Estimates of microbial community stability using relative invader growth rates are robust across levels of invader species richness.

A key feature of natural communities is that the species within them stably coexist. A common metric used to test community stability is the ability of each species to invade from rare. A potential issue with this measurement is that single species are invaded from rare, while in natural communities, multiple species would likely decline simultaneously following perturbations. This is especially common in microbes which can be rapidly disturbed by environmental stressors. If species coexistence is dependent on indirect interactions among community members, multiple species declining may result in community instability. As such, invading a single species into a community may overestimate the stability of a community when multiple species decline. Here, we compare estimates of community stability in a five species microbial community to experimental results in which multiple species are simultaneously invaded. Our results showed that single species invasions were qualitatively predictive of whole community stability when multiple species are invaded simultaneously. However, quantitative values of relative invader growth rate were less comparable, being non-significantly different in most comparisons in three out of five species. This was emphasized by the lack of correlation between exact values of growth rates under single or multi-species invasion. This work provides experimental support for the robustness of using invasion growth rate of single species to infer qualitative estimates of community stability.