To grow or to reproduce? The role of life-history plasticity in food web dynamics

The size of an individual is a key feature influencing and determined by a species' life history and ecology. Here, I consider how life-history plasti city within a single species can influence the outcome of food web interact ions along a productivity gradient. An individual can either reproduce earl y but remain susceptible to predators throughout its life (strategy 1) or d elay reproduction and grow to a predator-invulnerable size refuge (strategy 2). At low productivity, strategy 1 is favored because the probability of growing to a size refuge is low compared to the probability of being eaten. Here, the system is consumer controlled, and predators have large effects on the food web. At high productivity, strategy 2 is favored because high f ood availability increases the probability of prey attaining size refuge be fore being eaten. Consequently, the system becomes less consumer controlled , and predators have weaker effects on food web dynamics. At intermediate p roductivity, either strategy 1 or strategy 2 can be favored, depending on t he initial conditions of the system. Field and laboratory experiments with a common freshwater snail Helisoma trivolis and its insect predator Belosto ma flumineum support both the key assumptions and predictions of the models .