Ecological impacts of artificial light at night on arthropod communities
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Date
2025
Publication Type
Doctoral Thesis
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Abstract
The world is facing numerous challenges directly or indirectly linked to biodiversity loss. One of these challenges is artificial light at night (ALAN). While ALAN is considered indispensable in our modern society and is often associated with the feeling of safety, it illuminates more than half of the Earth’s surface and continues to expand at an alarming rate of 2-6% per year. It is increasingly recognized as one of the major drivers of ecological change in the 21st century, with documented negative impacts not only on humans but whole natural ecosystems.
ALAN has been identified as one of the key contributors to the global decline of arthropods, particularly insects. Arthropods are essential to ecosystem functioning because they provide essential services including pollination, decomposition, nutrient cycling, and pest control. However, ALAN can disrupt their circadian rhythm and interfere with behaviors critical for survival. It can disorient individuals, interfere with navigation and mating systems, alter foraging behavior, and increase their vulnerability to exhaustion and predation. These disruptions can reduce arthropod abundance and diversity, alter species interactions, and impair vital ecosystem services.
The ecological impacts of ALAN are shaped by multiple interacting dimensions: spectral composition, light intensity, temporal and spatial configuration. These dimensions interact with each other and can create complex patterns of nighttime light exposure. Organisms react in distinct ways to specific light exposure and lighting characteristics. The ecological impact of ALAN cannot be fully understood without considering the full range of technical parameters involved in modern outdoor lighting. The rapid development of light emitting diode (LED) lighting systems—offering low maintenance, long-lasting, and energy efficient solutions—has accelerated the expansion of global light pollution but also offers new opportunities for mitigation. Unlike earlier lighting technologies, LED systems allow the precise adjustment of key lighting properties, such as spectral distribution (color temperature), light intensity (dimmability), and luminaire shape design. These adjustments can help finding more ecologically sensitive outdoor lighting solutions.
In this thesis I investigate how different LED-light characteristics affect ground-dwelling and flight-active arthropod communities (field experiments) and individual species (laboratory experiment). I tested three color temperatures (3700 K, 2900 K and 2200 K), two light levels (dimmed to 50% intensity and 100% full intensity), and two luminaire shapes (focused vs. diffused). The goal was to develop mitigation strategies for more sustainable outdoor lighting using commercially available luminaires.
In Chapter 1 I provide an introduction to the importance of arthropods for global ecosystems and summarize the current knowledge on the negative impacts of ALAN, as well as the existing knowledge gaps. In Chapter 2, I wanted to address the knowledge gap on how ALAN affects ground-dwelling arthropods, a largely overlooked group. I therefore investigated the impacts of the combined LED characteristics (light color temperatures, light levels and luminaire shapes)—both individually and in combination—on functional ground-dwelling arthropod groups. This approach helps to reveal how ALAN can alter community composition and trophic dynamics on the ground-level. In Chapter 3, because most ALAN studies focus only on one arthropod group—mainly flight-active arthropods—I expended the scope to examine the impacts of different LED characteristics (the same as in Chapter 2) on both flight-active and ground-dwelling arthropods. This allowed me to evaluate whole-community responses and compare the impacts between the two groups. It offered a more complete picture of the ecosystem-wide impact of ALAN and helped better identify lighting strategies that can reduce the negative impacts on arthropods. Chapter 4 focuses on how ALAN—using two LED color temperatures—affects the development across life stages in a nocturnal moth species, the spongy moth. As most ALAN research targets the impacts on abundances of adult individuals, this species level approach focusing on earlier life stages provides insights into how ALAN can influence growth and fitness, processes critical for population dynamics. In Chapter 5 I summarize my contributions to the field of ALAN resulting from this thesis, put them into a broader context and consider limitations and possible future directions of my work.
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Examiner : Bolliger , Janine
Examiner : Gossner, Martin
Examiner : Pellissier , Loic
Examiner : Schuldt , Andreas
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ETH Zurich
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Subject
artificial light at night; light pollution; Insects; Arthropods
Organisational unit
02350 - Dep. Umweltsystemwissenschaften / Dep. of Environmental Systems Science