Bright lights, big city: an experimental assessment of short-term behavioral and performance effects of artificial light at night on Anolis lizards

Abstract

With urbanization expanding into natural areas, it is increasingly important to understand how species subject to human-induced habitat alteration respond to novel opportunities and stressors. A pervasive consequence of urbanization is artificial light at night (ALAN), which previous studies have found introduces both costs and benefits for vertebrates. This understanding, however, primarily reflects findings from laboratory-controlled experiments or comparisons of wild populations in areas with long-standing differences in ALAN regimes. Here, we investigated the short-term costs and benefits for Anolis lizards during the period of initial exposure to ALAN using realistic light levels for urban areas (mean ± SD = 87.9 ± 36.7 lx at a distance of 3 m). As compared to controls, we hypothesized that adding ALAN would result in behavioral and physiological changes over the short term for brown anoles and their arthropod prey. In contrast to predictions, ALAN did not increase arthropod abundance or extend anole activity into the night. Structural habitat and sleep site use changed little in response to ALAN, which exposed about one-third of sleeping anoles in ALAN plots to light at night due to our manipulation. However, this direct light exposure resulted in lizards being more easily roused from sleep compared to lizards sleeping in the dark in control plots or in shadows in ALAN plots. The apparent inability of some anoles to adjust their sleep sites to avoid ALAN exposure may have contributed to their increased responsiveness at night and decreased locomotor endurance in the day. Our study suggests brown anoles can experience higher short-term costs than benefits during initial exposure to ALAN.