Ecological stoichiometry and the shape of resource-based tradeoffs

Fitness tradeoffs are expected when organisms must allocate a limited resource between two or more traits. Despite the fact that most resources are made up of multiple elements or components, tradeoff models have traditionally been implicitly or explicitly based on a single currency. Here I propose a model for a resource-based tradeoff between two traits that share two resource elements, and suggest ecological stoichiometry as a critical mechanism controlling the shape of tradeoffs. The tradeoff curve in the model has different shapes depending on the elemental stoichiometry of the traits and the available resource. I further describe a conceptual framework that combines a tradeoff curve with a fitness function to predict an optimal combination of traits in stoichiometrically different environments. The model suggests that even though the fitness function is fixed, an optimal combination of traits can vary depending on the stoichiometry of both the traits and the supplied resource.