FORUM Resource competition and plant traits : a response to Craine et al . 2005

1 Resource competition theory incorporates the mechanisms that underlie consumer– resource interactions and the trade-offs that constrain these mechanisms. Contrary to assertions by Craine, the concept of R* as the measure of resource reduction and the predictor of resource competition has not changed since it was proposed more than two decades ago. 2 Resource reduction, as summarized in R*, is readily observed. Soil concentrations of nitrate and water are decreased by plant uptake, and are lowered to different levels by different species. Tests have shown R* theory to correctly predict competitive outcomes for a variety of organisms and ecosystems. 3 Consumer-resource mechanisms are a building block for theories that incorporate other trade-offs faced by plants, such as those between competitive ability and dispersal. 4 Numerous plant traits interactively determine R* in a manner predictable from traitbased resource competition theory. The same traits shown by comparative research to be associated with plant dominance in low-nutrient habitats give lower R* values, greater predicted competitive ability and greater predicted abundances in nutrientlimited habitats. 5 Plant ecology needs closer links between analytical theory, observations and experiments. Simple verbal theories can generate novel ideas but the logical implications of such scenarios are best explored using the rigorous logic of mathematics. Predictions of theory can then be tested via experiments and comparative studies.