Before revision:  Here, we use a mathematical model describing the dynamics of resources, toxins, and microbial species in a chemostat where resource supplies switch. Over most of the explored parameter space, speciescompeted, but the strength of competition peaked at either low, high  or intermediate switching rates depending on the species' sensitivity to toxins.
After revision:  Here, we use a mathematical model describing two microbial species living in an environment where substrate supplies randomly switch between abundant and scarce. We then vary the rate of switching as well as different properties of the interacting species, and measure the probability of the weaker species driving the stronger one extinct. We find that this probability increases with the strength of demographic noise, and peaks at either low, high or intermediate switching rates depending on the species' sensitivity to toxins.