Individual versus collective decision making: optimal foraging in the group-hunting termite specialist Megaponera analis

Abstract

Collective decision making is one of the main mechanisms of organization in social insects. However, individual decision making can also play an important role, depending on the type of foraging behaviour. In the termite-hunting ant species Megaponera analis information about foraging sites is collected by only a handful of individual scouts that have to convey this information to the colony as accurately as possible to optimize their foraging behaviour. We therefore looked at predictions made by optimal foraging theory to better understand the interplay between collective and individual decision making in this obligate group-raiding predator. We found a clear positive relation between raid size (200–500 ants) and termite abundance at the foraging site thereby confirming predictions of the maximization of energy theory. Furthermore, selectivity of the food source increased with distance, thus confirming central place prediction theory. The confirmation of these theories suggests that individual scouts must be the main driver behind raid size, choice and raiding behaviour. The marginal value theorem was also confirmed by our results: time spent at the hunting ground increased with distance and prey quantity. This raises questions on how foraging time at the food source is regulated in a group-hunting predator. Hunger decreased selectivity of scouts with respect to food sources, while average raid size increased and more scouts left the nest in search of prey, thus implying that scouts are aware of the hunger state of the colony and adapt their decision making accordingly. Remarkably, most central place foraging behaviours in M. analis were not achieved by collective decisions but rather by individual decisions of scout ants. Thus, 1% of the colony (10–20 scouts) decided the fate and foraging efficiency of the remaining 99%.