Pulsed-resource dynamics constrain the evolution of predator-prey interactions.

Although temporal variability in the physical environment plays a major role in population fluctuations, little is known about how it drives the ecological and evolutionary dynamics of species interactions. We studied experimentally how extrinsic resource pulses affect evolutionary and ecological dynamics between the prey bacterium Serratia marcescens and the predatory protozoan Tetrahymena thermophila. Predation increased the frequency of defensive, nonpigmented prey types, which bore competitive costs in terms of reduced maximum growth rate, most in a constant-resource environment. Furthermore, the predator densities of the pulsed-resource environment regularly fluctuated above and below the mean predator densities of the constant environment. These results suggest that selection favored fast-growing competitor prey types over defensive but slower-growing prey types more often in the pulsed-resource environment (abundance of resources and low predation risk). As a result, the selection for prey defense fluctuated more in the pulsed-resource environment, leading to a weaker mean response in prey defense. At the ecological level, the evolution of prey defense weakened the relative strength of top-down regulation on prey community. This was more evident in the constant-resource environment, whereas the slow emergence of defensive prey types gradually decreased the amplitude of predator peaks in the pulsed-resource environment. Our study suggests that rapid evolution plays a smaller role in the ecological dynamics of communities dominated by resource pulses.