Strong interdependence generates communities that are robust to variation in initial conditions.

Abstract

<p><b>A, B,</b> Emergent population structure (segregation index, <i>s</i>_A,) as a function of initial intermixing, for two scenarios. <b>A</b>, strong interdependence (i.e. obligate cross-feeding and high by-product toxicity) and <b>B</b>, no interdependence (control scenario). Population structure is recorded at inoculation (open circles), and after 12 (grey dots) and 96 (black dots) hours. Initial population structure was varied by varying the proportions of producer (species A) and cross-feeder cells (species B) in two adjacent micro-colonies (of size 30 µm separated by a distance of 70 µm) while maintaining a constant total inoculation density and ratio (1∶1). An initial segregation 0 means that each microcolony received equal numbers of A and B, whereas initial segregation of 1 means that one microcolony was pure A and the other pure B. An increment in initial segregation of 0.1 means a 5% increase (or decrease) in the number of cells of species A (or species B) inoculated in each microcolony. <b>C, D.</b> Proportion of producers as a function of initial producer proportion for strong interdependence (i.e. obligate cross-feeding and high by-product toxicity) and control scenario, respectively, and after 12 (grey dots) and 96 (black dots) hours growth (initial segregation = 0). Data are the mean of 3 replicates and error bars are the SD of the mean.</p