Reduced foraging investment as an adaptation to patchy food sources: a phasic army ant simulation

3 Abstract 4 Colonies of several ant species within the subfamily Dorylinae alternate 5 stereotypical discrete phases of foraging and reproduction. Such phasic cycles are 6 thought to be adaptive because they minimize the amount of foraging and the related 7 costs, and at the same time enhance the colony-level ability to rely on patchily 8 distributed food sources. In order to investigate these hypotheses, we use here a 9 simple computational approach to study the population dynamics of two species of 10 virtual ant colonies that differ quantitatively in their foraging investment. One species, 11 which we refer to as “phasic”, forages only half of the time, mirroring the phasic 12 activity of some army ants; the other “non-phasic” species forages instead all the 13 time. We show that, when foraging costs are relatively high, populations of phasic 14 colonies grow on average faster than non-phasic populations, outcompeting them in 15 mixed populations. Interestingly, such tendency becomes more consistent as food 16 becomes more difficult to find but locally abundant. According to our results, reducing 17 the foraging investment, for example by adopting a phasic lifestyle, can result in a 18 reproductive advantage, but only in specific conditions. We thus suggest phasic 19 colony cycles to have emerged together with the doryline specialization in feeding on 20 the brood of other eusocial insects, a resource that is hard to obtain but highly 21 abundant if available. 22