Direction matching for sparse movement data sets: determining interaction rules in social groups

It is generally assumed that high-resolution movement data are needed to extract meaningful decision-making patterns of animals on the move. Here we propose a modified version of force matching (referred to here as direction matching), whereby sparse movement data (i.e., collected over minutes instead of seconds) can be used to test hypothesized forces acting on a focal animal based on their ability to explain observed movement. We first test the direction matching approach using simulated data from an agent-based model, and then go on to apply it to a sparse movement data set collected on a troop of baboons in the DeHoop Nature Reserve, South Africa. We use the baboon data set to test the hypothesis that an individual’s motion is influenced by the group as a whole or, alternatively, whether it is influenced by the location of specific individuals within the group. Our data provide support for both hypotheses, with stronger support for the latter. The focal animal showed consistent patterns of movement toward particular individuals when distance from these individuals increased beyond 5.6 m. Although the focal animal was also sensitive to the group movement on those occasions when the group as a whole was highly clustered, these conditions of isolation occurred infrequently. We suggest that specific social interactions may thus drive overall group cohesion. The results of the direction matching approach suggest that relatively sparse data, with low technical and economic costs, can be used to test between hypotheses on the factors driving movement decisions.

学界普遍认为，若要提取动物移动过程中的有意义决策模式，需获取高分辨率运动数据。本文提出一种改进版的力匹配（force matching）方法，本文中将其称为方向匹配（direction matching）；该方法可利用稀疏运动数据——即采集间隔以分钟而非秒为单位的数据——来检验作用于目标动物（focal animal）的受力假说，基于假说力能否解释观测到的运动行为以验证假说合理性。我们首先基于智能体模型（agent-based model）生成的模拟数据，对方向匹配方法开展验证；随后将该方法应用于南非DeHoop自然保护区内采集的一群狒狒的稀疏运动数据集。我们利用该狒狒数据集检验两项对立假说：其一为个体运动受整个群体的影响，其二为个体运动受群体内特定个体的位置所调控。我们的数据为两项假说均提供了支持，且对后者的支持力度更强。当目标个体与特定个体的距离超过5.6米时，其移动会呈现出朝向该个体的一致性模式。尽管当整体群体高度聚集时，目标个体也会对群体运动产生响应，但这类高度聚集的场景发生频率较低。据此我们推测，特定的社会互动或许是推动群体整体凝聚力的核心驱动力。方向匹配方法的研究结果表明，技术与经济成本较低的相对稀疏的运动数据，可用于对比检验驱动运动决策的各类影响因子假说。