Growth-density inversion in Escherichia coli reveals superlinear, not sublinear, and density dependence

Density dependence is a core principle in ecology and evolution, and yet the shape of the relationship between per capita growth and population size remains contentious. Sublinear (decelerating) density dependence has been widely reported in empirical studies, but the apparent ubiquity of sublinearity is at odds with resource competition theory. Moreover, most estimates of density dependence suffer from underappreciated statistical biases and weak inference. Using a microbial, continuous-culture approach that bypasses the limitations of conventional methods by inverting the direction of causality, we report robust evidence for superlinear (accelerating) density dependence, in agreement with theory. These results underscore the need for concerted efforts to reconcile a widening disconnect between mechanistic and phenomenological approaches to inference on the shape of density dependence. Resolving this debate has wide implications for past and future research into species coexistence and ecosystem stability, and in conservation and natural resource modelling.