When most people hear the term “global change” they might think of habitat loss or climate change or species invasions. But one type of change that has gotten less attention is the increasing occurrence of artificial light at night or ALAN. Wherever humans build cities and have electric power, light at night is present on the landscape, and ALAN continues to increase by almost 10% each year. But it wasn’t always this way. Up until almost 150 years ago, the earth was a very dark place at night, with only moonlight, starlight, and some human-created fires to illuminate the environment. While research has shown that ALAN can have strong negative impacts on human health, we know comparatively little about how ALAN impacts wildlife.
Research into the impacts of ALAN on anoles forms the core of my National Science Foundation-sponsored postdoctoral fellowship. Anoles are a great system in which to study ALAN because they are exposed to ALAN frequently when they exploit urban habitats (which is often!), and we have a solid knowledge of many of the traits, such as behavior, physiology, and reproduction, which mediate potential impacts of ALAN.
Last spring, I conducted a lab experiment with undergraduate Amanda Merritt and my postdoctoral advisor, Jason Kolbe, to examine the impacts of ALAN on reproduction in brown anoles. Contrary to our expectations that ALAN would stress the lizards and reduce reproduction, we instead found that ALAN actually caused increased growth and reproductive output in some lizards, did not increase levels of corticosterone (a stress hormone), and did not have negative effects on hatchling survival or size. This research indicates that, in at least some contexts, light at night can be beneficial for organisms!
To follow up on this labwork, this spring I initiated a large scale field-based project to investigate how ALAN affects many aspects of anoles’ life histories. I began by marking and monitoring anoles at a botanical garden without nocturnal light sources for over a month to gather baseline data. I then introduced artificial light at night into certain parts of the garden and tracked lizards’ locations, gathered blood samples to measure stress and energy levels, and recaptured and measured them to track their growth and survival. Analyses are ongoing, but our preliminary results indicate that lizards did not avoid areas with artificial lights and that this may reduce their blood glucose levels, potentially impacting their energy reserves. More results to follow!
Featured image credit: NASA