Variation in artificial light at night (ALAN) affects ecosystem functions: An experimental approach using plasticine caterpillar predation in an urban environment

Artificial Light at Night (ALAN) is changing our nocturnal landscape. Recent research reveals the negative impacts on biodiversity, including individual behaviour, phenology, physiology in a range of taxa, and shifts in community composition. However, few studies investigated how variability in ALAN impacts ecosystem functions such as predation in the illuminated landscape. We used a set of LED light poles placed along meadows in Freising, Germany, and placed sets of plasticine dummy caterpillars at different distances from the ALAN source, overnight, to measure predation between May and November 2024. We hypothesized that attack rates would be positively correlated with distance from the ALAN source, and that vegetation characteristics and moon phase would modify the impact of ALAN on predation rates. We found strong positive correlations between distance and total attack rates, arthropod attack rates, and a similar tendency in small mammals. Arthropod attacks were also significantly impacted by moon phase. We did not find any effect of distance to the ALAN source on slug attacks; their activity was evenly distributed in the landscape, but was significantly impacted by vegetation height. All groups were negatively impacted by a mowing event at the end of the season. Our results show that variability in ALAN in the lit environment can modify individual ecosystem functions, i.e., predation, in urban green landscapes, with variation at small spatial scales. It is pertinent that future studies test ALAN impacts on predation and other ecosystem functions, to understand the spatial and temporal scale of ALAN variability impacts on ecosystem functionality.