Coarse-graining ecological dynamics in the face of unkown microscopic details

Any description of microbial communities necessarily ignores some details of the underlying diversity. What predictions can be robust to such omissions and coarse-grained descriptions? Here, building on the theoretical framework of resource competition, we introduce an eco-evolutionary model that allows organisms to be described at an arbitrary level of detail, enabling us to formally study the hierarchy of possible coarse-grained descriptions. Within this model, we demonstrate that the ability of coarse-graining schemes to appropriately describe a community depends on the quantity we aim to predict (e.g., invasion rates versus strain abundances). We further show that robustness of predictions to coarse-graining requires two conditions: the ecological context in which we test a coarse-grained prediction must remain highly diverse, and this diversity must be derived from a sufficiently similar environment as the one used for testing. We use our model to argue that studying communities away from their natural eco-evolutionary context may eliminate the very reasons that make a coarse-grained description an adequate characterization of the natural diversity.