Predator-prey dynamics and the plasticity of predator body size

1. Body size is of fundamental importance to the structure and function of natural systems, yet the factors selecting for certain body sizes are still not well understood. Resource supply levels clearly play a role in setting size, but in current theory, optimality functions for body size are not tied to the population dynamics that govern resource supply, minimizing our ability to understand how body size evolves in response to ecological context. 2. We integrated the supply-demand (SD) model of body size evolution with a model of predator-prey dynamics to create a dynamic SD model that describes predator body size variation through time. We tested the model with experimental data on body size and abundance dynamics in the Didinium-Paramecium predator-prey system. We used a new differential equation fitting approach along with independently estimated parameters to determine whether the model could simultaneously capture both abundance and body size dynamics. 3. The dynamics were well d...