Light pollution creates multiple threats to the movement ecology of nocturnal arthropod taxa

Light pollution is a major contributing factor to declines in global biodiversity that is steadily increasing in both severity and spatial extent. Artificial light at night degrades the natural visual environment by distorting and masking information vital to various nocturnal animal behaviors. In this study, we demonstrate that multiple discrete behavioral impacts of light pollution can occur simultaneously in different ecological contexts, potentially amplifying the negative consequences of light at night. We detail how artificial light at the ecologically critical transition between day and night modifies the nocturnal activity patterns of two ecologically distinct and phylogenetically distant terrestrial nocturnal arthropods: the long-distance migratory moth Helicoverpa armigera and the central-place foraging spider Drassodes. Moreover, we show that the same timing and levels of light pollution disrupt the celestial nocturnal pattern of polarized light, a visual cue used by these and other species for navigation. We suggest that the concurrent effects of a single anthropogenic stressor can be synergistic and stress the importance of reviewing the relationships between the multiple effects of single stressors when evaluating their impacts.