The consequences of plant–plant interactions at the community level: A niche-based approach

Background/Question/Methods

Biodiversity is a fundamental requisite for life on earth. Major efforts have been made to understand species coexistence and the regulation of biodiversity. However, there is no general consensus on the effects of plant communities on their diversity, or a holistic conceptual model to predict such effects. We used an experimental approach manipulating genotype and species composition and diversity in synthetic plant communities, and we developed a novel analytical approach based on the niche concept to understand the processes underlying counter-balancing positive and negative effects of plants on plant diversity.

Results/Conclusions

We demonstrated significant reductions in the establishment of “new” plant species added to experimental plant communities when species richness of these communities increased, but not when genotype richness increased. Reduced susceptibility to invasion of more species-rich communities was due to increased niche space consumption, which affected in particular the establishment of rare species. Rare species responded much more strongly – in particular negatively but also positively – to the abiotic and biotic environmental engineering effects of the experimental communities. Common species appeared to occupy mostly unexploited niche space, explaining their commonness. In contrast, rare species showed stronger impacts of neighbours, strongly suffering from competitive exclusion and benefiting from facilitative effects. Our approach  – differentiating between niche space consumption and construction and the characteristics of responding organisms – constitutes a crucial development for niche theory. Our study shows that combining competition and facilitation within coexistence theory helps to explain the self-regulating nature of plant communities on their diversity.