Resident populations
Ancestral Pseudomonas fluorescens SBW25 was grown overnight to carrying capacity in shaken glass vials (microcosms) containing 6mL of King’s medium B (KB) at 28°C. Sixty microliters of this culture was then transferred into static microcosms containing KB of varying concentrations (100% KB, 10% or 1%) to create different resource abundances; KB was diluted with M9 salt solution (3g KH2PO4, 6g Na2HPO4, 5g NaCl L-1). Microcosms were disturbed every 1, 2, 4, 8 or 16 days (Fig. 1) by transferring 1% of homogenised broth into fresh media (99% mortality) for a total of 16 days. Invaders were inoculated at days 4, 8 and 12 (Fig. 1 and see Invasions below). In between transfers and invasions, all microcosms were kept static at 28°C with loose lids to allow oxygen transfer. We used 12 replicates of each resource abundance (3) and disturbance frequency (5) combination, for a total of 180 microcosms. Additional microcosms (n=3 per resource abundance x disturbance combination) were set up to quantify resident density on day 4 – the first invasion time point. This was necessary as the sampling microcosms required homogenisation of treatments that would otherwise not be disturbed.