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Recording fine-scale movement of ground beetles by two methods: Potentials and methodological pitfalls

Citation

Růžičková, Jana; Elek, Zoltán (2022), Recording fine-scale movement of ground beetles by two methods: Potentials and methodological pitfalls, Dryad, Dataset, https://doi.org/10.5061/dryad.79cnp5hvj

Abstract

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 (SEM = 0.181 m) for distances and 31.330° (SEM = 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.

Methods

Datasets contain fine-scale trajectories and movement parameters collected by two different methods - distance-bearing and GPS device - in two different experiments. In the first experiment, we artificially generated trajectories mimicking the movement of ground beetles. In the second experiment, we radio-tracked six individuals of large ground beetle Carabus coriaceus in a managed temperate forest.

For each experiment, we provide three csv files containing (1) dataset for linear mixed modeling (long/lat coordinates, distances, turning angles, and consequent measurement errors between recording methods), (2) trajectory dataset for Hidden Markov models (long/lat coordinates, track ID and time) and (3) dataset with decoded movement states by Viterbi algorithm and total length of a particular trajectory. Finally, an R script is also included where we describe in detail all used datasets and functions to get results provided in the final publication