Night-Lights: Light Pollution Impacts on Fireflies and Arthropod Communities

Light pollution⎯artificial nighttime illuminance from luminaries such as streetlights⎯ has dramatically brightened the nighttime landscape (Gaston et al. 2014), envelops an increasingly large portion of the globe, and is continuing to spread (Falchi et al. 2016a, Kyba et al. 2017). Given the biological importance of light as a resource, information source (Gaston et al. 2013), and circadian organizer of activities (Kantermann 2013, Fonken and Nelson 2014), the consequences of light pollution for living organisms are expected to be wide-ranging and complex (Gaston et al. 2014). In this dissertation, I examined light pollution impacts on arthropods, with a particular spotlight on fireflies. Fireflies are interesting model organisms for this work because many firefly species produce bioluminescent flashes that they use to communicate with potential mates during courtship prior to mating. In chapters 1 and 2, I explore light pollution effects on firefly flash courtship behaviors, movement, and local abundances. My results show that light pollution decreased firefly flash conversations and mating, attracted fireflies, and reduced local abundances of one species. Taken together, these findings suggest light pollution may create demographic traps, luring fireflies into places where they may be less likely to mate. In Chapter 3, I investigate whether firefly abundances and species richness are associated light pollution and urban land cover across large areas. I accomplished this by surveying fireflies across Virginia, and by comparing my survey data with data emerging from Firefly Watch, a national citizen science firefly monitoring program. In addition to finding similar trends in data collected by a professional scientist and by citizen scientists, I showed local light pollution (i.e., within residential properties) to be negatively associated with firefly abundance and species richness. Finally, in Chapter 4, I examined light pollution impacts on arthropod abundances and trophic structure in a two-year manipulative field experiment. My results show a slight increase in arthropod abundances in illuminated versus unilluminated plots in the first year of sampling, but no impact on abundances in the second year of sampling, and no impact on trophic structure. Overall, my work suggests light pollution effects on arthropods may be complex, affecting multiple aspects of a species’ behavior, demography, and ecology, and points to the advantages of taking a multi-faceted approach linking small-scale manipulative field studies with larger-scale surveys to illuminate impacts of light pollution on arthropods.