Predicting movement speed of beetles from body size and temperature

Abstract

Movement facilitates and alters species interactions, the resulting food web structures, species distribution patterns, community structures and survival of populations and communities. In the light of global change, it is crucial to gain a general understanding of how movement depends on traits and environmental conditions. Although insects and notably Coleoptera represent the largest and a functionally important taxonomic group, we still know little about their general movement capacities and how they respond to warming. Here, we measured the exploratory speed of 125 individuals of eight carabid beetle species across different temperatures and body masses using automated image-based tracking. The resulting data revealed a power-law scaling relationship of average movement speed with body mass. By additionally fitting a thermal performance curve to the data, we accounted for the unimodal temperature response of movement speed. Thereby, we yielded a general allometric and thermodynamic equation to predict exploratory speed from temperature and body mass. This equation predicting temperature-dependent movement speed can be incorporated into modeling approaches to predict trophic interactions or spatial movement patterns. Overall, these findings will help improve our understanding of how temperature effects on movement cascade from small to large spatial scales as well as from individual to population fitness and survival across communities.

Keywords: Allometry; Climate warming; Ectotherms; Exploratory speed; Image-based tracking; Movement ecology; Thermal response.

Fig. 1

The experimental setup of the automated image-based tracking of beetles in an environmental reach-in chamber. A Sketch of the experimental setup. B Sketch of an automated image-based tracking sequence including x- and y-coordinates for each timestamp. C Actual experimental setup in an environmental reach-in chamber

Fig. 2

The unimodal scaling of exploratory speed [ms⁻¹] with temperature [°C] of carabid beetles (n = 125, number of species = 8). A Five different thermal performance models included in the rTPC package [59] in comparison. B The final selected model based on AIC comparison (Table 2), a modified Sharpe-Schoolfield equation (pawar model, [50], blue curve). Gray curves show the other tested models in comparison

Fig. 3

A The predicted scaling of movement speed [ms⁻¹] with temperature [°C] for three different body masses [mg] (blue color scale) based on Eq. (1). B The predicted scaling of movement speed [ms⁻¹] with body mass [mg] for three different temperature levels [°C] (orange-dark red color code)