Thursday, 3 August 2006
542

A Density-Dependent Phase Transition in Colony Foraging Efficiency and Individual Flexibility in Honey Bees

Andreas Loengarov and Valery Tereshko. School of Computing, University of Paisley, Paisley, PA1 2BE, United Kingdom

When biological units are integrated into a whole such as a social insect colony, it is sometimes found that the complexity of behavior at the unit level is lowered as behavioral complexity increases at the colony level (either on an evolutionary or a developmental scale). Moreover, such a transition sometimes happens not smoothly, but quite suddenly when a certain parameter treshold is crossed. This may be called a phase transition. For instance, division of labour on the colony level may appear in this way when colony population density is increased beyond a certain treshold, for instance in nest building in certain wasps (Karsai & Wenzel 1998. Proc. Nat. Acad. Sci. 95: 8665-8669). Beekman et al. (2001. Proc. Nat. Acad. Sci. 98: 9703-9706) showed that for Pharaoh's ants, Monomorium pharaonis, a phase transition exists for the proportion of ants involved in foraging, depending on colony size. When colony size increases beyond a treshold, foraging switches phase from disordered foraging to ordered foraging that makes use of pheromone trails. We have modeled a similar phenomenon for the honey bee, Apis mellifera, using a minimal ordinary differential equation model based on current knowledge of A. mellifera foraging. Honey bees use a recruiting mechanism quite different from that of ants; even so, a sharp phase transition from disordered (scouting-based) to ordered (recruitment dance-based) foraging is found here as well, with an intermediary bistable phase. Although not easy to operationalize, individual behavioral complexity, flexibility, or choice can be considered greater for a scouting bee than for a recruited bee. Thus, in the ordered phase individual complexity and flexibility are sacrificed for colony efficiency.


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