PT  - JOURNAL ARTICLE
AU  - Logan M. Higgins
AU  - Jonathan Friedman
AU  - Hao Shen
AU  - Jeff Gore
TI  - Co-occurring soil bacteria exhibit a robust competitive hierarchy and lack of non-transitive interactions
AID  - 10.1101/175737
DP  - 2017 Jan 01
TA  - bioRxiv
PG  - 175737
4099  - http://biorxiv.org/content/early/2017/08/16/175737.short
4100  - http://biorxiv.org/content/early/2017/08/16/175737.full
AB  - Microbial communities are typically incredibly diverse, and this diversity is thought to play a key role in community function. However, explaining how this diversity can be maintained is a major challenge in ecology. Temporal fluctuations and spatial structure in the environment likely play a key role, but it has also been suggested that the structure of interactions within the community may act as a stabilizing force for species diversity. In particular, if competitive interactions are non-transitive as in the classic rock-paper-scissors game, they can contribute to the maintenance of species diversity; on the other hand, if they are predominantly hierarchical, any observed diversity must be maintained via other mechanisms. Here, we investigate the network of pairwise competitive interactions in a model community consisting of 20 strains of naturally co-occurring soil bacteria. We find that the interaction network is strongly hierarchical and lacks significant non-transitive motifs, a result that is robust across multiple environments. Moreover, in agreement with recently proposed community assembly rules, the full 20-strain competition resulted in extinction of all but three of the most highly competitive strains, indicating that higher order interactions do not play a major role in structuring this community. The lack of non-transitivity and higher order interactions in vitro indicates that other factors, such as temporal or spatial heterogeneity, must be at play in enabling these strains to coexist in nature.