Communities: are they groups of hidden interactions?

Questions Ecologists are increasingly interested in community‐level consequences of biotic interactions. However, community‐level studies have not considered that biotic interactions might have contrasting directions within communities, and indirect interactions are rarely quantified although they may influence community‐level outcomes. We tested the hypotheses that in species‐rich plant communities from intermediate severe environmental conditions: (1) direct facilitation by dominant functional groups is balanced by negative indirect interactions among beneficiary species with no net effect at the community level on diversity and biomass, and (2) both direct and indirect interactions contribute to community composition. Location A species‐rich subalpine community of the eastern T ibet P lateau ( C hina). Methods We removed dominant shrubs and graminoids and quantified, at the community and species levels, their direct and indirect effects on 43 forb species. We used multivariate analyses to assess the contribution of direct and indirect effects on community composition. Results There were no community‐level effects of either dominant life form on forb diversity and biomass. There were multiple species‐level interactions that we grouped into six types based on the direction and intensity of indirect effects. We found significant relationships between species‐level interactions and community composition. Conclusions Our study highlights that communities are sets of hidden interactions that contribute to community composition, although no interaction might be detected at the community level because hidden interactions balance each other. Future studies should assess the ecological and functional drivers of these hidden interactions.