Light pollution is the fastest growing potential threat to firefly conservation in the Atlantic Forest hotspot

Abstract In addition to being threatened by habitat loss derived from deforestation and urbanisation, fireflies are further deeply impacted by light pollution, which impairs their unique use of light signals to communicate and track females. The impact of stressors that can lead to declines in firefly populations is poorly known in the southern hemisphere, including the Atlantic Forest where they are especially diverse, associated with lack of knowledge about their distributions. Here, we model the potential distribution of the tracker ghost firefly Amydetes fastigiata and investigate whether light pollution, urbanisation and deforestation are increasing over time in this area. We found that light pollution is the stressor with the most prominent increase rates over its distribution. Light pollution is significantly increasing in extent and intensity over time, outpassing urbanisation and deforestation which increased at lower rates. Protected areas successfully buffer effects of urbanisation and deforestation, but are incapable to halt the spread of light pollution. Increasing light pollution is especially concerning due to the spotlighting behaviour of A. fastigiata to track females through the night, which is imperilled by overshadowing lights. Light pollution trends are increasing fast and should be considered as a significant stressor even within protected areas – which calls for a reform in regional conservation policies and designation of new areas to be prioritised. We presented a framework for the evaluation of threat rates based on species distribution models that can foster future research and assess vulnerabilities of important species facing global change.