How to quantify competitive ability

1. Understanding the role of competition in structuring communities requires that we quantify competitive ability in a way that permits us to predict the outcome of competition over the long term. Given such a clear goal for a process that has been the focus of ecological research for decades, there is surprisingly little consensus on how to measure competitive ability, with up to 50 different metrics currently proposed. 2. Using competitive population dynamics as a foundation, we define competitive ability-the ability of one species to exclude another-using quantitative theoretical models of population dynamics to isolate the key parameters that are known to predict competitive outcomes. 3. Based on the definition of competitive ability we identify the empirical requirements and describe straightforward methods for quantifying competitive ability in future empirical studies. In doing so, our analysis also allows us to identify why many existing approaches to studying competition are unsuitable for quantifying competitive ability. 4. Synthesis. Competitive ability is precisely defined starting from models of competitive population dynamics. Quantifying competitive ability in a theoretically justified manner is straightforward using experimental designs readily applied to studies of competition in the laboratory and field.