Insect communities under skyglow: diffuse night-time illuminance induces spatio-temporal shifts in movement and predation

Abstract

Artificial light at night (ALAN) is predicted to have far-reaching consequences for natural ecosystems given its influence on organismal physiology and behaviour, species interactions and community composition. Movement and predation are fundamental ecological processes that are of critical importance to ecosystem functioning. The natural movements and foraging behaviours of nocturnal invertebrates may be particularly sensitive to the presence of ALAN. However, we still lack evidence of how these processes respond to ALAN within a community context. We assembled insect communities to quantify their movement activity and predation rates during simulated Moon cycles across a gradient of diffuse night-time illuminance including the full range of observed skyglow intensities. Using radio frequency identification, we tracked the movements of insects within a fragmented grassland Ecotron experiment. We additionally quantified predation rates using prey dummies. Our results reveal that even low-intensity skyglow causes a temporal shift in movement activity from day to night, and a spatial shift towards open habitats at night. Changes in movement activity are associated with indirect shifts in predation rates. Spatio-temporal shifts in movement and predation have important implications for ecological networks and ecosystem functioning, highlighting the disruptive potential of ALAN for global biodiversity and the provision of ecosystem services. This article is part of the theme issue 'Light pollution in complex ecological systems'.

Keywords: ALAN; activity pattern; crepuscular; foraging; fragmented landscapes; light pollution.

Figure 1.

Concept illustrating how ALAN may cascade from physiological and behavioural processes (a), to interactions and functions (b), and ultimately to community and ecosystem responses (c). Orange ovals and black arrows indicate our research questions: how does ALAN affect temporal (Q1) and spatial movement activity (Q2) in a patchy habitat? Does ALAN predominantly affect predation rates through detection probabilities (Q3), or are predation rates rather driven by the effects of spatio-temporal movement activity on encounter rates between predator and prey (Q4)? (Online version in colour.)

Figure 2.

Experimental design. (a) Interior view of the grassland habitat patches established in an EcoUnit. (b) Schematic of the patch design highlighting the distribution of radio frequency identification (RFID) sensors and prey dummies across the EcoUnit. (c) EcoUnits covered with black theatre curtains to prevent cross-contamination with light. (d) Pictures of a beetle with medium-sized RFID-tag (taken from an experiment using the same tracking approach and setting, [43]) and an artificial caterpillar prey dummy with bite marks. (Online version in colour.)

Figure 3.

Movement activity (sum of detections per day/night) in response to night-time illuminance. EcoUnit-level daily movement activity (per 24 h) (a) and daytime (light blue) and night-time movement activity (dark blue) (b). Dashed lines represent non-significant relationships (p > 0.05). Shaded regions represent 95% confidence intervals. (Online version in colour.)

Figure 4.

Movement activity (sum of detections per day/night) in habitat patches (green) and matrix (orange) in response to night-time illuminance during the day (a) and night (b). Dashed lines represent non-significant relationships (p > 0.05). Shaded regions represent 95% confidence intervals. (Online version in colour.)

Figure 5.

(a) EcoUnit-level predation rate (bite counts per 14 days) in response to night-time illuminance. (b) Patch-level predation rate (bite counts per 14 days per patch) in response to patch-level movement activity (sum of detections per 14 days per patch, figure 2). Dashed lines represent non-significant relationships (p > 0.05). Shaded regions represent 95% confidence intervals. (Online version in colour.)