Artificial Light at Night (ALAN) impacts over 20% of the earth’s surface and is rapidly increasing at an estimated 6% per year, disrupting ecological interactions and individual physiology. Compared to sea turtles or invertebrates, few studies have focused on the effects of ALAN on amphibians. Amphibians across the globe are facing drastic declines, many of which thought to be partly caused by anthropogenic disturbances like ALAN. We tested whether ALAN affected American toads (Bufo americanus) through either directly impacting individual toads or by altering the toads’ ecological community. To determine the effect of ALAN over multiple amphibian life-stages, we conducted a two-phase experiment using outdoor mesocosms and indoor terraria. In the first phase, we raised toad larvae using a 2x2x2 factorial design manipulating the presence and absence of ALAN, opportunity for colonization (presence or absence of lids to control insect colonization) and the presence or absence of toads. We measured treatment effects on toad traits (growth, development, survival) and ecological community traits (algal growth, invertebrate abundance). In the second phase, we moved metamorphosing toads into laboratory terraria where they were separated into two post-metamorphic photoperiod treatments: ALAN or natural. We measured juvenile toad growth, survival and activity over 12 weeks.
Results/Conclusions
In the first phase, larval toad survival and mass at metamorphosis was not affected by ALAN or the interaction between ALAN and colonization. Days to metamorphosis was significantly reduced by one day in the presence of ALAN and eight days in the absence of colonization but was not affected by their interaction. Periphyton biomass was not affected by colonization or toad presence but was significantly reduced by ALAN. These results suggest ALAN has important direct effects on amphibians and a lesser effect on the ecological community. In the second phase, we tested if post-metamorphic toads were affected by larval stage carry-over effects or current post-metamorphic exposure of ALAN. Post-metamorphic toad survival was not affected by ALAN exposure in the larval or post-metamorphic stage or their interaction. Larval ALAN did however, further reduce activity suggesting ALAN carry-over effects were present. Post-metamorphic toad growth was significantly reduced by 15% when exposed to ALAN as juveniles. Toad activity in the laboratory was significantly increased when exposed to ALAN indicating ALAN toads remain active both day and night. Expanding our experiment to post-metamorphic life-stages not only revealed a carry-over effect but also suggested that short-term exposure to ALAN can increase activity and reduce growth.