The supplement is a script (R_script_simulation.r) demonstrating the implementation of our simulations and subsequent analysis of asymmetry. The simulation method we utilized is nonparametric and user-defined. For this reason we have included the script. As described in the methods section of our associated manuscript, the simulation involves imposing species extinctions in our post-mixing communities and using the output as a null model against which we compare our observed results. The script includes annotations describing the function of each section of code.