Růžičková Jana, Elek Zoltán
MTA-ELTE-MTM Ecology Research Group Biological Institute, Eötvös Loránd University Budapest Hungary.
Ecol Evol. 2021 May 16;11(13):8562-8572. doi: 10.1002/ece3.7670. eCollection 2021 Jul.
Movement trajectories are usually recorded as a sequence of discrete movement events described by two parameters: step length (distance) and turning angle (bearing). One of the most widespread methods to record the geocoordinates of each step is by a GPS device. Such devices have limited suitability for recording fine movements of species with low dispersal ability including flightless carabid beetles at small spatio-temporal scales. As an alternative, the distance-bearing approach can avoid the measurement error of GPS units since it uses directly measured distances and compass azimuths. As no quantification of measurement error between distance-bearing and GPS approaches exists so far, we generated artificial fine-scale trajectories and in addition radio-tracked living carabids in a temperate forest and recorded each movement step by both methods. Trajectories obtained from distance-bearing were compared to those obtained by a GPS device in terms of movement parameters. Consequently, both types of trajectories were segmented by state-switching modeling into two distinct movement stages typical for carabids: random walk and directed movement. We found that the measurement error of GPS compared to distance-bearing was 1.878 m ( = 0.181 m) for distances and 31.330° ( = 2.066°) for bearings. Moreover, these errors increased under dense forest canopy and rainy weather. Distance error did not change with increasing distance recorded by distance-bearing but bearings were significantly more sensitive to error at short distances. State-switching models showed only slight, not significant, differences in movement states between the two methods in favor of the random walk in the distance-bearing approach. However, the shape of the GPS-measured trajectories considerably differed from those recorded by distance-bearing caused especially by bearing error at short distances. Our study showed that distance-bearing could be more appropriate for recording movement steps not only of ground-dwelling beetles but also other small animals at fine spatio-temporal scales.
运动轨迹通常被记录为一系列离散的运动事件，由两个参数描述：步长（距离）和转向角（方位）。记录每个步的地理坐标最广泛使用的方法之一是通过全球定位系统（GPS）设备。此类设备在记录扩散能力低的物种的精细运动方面适用性有限，包括在小时空尺度下的不会飞的步甲科甲虫。作为一种替代方法，距离 - 方位法可以避免GPS设备的测量误差，因为它使用直接测量的距离和罗盘方位。由于目前不存在距离 - 方位法与GPS法之间测量误差的量化，我们生成了人工精细尺度轨迹，此外还在温带森林中对活体步甲进行无线电跟踪，并通过两种方法记录每个运动步。从距离 - 方位法获得的轨迹在运动参数方面与通过GPS设备获得的轨迹进行了比较。因此，两种类型的轨迹都通过状态切换建模被分割为步甲典型的两个不同运动阶段：随机行走和定向运动。我们发现，与距离 - 方位法相比，GPS在距离方面的测量误差为1.878米（ = 0.181米），在方位方面为31.330°（ = 2.066°）。此外，在茂密的森林树冠和雨天条件下，这些误差会增加。距离误差不会随着距离 - 方位法记录的距离增加而变化，但方位在短距离时对误差明显更敏感。状态切换模型显示，两种方法在运动状态上只有轻微的、不显著的差异，距离 - 方位法更倾向于随机行走。然而，GPS测量的轨迹形状与距离 - 方位法记录的轨迹有很大不同，特别是由于短距离时的方位误差。我们的研究表明，距离 - 方位法不仅可能更适合记录地面甲虫的运动步，而且在精细的时空尺度下也适合记录其他小型动物的运动步。
