Weak support for ergodic processes in structuring Pleistocene mammal communities in western Europe

The idea that space and time act equivalently in structuring ecological communities has historically been predicted based on qualitative observations. The space–time equivalence hypothesis can be stated in terms of ergodicity: that system averages over space and time are equivalent. We explicitly examine ergodicity in the fossil mammal community structures of western Europe’s middle and Late Pleistocene, focusing on warm periods (corresponding to odd Marine Isotope Stages). Support for ergodicity is present in rich guilds but absent in the most sparsely occupied guilds. Absence of ergodicity can be attributed to chaotic responses to climate cycles over the study region, which have previously shown to violate traditional community convergence models. We suggest that these responses disproportionately disrupted sparsely occupied guilds, leading to non-ergodic dynamics controlling their assembly. Ergodicity may be better established across glacial refuges, at finer temporal scales, or across more climatically stable geographic regions.