Data from: 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 described
by the model, supporting the notion that body size changes to match bodily
demand for resources with the available supply of resources. Surprisingly,
despite the 10-fold variation in Didinium body size, we found that static
model parameters were sufficient to describe the data, suggesting a lack
of eco-evolutionary dynamics. 4. A pressing need in ecology is to be able
predict changes in body size under novel scenarios, especially climate
warming. The dynamic SD model does this by linking body size to the
ecological context in an eco-evolutionary framework. Our approach expands
our ability to understand rapid linked changes in traits and abundance.