Artificial light at night alters grassland vegetation species composition and phenology

Let there be Skyglow-light pollution from a large outdoor music festival (Lollapalooza Berlin 2016)

Live music is often linked to elaborate light shows, particularly at large outdoor music festivals. However, artificial light at night is one form of environmental pollution, light pollution, and because outdoor festivals emit a substantial amount of artificial light into the environment, they are a potential source of light pollution. So far, no studies that quantified the impact of such festivals on urban light pollution and skyglow exist. Here, the light pollution produced by a major rock festival (Lollapalooza Berlin 2016 with 70,000 visitors per day in an urban park) was investigated with ground-based radiometry and night-time light data. A small night-sky radiometer installed near the main stages and a calibrated digital camera from a nearby observation spot inside of the park were used to quantify changes in night sky brightness and direct light emissions within the park. The impact of the music festival on the urban skyglow was indeed measurable. Zenith luminance increased locally by up to a factor of 8 and illuminance increased by about 50% at the observation spot within the park. The radiance detected by night-time satellite was also increased during the festival. This is the first time, that light pollution from such a major rock music event was quantified.

Artificial light at night reduces earthworm activity but increases growth of invasive ragweed

BACKGROUND

Artificial light at night, also referred to as light pollution (LP), has been shown to affect many organisms. However, little is known about the extent to which ecological interactions between earthworms and plants are altered by LP. We investigated the effects of LP on anecic earthworms (Lumbricus terrestris) that come to the surface at night to forage and mate, and on the germination and growth of the invasive and allergenic ragweed (Ambrosia artemisiifolia). In a full factorial pot experiment in the greenhouse, we tested four factors and their interactions: LP (5 lux vs. 0 lux at night), earthworms (two individuals vs. none), plant species (seeding of ragweed only vs. mixed with Phacelia seeds) and sowing depth (seed placed at the surface vs. in 5 cm depth). Data were analysed using Generalized Linear (Mixed) Models and multifactorial ANOVAs with soil parameters as covariates.

RESULTS

Light pollution reduced earthworm surface activity by 76% as measured by casting activity and toothpick index; 85% of mating earthworms were observed in the absence of LP. Light pollution in interaction with earthworms reduced ragweed germination by 33%. However, LP increased ragweed height growth by 104%. Earthworms reduced ragweed germination especially when seeds were placed on the soil surface, suggesting seed consumption by earthworms.

CONCLUSIONS

Our data suggest that anecic earthworms are negatively affected by LP because reduced surface activity limits their ability to forage and mate. The extent to which earthworm-induced ecosystem services or community interactions are also affected by LP remains to be investigated. If the increased height growth of ragweed leads to increased pollen and seed production, it is likely that the competition of ragweed with field crops and the risks to human health will also increase under LP.

Artificial light at night decreases plant diversity and performance in experimental grassland communities

Artificial light at night (ALAN) affects many areas of the world and is increasing globally. To date, there has been limited and inconsistent evidence regarding the consequences of ALAN for plant communities, as well as for the fitness of their constituent species. ALAN could be beneficial for plants as they need light as energy source, but they also need darkness for regeneration and growth. We created model communities composed of 16 plant species sown, exposed to a gradient of ALAN ranging from 'moonlight only' to conditions like situations typically found directly underneath a streetlamp. We measured plant community composition and its production (biomass), as well as functional traits of three plant species from different functional groups (grasses, herbs, legumes) in two separate harvests. We found that biomass was reduced by 33% in the highest ALAN treatment compared to the control, Shannon diversity decreased by 43% and evenness by 34% in the first harvest. Some species failed to establish in the second harvest. Specific leaf area, leaf dry matter content and leaf hairiness responded to ALAN. These responses suggest that plant communities will be sensitive to increasing ALAN, and they flag a need for plant conservation activities that consider impending ALAN scenarios. This article is part of the theme issue 'Light pollution in complex ecological systems'.

Long-term exposure to experimental light affects the ground-dwelling invertebrate community, independent of light spectra

Our planet endures a progressive increase in artificial light at night (ALAN), which affects virtually all species, and thereby biodiversity. Mitigation strategies include reducing its intensity and duration, and the adjustment of light spectrum using modern light emitting diode (LED) light sources. Here, we studied ground-dwelling invertebrate (predominantly insects, arachnids, molluscs, millipedes, woodlice and worms) diversity and community composition after 3 or 4 years of continued nightly exposure (every night from sunset to sunrise) to experimental ALAN with three different spectra (white-, and green- and red-dominated light), as well as for a dark control, in natural forest-edge habitat. Diversity of pitfall-trapped ground-dwelling invertebrates, and the local contribution to beta diversity, did not differ between the dark control and illuminated sites, or between the different spectra. The invertebrate community composition, however, was significantly affected by the presence of light. Keeping lights off during single nights did show an immediate effect on the composition of trapped invertebrates compared to illuminated nights. These effects of light on species composition may impact ecosystems by cascading effects across the food web. This article is part of the theme issue 'Light pollution in complex ecological systems'.

