COS 69-4 - Tropical ecosystem consequences of artificial light at night through moth community changes

Abstract: Artificial light at night (ALAN) is now understood as a widespread pollutant with measurable ecological consequences. ALAN is skyrocketing globally and will likely continue to pace alongside projected urbanization rates. ALAN takes two forms: large pockets of diffuse, luminous haze (sky glow) and localized, direct light. Each have distinct, but variable, biological impacts. We know that ALAN causes a suite of maladaptive physiological and behavioral responses in organisms- confusing circadian rhythms, misdirecting navigation and migration, and reducing mating success. ALAN has been linked to global insect declines recorded in the past decade, and nocturnal insects, many of which are photaxic, are particularly at risk. Understanding the extent of ALAN’s connection to insect population decline is crucial, however ALAN is confounded with land use change in most studies, making its precise impact unknown. Our study used moths to test whether ALAN has distinct and differentiable impacts from land use change. We hypothesized that study locations with high ALAN will select against photaxic moth species leading to lower overall diversity, and that regardless of light levels, highly urbanized sites will be dominated by generalist species.

We selected nine study locations representing a gradient of atmospheric light pollution and urbanization across Hong Kong. Each location had three lit sites (direct light from a streetlamp) and three dark sites (no direct light). To sample moths, we used both light traps and fruit-baited traps. Light traps offer the greatest opportunity for sampling the full moth community but suffer from urban light levels impacting trap proficiency. Fruit-baited traps avoid the confounding effects of light pollution but attract a smaller representation of the moth community. By using both trap types, we were able to control for each traps’ disadvantages. We captured over 3000 moths which we pinned and assigned to morphospecies. We are on track to complete species identification by the end of April, to then incorporate life history information into our analysis. Additionally, our collaborators in the Department of Earth Sciences at The University of Hong Kong are developing fine-scale urbanization and atmospheric light pollution maps of each of our site locations.

So far, we have discovered a significant decrease in moth abundance in the presence of ALAN. Lit sites held marginally lower moth diversity, containing a smaller subset of the community represented in dark sites. These results will likely be strengthened as we incorporate light pollution and urbanization maps into our models.