Eco-evolutionary Dynamics at High Diversity*

Much of our understanding of ecological and evolutionary mechanisms derives from analysis of low-dimensional models: with few interacting species, or few axes defining “fitness”. It is not always clear to what extent the intuition derived from low-dimensional models applies to the complex, high-dimensional reality. For instance, most naturally occurring microbial communities harbor a strikingly large number of coexisting species, and understanding the eco-evolutionary interplay in these systems is an exciting new domain for statistical physics. Recent work demonstrated that the high-diversity limit of classic consumer-resource models is analytically tractable, offering a promising new platform for investigating ecology in this regime. Here, we describe how the same analytical framework can be extended to also study evolutionary questions. Our analysis shows how, at high dimension, the intuition promoted by a one-dimensional (scalar) notion of fitness can become misleading. Specifically, while the low-dimensional picture emphasizes organism cost or efficiency, we exhibit a regime where cost becomes irrelevant for survival, and link this observation to properties of high-dimensional geometry as manifested in our model.