Department of Collective Behaviour, Max Planck Institute of Animal Behavior, Konstanz D-78457, Germany;
Centre for the Advanced Study of Collective Behaviour, University of Konstanz, Konstanz D-78457, Germany.
Proc Natl Acad Sci U S A. 2021 Apr 27;118(17). doi: 10.1073/pnas.2013741118.
An inherent strength of evolved collective systems is their ability to rapidly adapt to dynamic environmental conditions, offering resilience in the face of disruption. This is thought to arise when individual sensory inputs are filtered through local interactions, producing an adaptive response at the group level. To understand how simple rules encoded at the individual level can lead to the emergence of robust group-level (or distributed) control, we examined structures we call "scaffolds," self-assembled by army ants on inclined surfaces that aid travel during foraging and migration. We conducted field experiments with wild colonies, manipulating the slope over which ants traversed, to examine the formation of scaffolds and their effects on foraging traffic. Our results show that scaffolds regularly form on inclined surfaces and that they reduce losses of foragers and prey, by reducing slipping and/or falling of ants, thus facilitating traffic flow. We describe the relative effects of environmental geometry and traffic on their growth and present a theoretical model to examine how the individual behaviors underlying scaffold formation drive group-level effects. Our model describes scaffold growth as a control response at the collective level that can emerge from individual error correction, requiring no complex communication among ants. We show that this model captures the dynamics observed in our experiments and is able to predict the growth-and final size-of scaffolds, and we show how the analytical solution allows for estimation of these dynamics.
进化的集体系统的一个固有优势是它们能够快速适应动态环境条件，在面对破坏时具有弹性。这被认为是当个体感觉输入通过局部相互作用进行过滤时，在群体水平上产生适应性反应时出现的。为了了解简单规则如何在个体水平上编码，从而导致强大的群体水平（或分布式）控制的出现，我们研究了被称为“支架”的结构，这些结构是由行军蚁在倾斜表面上自组装而成的，有助于在觅食和迁徙过程中行进。我们对野生群体进行了野外实验，通过操纵蚂蚁穿越的坡度来检查支架的形成及其对觅食交通的影响。我们的结果表明，支架经常在倾斜表面上形成，并且它们通过减少蚂蚁的滑倒和/或掉落来减少觅食者和猎物的损失，从而促进了交通流量。我们描述了环境几何形状和交通对它们生长的相对影响，并提出了一个理论模型来研究支架形成的个体行为如何驱动群体水平的效应。我们的模型将支架的生长描述为集体水平的控制反应，它可以从个体纠错中产生，而不需要蚂蚁之间的复杂通信。我们表明，该模型捕获了我们实验中观察到的动态，并且能够预测支架的生长和最终大小，我们还展示了分析解如何允许对这些动态进行估计。
