Stochastic variation in food availability influences weight and age at maturity

Variation in mean food availability, and in the variance around the mean, a ffects the growth rate during development. Previous theoretical work on the influence of environmental quality or growth rates on the phenotypic trait s age and size at maturation assumed that there is no variation in growth r ate or food availability within a generation. We develop a stochastic dynam ic programming (SDP) model of the foraging behaviour of aphidophagous syrph ids, and use this model to predict when syrphids should pupate (mature) whe n average food availability changes, or varies stochastically, during devel opment. The optimal strategy takes into account not only the availability of food, but also the timing of its availability. Food availability, when small, inf luences developmental time, but not weight at pupation. Food availability, when large, influences weight at pupation, but not developmental time. When the food supply is low, the optimal strategy adjusts the size at pupation downwards for stochastic as opposed to deterministic availability of food. The conclusions reinforce the need for life-history studies to consider sta te dependence and short-term variability in growth rates. (C) 2000 Academic Press.