Two's More Fun than One: How the Presence of Multiple Nutrients Changes Microbial Competition and Foraging in Unexpected Ways

Abstract

Microbes exist in incredibly diverse environments with many possible resources (i.e. nutrients) to compete and forage for. To make this complex system tractable, ecologists often study microbes in the presence of a single resource in order to predict and explain what happens with multiple resources. But what gets lost when we do this? Are there phenomena that only emerge in the presence of multiple resources? Here, I explore the ecological implications of three phenomena that each require the presence of at least two resources. First, I show that the diauxic lags that occur when a microbe needs to switch between resources after one is depleted can allow ‘fast-switcher’ microbes to coexist with competitors that exclude them in single-resource environments. Then, I derive a rich temporal niche structure that arises from variations in the order in which resources are depleted in ecosystems with a pulsed resource supply and show that these temporal niches reshape community structure, vastly increasing the expected diversity of microbial ecosystems. Finally, I present a novel differential strategy in which a microbe attempting to intercept a moving source of multiple resources can treat one resource as an attractant and the other as a repellent to significantly increase its chances of successfully intercepting the source as compared to just being attracted to the resources released by the source. Each of these phenomena fundamentally requires the presence of at least two resources and reshapes microbial behavior and ecology. Thus, they collectively highlight the need to carefully consider how characterizations from single-resource environments actually combine to determine what happens in multi-resource environments and what new dynamics must be accounting for in such a bottom-up approach. I conclude with an argument that the case of two resources may be particularly relevant to study due to how much complexity can emerge at just the first step up from one resource to two.