Light pollution in complex ecological systems

Abstract

Light pollution has emerged as a burgeoning area of scientific interest, receiving increasing attention in recent years. The resulting body of literature has revealed a diverse array of species-specific and context-dependent responses to artificial light at night (ALAN). Because predicting and generalizing community-level effects is difficult, our current comprehension of the ecological impacts of light pollution on complex ecological systems remains notably limited. It is critical to better understand ALAN's effects at higher levels of ecological organization in order to comprehend and mitigate the repercussions of ALAN on ecosystem functioning and stability amidst ongoing global change. This theme issue seeks to explore the effects of light pollution on complex ecological systems, by bridging various realms and scaling up from individual processes and functions to communities and networks. Through this integrated approach, this collection aims to shed light on the intricate interplay between light pollution, ecological dynamics and humans in a world increasingly impacted by anthropogenic lighting. This article is part of the theme issue 'Light pollution in complex ecological systems'.

Keywords: artificial light at night; community; ecosystem; global change; modelling; network.

Figure 1.

The properties of light. Artificial light possesses several physical characteristics that are crucial to understanding its impact on ecosystems, as well as to formulating informed mitigation strategies. These characteristics include: (i) spectral composition (which can have varying effects on species and ecosystems), (ii) duration and timing (e.g. the lengths of illumination periods during the night, or the precise timing of illumination), (iii) intensity (i.e. amount of light), and (iv) scattering. Light tends to become more scattered through processes such as reflection by aerosols, which typically decreases its intensity. This phenomenon is most prominent in the so-called ‘skyglow’. Images for ‘spectrum’, ‘intensity’ and ‘duration and timing’ ©pixabay. Image for ‘scattering’ ©Alessandro Della Bella. (Online version in colour.)

Figure 2.

Effects of ALAN on complex ecological systems. ALAN propagates through different levels of ecological organization. Influencing individual physiology and behaviour, it alters key ecological processes and functions, such as movement or growth, resulting in significant changes to species interactions and the complex networks they form within and across communities. Consequently, the effects of ALAN cascade to entire ecosystems, leading to profound implications for ecosystem functioning. Humans as the cause of light pollution are inherently woven into the intricate web of these impacts. While they gain direct benefits from nocturnal illumination, they also experience negative consequences either directly through, e.g. health issues, or indirectly through a chain of ecosystem feedback effects that could potentially lead to a reduction in ecosystem services. (Online version in colour.)

Figure 3.

Modelling and predicting consequences of light pollution. (a) Studies that employ only two (e.g. presence/absence) or too few light levels (i) are at risk of misinterpreting the true impact of light and (ii) limit our ability to make predictions. In the example depicted here, light intensity is thought to have a saturating effect on a certain ecosystem process or function. However, experiment A (in yellow) would fail to capture any significant effect of ALAN, while experiment B (in pink) would overlook the saturating trend. Therefore, it is essential to select an adequate number of light levels to accurately capture the complex relationships between light and organisms (b). The insights gained from fully quantitative (e.g. dose–response) relationships provide the basis to formulating theories and developing models. These models can then be employed to better predict the consequences of ALAN across various dimensions: space, time and different levels of ecological organization (c). Image for ‘space’ from Falchi et al. 2016 [33]. Image for ‘ecological organization’ ©Phillip Janta. Images for ‘time’ ©pixabay. (Online version in colour.)