The ecology and evolution of collective behavior

Ant colonies operate without central control, using feedback from simple olfactory interactions to regulate their activities. There are more than 14K species of ants in every habitat on Earth, using diverse stochastic algorithms, producing different feedback regimes, in different environments. These algorithms have evolved to fit the dynamics of particular environments, including energy flow, stability, and the threat of rupture. Harvester ants in the harsh but stable conditions of the desert, regulate foraging effort according to current food availability and humidity, using excitable dynamics based on the rate of contact inside the nest between returning and outgong foragers. The feedback system sets a default of inactivity unless conditions are favorable. For turtle ants in the trees of the tropical forest, high humidity makes activity easy but competition is high. Their trail networks are constrained to follow the nework of vegetation. They use the rate of deposition of a volatile pheromone to build and maintain a distributed routing network in heterogeneous environments, based on design principles that differ from the shortest paths commonly studied in ants and in network science. The feedback system sets a default of persistent activity unless conditions are unfavorable. The diversity of ants provides opportunities to learn how collective behavior evolves to fit diverse environmental dynamics.