty of Earth and Life Sciences, VU University Amsterdam, Amsterdam, the Netherlands
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Abstract

Recent investigations have shown that two components of community trait composition are important for key ecosystem processes: (i) the community-weighted mean trait value (CWM), related to the mass ratio hypothesis and dominant trait values in the community, and (ii) functional diversity (FD), related to the complementarity hypothesis and the divergence of trait values. However, no experiments controlling for the inherent dependence between CWM and FD have been conducted so far. We used a novel experimental framework to disentangle the unique and shared effects of CWM and FD in a leaf litter-macrodetritivore model system. We manipulated isopod assemblages varying in species number, CWM and FD of litter consumption rate to test the relative contribution of these community parameters in the decomposition process. We showed that CWM, but also the combination of CWM and FD, is a main factor controlling litter decomposition. When we tested individual biodiversity components separately, CWM of litter consumption rate showed a significant effect on decomposition, while FD and species richness alone did not. Our study demonstrated that (i) trait composition rather than species diversity drives litter decomposition, (ii) dominant trait values in the community (CWM) play a chief role in driving ecosystem processes, corroborating the mass ratio hypothesis, and (iii) trait dissimilarity can contribute in modulating the overall biodiversity effects. Future challenge is to assess whether the generality of our finding, that is, that dominant trait values (CWM) predominate over trait dissimilarity (FD), holds for other ecosystem processes, environmental conditions and different spatial and temporal scales.

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