Figure 1.Clarifying confusion about differences between attack rates, consumption rates, and utilization (A–D). A and C depict the attack rate functions of two consumers, red (consumer i) and blue (consumer j), where A shows how resource abundance determines how many resources are consumed by each species at any moment in time (B) while C shows how resource exploitability determines how resources are consumed by each species at resource equilibrium (D; determining utilization rates; see “Utilization Functions”). E shows an underpacked community where some resources are underutilized, leaving the community susceptible to invasion, whereas F presents a community of species that fully utilize available resource production and thus are fully “packed.” The gap in gray between Rk and the summed utilization functions represents the 𝒰 component of 𝒬 (see “Community Utilization”).
Abstract
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, and stabilizing differences, remain biologically opaque, making findings difficult to generalize across ecological settings. This article is structured around five goals toward 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 toward cultivating deeper biological intuition about competition’s inner workings 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) to 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 toward a more unified ecological science.