Fig. 6. FMT strain-level outcomes are shaped by both neutral and adaptive processes.

Each of the tested variables used to predict FMT outcome can be linked to putative underlying ecological processes, as suggested previously³³. Factors are organized by scope (pertaining to the donor, recipient or donor–recipient complementarity, top) and resolution (host, community, species and strain level; left to right). Underlying ecological processes can be roughly ranked along the gradient, from neutral/stochastic to adaptive/selective; each process is illustrated with a toy example on the right. Circle size corresponds to average variable importance, calculated across all tested species from LASSO coefficients and overall model performance (less predictive models penalize variable importance). Recipient factors and, in particular, donor–recipient complementarity measures across all resolutions, were generally far more relevant to species-level outcome than donor factors. neg, negative; pos., positive; abd, abundance.