Fig. 4

Tradeoff between growth and competitive ability leads to dependence of experimental outcome on dilution factor. The LV model predicts that increasing dilution will favor faster-growing species over slower-growing ones. If fast growers dominate at low dilution factors, though, no changes in outcome will be expected. Changes in outcome are therefore most dramatic when slow growers are strong competitors at low dilution, exhibiting a tradeoff between growth rate and competitive ability. a This tradeoff was pervasive in our system: slower growth rates resulted in higher competitive scores at the lowest dilution factor. Growth rate was calculated with OD600 measurements of the time taken for monocultures to reach a threshold density within the exponential phase; error bars represent the SEM of replicates (n = 21, per species) (Supplementary Fig. 3). Competitive score was calculated by averaging fraction of a given species across all pairwise competitive outcomes; error bars were calculated by bootstrapping, where replicates of mean experimental outcomes of a given pair were sampled 5000 times with replacement (n = 34, per species, per dilution factor). b The competitive scores in a are extended to all dilution factors. The slowest grower’s score monotonically decreases with dilution, while the fast growers’ scores increase, and an intermediate grower peaks at intermediate dilution factor. A similar pattern was seen in data from experiments in a complex growth medium (Supplementary Fig. 7). c At high dilution factors, the order of scores is reversed. d At low dilution factors 10 and 10², competitive ability is negatively correlated with growth rate; the correlation becomes positive above dilution factor 10³. Error bars are the standard error coefficients given by the linear regression function lm in R. Source data are provided as a Source Data file