Population to Ecosystem Level Impacts of Artificial Light at Night

Humans drive global change in a myriad of ways (Nelson et al. 2006), one of which is the introduction of artificial light at night (ALAN, Gaston et al. 2014). The intrusion of ALAN into nighttime environments is likely to have profound ecological consequences as a result of disruption to natural variations in light availability (Gaston et al. 2013; Gaston et al. 2014). Recent efforts have begun to uncover the ramifications of ALAN for populations, communities, and ecosystems. However, research on the ecological effects of ALAN is still relatively novel. Researchers studying ALAN face the additional challenge of chasing a moving target, as new lighting technologies emerge with time. In this dissertation, I explore the ways in which ALAN from increasingly popular broad-spectrum light emitting diodes affect populations, communities, and ecosystem processes. Despite their reliance on light as both an energy and information source (Gaston et al. 2013), relatively little work has addressed the effects of ALAN on plants in nature. In my second chapter, I tested the interactive effects of ALAN, intraspecific competition, and soil moisture on the growth and anti-herbivore defense of an herbaceous perennial. I found that ALAN affected plant growth, as well as had interactive effects with both competition and soil moisture on plant growth. These results highlight the complex ways ALAN may affect wild plants. ALAN is known to affect ground-dwelling arthropod community composition and trophic structure (Davies et al. 2012; Davies et al. 2017; McMunn et al. 2019; Heiling 1999). Terrestrial arthropod communities contribute to decomposition, an ecosystem process by which nutrients are returned to the soil, and which is affected by trophic structure of litter layer invertebrates (Wall & Moore 1999; Moore et al. 2004). Therefore, in my third chapter I tested the effects of ALAN on the litter-layer invertebrate community and whether these impacted the breakdown of plant litter. My results confirmed the findings of others that ALAN increases local abundances of secondary and tertiary consumer arthropods (Davies et al. 2012; Davies et al. 2017; McMunn et al. 2019; Yuen & Bonebrake 2017; Miller et al. 2017), however this did not depress the rate of decomposition under ALAN conditions. Another way in which terrestrial arthropods can influence nutrient dynamics is via dispersal (Yang & Gratton 2014; Hu et al. 2017; McInturf et al. 2019), because nitrogen in arthropods, and in particular insects, is quickly returned to the soil (Yang & Gratton 2014; Behie & Bidochka 2013). Attraction of arthropods to sources of ALAN may alter their dispersal (Eisenbeis 2006) and subsequently nutrient distribution. In my fourth chapter I tested the effects of ALAN on net fluxes (measured as attraction – repulsion) and local abundances of terrestrial arthropods. I found that some flying insects demonstrated net attraction to ALAN sources and effects of ALAN on local abundances varied substantially among arthropod taxonomic groups. Taken in totality, the work presented in my dissertation furthers our understanding of how ALAN affects plants and arthropods at population and community levels, new insights on impacts of ALAN-induced shifts in trophic structure and spatial redistribution of nutrients on ecosystem processes.