Competition is commonly thought to drive character divergence by increasing the fitness of individuals who differ in resource use from their competitors.  However, when resources are not nutritionally-substitutable, or when the cost of substituting resources is high, competition may drive evolutionary convergence in resource use traits.  Using an adaptive dynamics model we explore the conditions under which competitors exhibit character convergence (and alternatively divergence) in a 2-consumer, 2-resource model where i) both resources are required in the diets of the consumer (non-substitutable resources) and ii) consumers benefit from a mixed diet (partially-substitutable resources). 

Results/Conclusions

By comparing the optimal resource use traits of competitors in allopatry to those in sympatry we find that character convergence always occurs when resources are non-substitutable; however when resources are partially-substitutable, character convergence only occurs when the benefit of a mixed diet is relatively high.  The combination of neutrally-stable ecological dynamics and stable adaptive dynamics in these models generates surprising dynamics including transient near-extinction, transient reversals in the direction of trait evolution, and reactivity to density perturbations.