COS 277-1 - Impacts of artificial light at night (ALAN) on grassland communities propagate through different ecological pathways

Background/Question/Methods

Artificial light at night (ALAN) is a global phenomenon that affects virtually every region on Earth. Human population density will continue to increase, and so will ALAN. With an annual increase of 2-10%, ALAN is one of the most pressing drivers of current global change. As around 30% of all vertebrates and over 60% of invertebrates are nocturnal, artificial light has the potential to fundamentally disrupt species interactions, ecosystem processes, and thus entire ecosystems and their functioning. While the scientific focus to date has mostly been on how ALAN affects the physiology and behavior of species, we know very little about its consequences at the community-level. Therefore, we are still struggling to make inferences on how whole ecosystems will respond to changes in light regimes. To shed light on this, we experimentally tested community-level responses to a gradient of ALAN, including simulated moon light, using grassland communities assembled in the iDiv Ecotron facility. We measured a large set of ecological response variables ranging from invertebrate movement and predation rates across plant performance and biomass to belowground microbial communities and processes.

Results/Conclusions

We found that even the lowest ALAN intensities have an impact on animal movement, predation, and plant biomass and performance. Additionally, our structural equation modelling approach has revealed indirect pathways for effects of ALAN on plants that even propagate belowground. The far-reaching impacts on many different ecosystem processes highlight the importance of ALAN as a global change driver. Moreover, the evidence that even low light intensities have severe effects on some processes, stresses the importance of considering the wide-ranging low-intensity skyglow caused by the scattering and reflection of light in the atmosphere. Furthermore, our results provide some of the first experimental evidence demonstrating that the threat from ALAN extends beyond organisms directly exposed to light.