Illuminating the effects of light pollution on fireflies
Artificial light pollution is an emerging ecological threat. Light from human activities already compromises night sky darkness for 20% percent of the terrestrial surface of the Earth. As continued development aggravates the scope and severity of light pollution, predicting the responses of biological systems is critical. This is especially important for twilight- and night-active organisms such as fireflies (Coleoptera; Lampyridae). To attract mates, many adult fireflies produce bioluminescent signals from abdominal, light-emitting organs. Light pollution has been associated with reduced firefly activity in a handful of recent studies, but ours is likely the first to examine how light pollution affects firefly abundances and mating success in a manipulated field experiment. We randomly assigned 3 light pollution treatments (no light, medium, high) to field plots and counted firefly (Photinus pyralis) flashes and individuals within each plot over the course of 5 nights. We also measured firefly mating opportunities in the field under manipulated brighter and darker conditions.
We observed significantly fewer firefly flashes in brighter plots, but captured similar numbers of fireflies across light treatment levels. Based on these findings, we suggest that light pollution reduces firefly flash activities without necessarily reducing local firefly abundances in the short term. However, the potential for long-term demographic effects of light pollution remains. There was a significant 114% in female responses to the courtship flashes of nearby males in artificially lit vs. unlit plots. Thus, we suggest that reduced female fecundity in light polluted areas is one mechanism potentially driving low firefly abundances in light polluted areas. Our work contributes to the growing body of literature on the consequences of light pollution and other anthropogenic disturbances for animal communication, fitness, and population dynamics.