Enhanced Biodiversity in Time-dependent Environments

Natural ecosystems, in particular on the microbial scale, are typically inhabited by a large number of species. In contrast, purely competitive nonlinear population dynamics models in general predict only one surviving species (competitive exclusion principle). In these models, the environmental parameters, such as the resource abundance, are often assumed to be constant. Thus, the impact of a time-dependent environment on the ecosystem biodiversity is not captured by such models. In nature, however, most environments are in fact changing periodically, such as the mammalian gut microbiome in response to the circadian rhythm. Here, we show that including a periodic time dependence in a generic population dynamics model can enhance the biodiversity of the system. We demonstrate that, in general, nonlinear interactions between species combined with a temporally varying environment can enhance biodiversity in the class of competing species models. Our results offer a mechanism to explain how biodiversity and genetic variation could have been maintained in various systems, ranging from mammalian gut microbiota to early Earth environments.