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Recruitment and entropy decrease during trail formation by foraging ants

Abstract

Social insects utilise a complex spatial orientation system mediated by chemical signals. This study investigated how the foraging behaviour of ants (Dorymyrmex thoracicus) varies depending on the quantity of an available resource using a field experiment. Further, we demonstrated computationally that ant displacement is compatible with a model based on pheromone deposition. Our experiment tested how the resource size (large or small) and availability (one or two simultaneous patches) of resources offered influence the number of recruited ants (traffic flow) and the speed of traffic flow both moving towards a resource and returning to the colony. The results showed that the returning flow was higher than the going flow independent of resource. The traffic flow towards a single resource was higher than the flow for either of two simultaneous resources patches offered; thus, multiple resources sources split the flow, regardless of the fact that resource size did not affect foraging choices. Our results indicated that the ants used an orientation mechanism that can be reproduced by a theoretical computer model. With our model, we showed that initially, the displacement of ants followed no clearly detectable pattern. However, with increasing levels of ant recruitment and consequent pheromone deposition on the most used trails, returning displacement revealed the formation of shorter and more organised trails. The model revealed key transition between periods of order and disorder that continued until the flow of information reached an organised state (Shannon entropy). This study highlights an exceptional mechanism of foraging optimisation in eusocial insects.

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Acknowledgements

The authors thank the Postgraduate Programs in Ecologia de Biomas Tropicais of Universidade Federal de Ouro Preto and in Biodiversidade e Uso dos Recusos Naturais of Universidade Estadual de Montes Claros for organising the field course in 2012 and provide logistical support. We gratefully acknowledge the staff of the Reserva Natural Vale for allowing us to work in the reserve. We thank the researcher Fabiana Cuezzo for the identification of the species Dorymyrmex thoracicus, and researcher Reisla Oliveira for photographing the field activities. This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior—Brasil (CAPES)—Finance Code 001. GML thanks for a research scholarship from Conselho Nacional de Desenvolvimento Científico e Tecnológico—CNPq (155895/2014-1) and CAPES (88881.133074/2016-01). FK thanks for a research scholarship from CNPq (140647/2018-0). RF is granted by the CNPq. PL has a student fellowship (CVU 771366 from the Consejo Nacional de Ciencia y Tecnología (CONACYT), Mexico. SPR is granted by the CNPq (304024/2015-5). EA is granted by the CAPES (2657-12-0) and CNPq (425333/2018-3).

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Correspondence to G. M. Lourenço.

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Lourenço, G.M., Keesen, F., Fagundes, R. et al. Recruitment and entropy decrease during trail formation by foraging ants. Insect. Soc. 67, 59–69 (2020). https://doi.org/10.1007/s00040-019-00728-6

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  • DOI: https://doi.org/10.1007/s00040-019-00728-6

Keywords

  • Atlantic forest
  • Computer model
  • Dorymyrmex thoracicus
  • Entropy