Tilman’s R* theory set forth over 35 years ago still shapes the way ecologists think about resource competition. When a consumer requires two essential resources, the evolutionarily stable strategy is to reach a point of co-limitation. That is, a point at which neither resource is being taken up in excess. When two consumers compete for the same essential resources, we can use this idea of co-limitation to understand when we should expect stable coexistence, priority effects, or competitive exclusion. These models provide insights that others cannot because they incorporate a specific mechanism of how competition occurs. However, one critical feature of competition remains unaccounted for in such models – intraspecific variation. Here, we present an ecological model based on the Tilman competition framework for both one and two consumer species on two essential resources. We model a trait distribution that maps onto the uptake of resources via a steep sigmoidal function. We investigate the role of intraspecific variation on coexistence in the absence and presence of phenotypic change.
Results/Conclusions
We find in the one consumer species case that intraspecific variation changes the evolutionary stable strategy and, unlike other classes of resource competition, phenotypic variation optimizes population fitness at an intermediate value. In the two species case, we find that an intermediate amount of intraspecific variation promotes coexistence between consumers. Here, intraspecific variation leads to a strengthening of intraspecific competition relative to interspecific competition through non-linear effects on resource abundance that enhance niche differences and equalize fitness differences. Our model is the first ecological model with biologically realistic assumptions that explores how intraspecific trait variation affects resource competition and coexistence.