Background: The ability of a bacterial strain to competitively exclude or displace other strains can be attributed to the production of narrow spectrum antimicrobials, the bacteriocins. In an attempt to evaluate the importance of bacteriocin production for Escherichia coli strain residence in the gastrointestinal tract, a murine model experimental evolution study was undertaken. Results: Six colicin-producing, yet otherwise isogenic, E. coli strains were administered and established in the large intestine of streptomycin-treated mice. The strains' persistence, population density, and doubling time were monitored over a period of 112 days. Early in the experiment only minor differences in population density between the various colicin-producing and the non-producing control strains were detected. However, over time, the density of the control strains plummeted, while that of the colicin-producing strains remained significantly higher (F_(7,66) = 2.317; P < 0.0008). Conclusion: The data presented here support prior claims that bacteriocin production may play a significant role in the colonization of E. coli in the gastrointestinal tract. Further, this study suggests that the ability to produce bacteriocins may prove to be a critical factor in determining the success of establishing probiotic E. coli in the gastrointestinal tract of humans and animals.

Premise: Intraspecific variation in diaspore characteristics could affect various aspects of plant performance at the population, individual plant, and seed levels. We quantified variation in dispersal traits in a wind‐dispersed annual, Geropogon hybridus (Asteraceae), focusing on continuous morphological traits of dispersive diaspores and their relationships to dispersal ability and seedling emergence.Methods: We measured the morphological traits, terminal velocity, and seedling emergence of 1140 seeds from 10 populations in two successive years. We assessed the variation in traits among three hierarchical levels of organization and between years, and quantified their effects on diaspore terminal velocity and seedling emergence.Results: Diaspore morphological traits varied substantially at the population, plant, and diaspore levels. Variables of pappus geometry, especially pappus width and pappus opening angle, were consistent between years and were found to be the best predictors of diaspore terminal velocity and seedling emergence. There was a significant negative relationship between diaspore terminal velocity and seedling emergence.Conclusions: The intraspecific variation in diaspore traits is sufficiently large to substantially allow a dispersal–dormancy trade‐off of individual diaspores. Our results support the hypothesis that traits of dispersive diaspores evolve in concert to select for increased dispersal potential, and provide an avenue to predict plant offspring performance through simply measured traits.