Fight or flight: plastic behavior under self-generated heterogeneity

Plants are able to plastically respond to their ubiquitously heterogeneous environments; however, little is known about the conditions under which plants are expected to avoid or confront their neighbors in dense stands, where heterogeneity is self-generated by non-uniform growth and feedback between plant interactions and stand heterogeneity. We studied the role of plasticity for spatial pattern-formation and the resulting stand-level fitness of clonal plants, assuming variable types of plastic behavior. Specifically, the adaptive values of behavior ranging from pure avoidance, to neutral and pure confrontation were assessed using a simulation model of stands of clonally growing plants with varying capacity of plastic behavior. The results demonstrated significant effects of the type of competitive behavior on mean final densities of single-species stands at equilibrium. Density was the lowest and aggregation was the highest in stands of purely confrontational plants, and density was highest in stands of neutral and purely avoiding plants. When competing against a neutral photometer (i.e. non-plastic but otherwise identical plant), the best competitors were plants that avoided their neighbors in 0.33–0.50 of the cases and were neutral otherwise. Differences in adaptive values of individual behaviors depended both on the distance over which the environmental structure (i.e. local density) was perceived, and on overall density. Density-independent ramet mortality profoundly changed the effectiveness of competitive behaviors. Under high levels of mortality, avoidance was the most effective and confrontation the least effective behavior. The results indicate that individual-based behaviors might affect higher organizational levels, and that their reciprocal interactions with resource levels and patchiness, and responsiveness to density-independent mortality might generate higher-order feedbacks that intricately affect the fate of individual ramets and the patterning of whole stands and communities.