Jawad Sakarchi , Rachel Germain

Recent developments in competition theory, namely, Modern Coexistence Theory (MCT), have aided empiricists in formulating tests of species persistence, coexistence, and evolution from simple to complex community settings. However, the parameters used to predict competitive outcomes, such as interaction coefficients, invasion growth rates, or stabilizing differences, remain biologically opaque, making findings difficult to generalize across ecological settings. Here, our article is structured around five goals, towards clarifying MCT by first making a case for the modern-day utility of MacArthur’s consumer-resource model, a model with surprising complexity and depth: (i) to describe the model in uniquely accessible language, deciphering the mathematics towards cultivating deeper biological intuition about competition’s innerworkings regardless of what empirical toolkit one uses, (ii) to provide translation between biological mechanisms from MacArthur’s model and parameters used to predict coexistence in MCT, (iii) to make explicit important but understated assumptions of MacArthur’s model in plain terms, (iv) provide empirical recommendations, and (v) to examine how key ecological concepts (e.g., r/K selection) can be understood with renewed clarity through MacArthur’s lens. We end by highlighting opportunities to explore mechanisms in tandem with MCT and to compare and translate results across ecological currencies towards a more unified ecological science.