Revisiting the R* theory: Pre-emption competition allows coexistence on a single limiting resource

Background/Question/Methods: Understanding the consequences of competition among organisms is a long-standing goal in ecology. The R* model is the most common approach for investigating resource competition. This model predicts that the species with the most efficient resource use (lowest R*) will exclude all other species when there is one limiting resource. Another prediction is that species extinction due to resource limitation can only result from competition (species cannot become extinct when there are no competitors). The R* model is widely used despite its many unrealistic assumptions because alternative models are much more complex and system specific. Here, we propose a simple and analytically tractable model that relaxes the assumption that all species acquire the same (per capita) amount of resource. Instead, it assumes that some species are able to pre-empt the resource before their competitors. Later, we use a simulation-based approach for incorporating the discrete nature of individuals into this new model.

Results/Conclusions: The analytical model predicts that the most dominant species is not necessarily the most efficient one. Furthermore, this model produces coexistence of many species when there is a trade-off between efficiency and pre-emption ability. In addition, result of the simulation model show that extinction could be independent of competition under low resource availability. Altogether our models unify many organism-specific models and trade-offs into a one general trade-off between pre-emption and efficiently which is probably the main coexistence mechanism under resource competition.