The effects of ecological selection on species diversity and trait distribution: predictions and an empirical test

Niv DeMalach*, Po Ju Ke, Tadashi Fukami

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

2 Scopus citations


Ecological selection is a major driver of community assembly. Selection is classified as stabilizing when species with intermediate trait values gain the highest reproductive success, whereas selection is considered directional when fitness is highest for species with extreme trait values. Previous studies have investigated the effects of different selection types on trait distribution, but the effects of selection on species diversity have remained unclear. Here, we propose a framework for inferring the type and strength of selection by studying species diversity and trait distribution together against null expectations. We use a simulation model to confirm our prediction that directional selection should lead to lower species diversity than stabilizing selection despite a similar effect on trait community-weighted variance. We apply the framework to a mesocosm system of annual plants to test whether differences in species diversity between two habitats that vary in productivity are related to differences in selection on seed mass. We show that, in both habitats, species diversity was lower than the null expectation, but that species diversity was lower in the more productive habitat. We attribute this difference to strong directional selection for large-seeded species in the productive habitat as indicated by trait community-weighted mean being higher and community-weighted variance being lower than the null expectations. In the less productive habitat, we found that community-weighted variance was higher than expected by chance, suggesting that seed mass could be a driver of niche partitioning under such conditions. Altogether, our results suggest that viewing species diversity and trait distribution as interrelated patterns driven by the same process, ecological selection, is helpful in understanding community assembly.

Original languageAmerican English
Article numbere03567
Issue number1
StatePublished - Jan 2022

Bibliographical note

Funding Information:
We thank Ronen Ron and Ronen Kadmon for contributing data from their mesocosm experiment. Karen Abbott, Matthieu Barbier, Gili Greenbaum, Susan Harrison, an anonymous reviewer, and the members of the community ecology group at Stanford University provided constructive comments on earlier drafts. This work was supported by the Rothschild fellowship (N. DeMalach), the Terman Fellowship of Stanford University (T. Fukami), and the studying abroad scholarship of the Ministry of Education of Taiwan (P.‐J. Ke). Author contributions: N. DeMalach, P.‐J. Ke, and T. Fukami conceived and designed the framework and analyses; N. DeMalach performed the simulation and empirical analyses; N. DeMalach wrote the first draft; all authors substantially contributed to the writing of the manuscript.

Publisher Copyright:
© 2021 by the Ecological Society of America

© 2021 by the Ecological Society of America.


  • Biodiversity
  • Ecosystem
  • Phenotype
  • Plants
  • Reproduction
  • Seeds


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