Theoretical and empirical ecological studies have shown that biodiversity is a key component to maintaining the functioning of ecosystems across temporal environmental variations. Species communities are also dynamic in their responses to changes in their local environment and their competitive interactions with neighboring species that contribute to the stability at community level. However, the significance of competition and its importance in the stability of more diverse plant communities has been severely limited by the lack of empirical data so far. We hypothesize that between-species competition plays a greater role in stabilizing community performance in more diverse communities.
The study took place in the long-term Jena Experiment (2003–2015) where nine plant species were grown in monocultures and in all possible pairs occurring in communities of increasing species richness (2, 3, 4, 6 and 9). Annual productivity of each plant species in every community was measured over the period. Pairwise interspecific interaction coefficients were determined for each species in a community using Lotka-Volterra competition models. Competitive interactions with increasing diversity were then used to infer a mechanistic understanding of how competition and diversity interactively stabilized communities.
The overall competitive pressure experienced by particular species generally increased with diversity. However, the competitive disparity between a particular species and its neighbors generally declined with diversity with the exception of one particularly dominant species that contributed to over 70% of the net community productivity when present. Although the presence of a particular dominant species resulted in greater competitive exclusions it also maintained a more stability community productivity over the years, but had a little influence on the population level dynamics. Conversely, greater competitive symmetry within a community resulted in fewer competitive exclusions, greater temporal asynchrony and evenness, but had no overall influence on the stability in the communities net productivity. Our study reveals the differing roles of competitive dominance and competitive symmetry in shaping the long-term community composition and functioning. We conclude that greater biodiversity is necessary to provide opportunities for competition to shape community assembly in response to temporal environmental change.