Ecological role structures community function more than species identity in synthetic sourdough communities

We tested this using synthetic sourdough communities (SynComs) assembled from a defined species pool established in our earlier work, in which single species were exchanged for another occupying the same role, while composition and inoculum density were held constant.

Across eighteen primary perturbation SynComs, ecological role explained 38.7% of variance in backbone metatranscriptome expression (pseudo F = 8.38, p = 0.0006), while the secondary condition (satellite or yeast substitution) and its interaction with role did not reach significance. Dominant lactic acid bacteria accounted for 95 to 99% of pooled transcript output regardless of which species occupied that role. Species identity itself still explained 87.7% of variance within a single role (pseudo F = 28.44, p = 0.10, the exact enumeration floor of this design), so role and identity act together rather than one replacing the other.