Emergent properties of food distribution among fire ant larvae

The flow of food into a fire ant colony is a decentralized process in which a global pattern, the even distribution of food among larvae, emerges from the interactions of individuals responding to each other with relatively simple rules of thumb. A simulation of worker-larva feeding interactions (rate and duration of worker-to-larva regurgitation) was employed to resolve the effect of each behavioral component on the distribution of food among larvae during one meal. When feeding interactions between workers and larvae simulated those of the fire ant (larvae signal for feedings at rates depending upon their size and their level of hunger; workers regurgitate a small, fixed volume of food), meal size was proportional to larval size, all larvae were brought to fullness together over an eight-hour period and the proportion of protein in each larva's meal was proportional to that found in the environment. These patterns of food distribution among larvae were the standard against which we compared simulated interactions. When simulated larvae signaled for feedings based upon their hunger (percent of midgut emptiness) but not their size, workers required nearly 12 hours to fill the last larva and, some larvae became full far sooner than others. When simulated larvae signaled for feedings based upon their size but not their hunger, they were brought to fullness evenly over time but were grossly overfed, absorbing food that would have been stored in worker crops. Lengthening the duration of worker-to-larva regurgitation generated substantial variation in the proportion of protein in larval meals, especially among small larvae. When simulated interactions were randomized, larvae received meals that varied substantially in volume and protein, some larvae were filled far sooner than others, and workers required over 24 hours and twice as much food to bring the last larva to fullness. Variation in worker response thresholds (simulated as variable worker-larvae ratios) affected only the total time required to deliver meals to larvae, Dissecting the relationship between worker-larva feeding interactions and the distribution of protein among larvae allowed us to propose a mechanism by which colony growth and reproduction could be regulated. Copyright 1998 Academic Press