We have previously modeled resource competition between plants of different sizes, that interact with their environment at different scales. Those models show that size-based differences in how competitors affect and respond to resource concentrations generate both costs and benefits to large size as a trait, and promote local coexistence of competitors of different sizes. Resource recycling, not included in the earlier models, may also be important for the implications of size asymmetries, since large competitors growing across multiple patches might effectively transport resources between those patches via their litter. Here, we introduce resource recycling into a model where competitors differ in the scale at which they perceive their environment.
Results/Conclusions
In a two-resource, two-patch system with both external inputs and recycling, larger species often generate resource distributions that favor their smaller competitors, and vice-versa. This occurs because the larger competitor's litter, which is deposited uniformly across patches, transports resources from areas of high concentration to areas of low concentration. This reduces the patch heterogeneity and complementarity that tend to favor the large species. The smaller competitor does not cause any cross-patch transport, and so heterogeneity and complementarity are restored when that species is abundant. Together, recycling and external inputs allow coexistence when it is not possible with either alone. Damped oscillations can be generated, where each species increases while its competitor is decreasing. With recycling, presence of the large species can also facilitate higher biomass of its smaller competitor than would have occurred otherwise. This can also occur in a one-resource system, due to nonlinear averaging. The negative feedback between competitors predicted here is opposite what is expected based on earlier models focused on litter chemistry. There, production of recalcitrant litter by species with lower resource requirements and production of highly decomposable litter by species with high resource requirements is expected to generate positive feedback between competitors. Our model suggests that size asymmetries between competitors can alter the implications of litter recycling in a system, and, reciprocally, that the degree of recycling can mediate the effects of such size asymmetries.
