Tradeoffs have long been an essential part of the canon explaining the maintenance of species diversity. Despite the intuitive appeal of the idea that no species can be a master of all trades, there has been a scarcity of linked demographic and physiological evidence to support the role of resource use tradeoffs in natural systems. Using five species of Chihuahuan desert summer annual plants, I show that demographic tradeoffs driven by short-term soil moisture variation act as a mechanism to allow multiple species to partition a limiting resource. Specifically, by achieving highest fitness in either rainfall pulse or interpulse periods, variability reduces fitness differences through time that could promote coexistence on a limiting resource. Differences in fitness are explained in part by the response of photosynthesis to changing soil moisture. My results suggest that increasing weather variability, as predicted under climate change, could increase the opportunity for coexistence in this community.