How artificial light at night may rewire ecological networks: concepts and models

Artificial light at night (ALAN) is eroding natural light cycles and thereby changing species distributions and activity patterns. Yet little is known about how ecological interaction networks respond to this global change driver. Here, we assess the scientific basis of the current understanding of community-wide ALAN impacts. Based on current knowledge, we conceptualize and review four major pathways by which ALAN may affect ecological interaction networks by (i) impacting primary production, (ii) acting as an environmental filter affecting species survival, (iii) driving the movement and distribution of species, and (iv) changing functional roles and niches by affecting activity patterns. Using an allometric-trophic network model, we then test how a shift in temporal activity patterns for diurnal, nocturnal and crepuscular species impacts food web stability. The results indicate that diel niche shifts can severely impact community persistence by altering the temporal overlap between species, which leads to changes in interaction strengths and rewiring of networks. ALAN can thereby lead to biodiversity loss through the homogenization of temporal niches. This integrative framework aims to advance a predictive understanding of community-level and ecological-network consequences of ALAN and their cascading effects on ecosystem functioning. This article is part of the theme issue 'Light pollution in complex ecological systems'.

Dim artificial light at night alters gene expression rhythms and growth in a key seagrass species (Posidonia oceanica)

Artificial light at night (ALAN) is a globally spreading anthropogenic stressor, affecting more than 20% of coastal habitats. The alteration of the natural light/darkness cycle is expected to impact the physiology of organisms by acting on the complex circuits termed as circadian rhythms. Our understanding of the impact of ALAN on marine organisms is lagging behind that of terrestrial ones, and effects on marine primary producers are almost unexplored. Here, we investigated the molecular and physiological response of the Mediterranean seagrass, Posidonia oceanica (L.) Delile, as model to evaluate the effect of ALAN on seagrass populations established in shallow waters, by taking advantage of a decreasing gradient of dim nocturnal light intensity (from < 0.01 to 4 lx) along the NW Mediterranean coastline. We first monitored the fluctuations of putative circadian-clock genes over a period of 24 h along the ALAN gradient. We then investigated whether key physiological processes, known to be synchronized with day length by the circadian rhythm, were also affected by ALAN. ALAN influenced the light signalling at dusk/night in P. oceanica, including that of shorter blue wavelengths, through the ELF3-LUX1-ZTL regulatory network, and suggested that the daily perturbation of internal clock orthologs in seagrass might have caused the recruitment of PoSEND33 and PoPSBS genes to mitigate the repercussions of a nocturnal stress on photosynthesis during the day. A long-lasting impairment of gene fluctuations in sites characterised by ALAN could explain the reduced growth of the seagrass leaves when these were transferred into controlled conditions and without lighting during the night. Our results highlight the potential contribution of ALAN to the global loss of seagrass meadows, posing questions about key interactions with a variety of other human-related stressors in urban areas, in order to develop more efficient strategies to globally preserve these coastal foundation species.

Shedding light on the effects of LED streetlamps on trees in urban areas: Friends or foes?

Streetlamp illumination disturbs the natural physiological processes and circadian rhythms of living organisms, including photosynthesizing "citizens". The light-emitting diode (LED) technology has replaced high-pressure sodium lamps. Therefore, the effects of LED streetlamps on urban trees need to be elucidated as these new lamps have a different light spectrum (with a peak in the blue and red regions of the spectrum, i.e., highly efficient wavebands for photosynthesis) compared to older technologies. To address the above-mentioned issue, two widely utilised tree species in the urban environment, including Platanus × acerifolia (P) and Tilia platyphyllos (T), were grown with or without the effect of LED streetlamps using two realistic illumination intensities (300 and 700 μmol m^-2 s^-1). Gas exchanges and biochemical features (starch, soluble sugar, and chlorophyll content) of illuminated vs non-illuminated trees were compared during the whole vegetative season. Our results showed that both tree species were strongly influenced by LED streetlamps at physiological and biochemical levels. Specifically, the mature leaves of P and T streetlamp-illuminated trees had a lower CO₂ assimilation rate at dawn and had higher chlorophyll content, with lower starch content than controls. Our results showed that the differences between the effects of the two selected light intensities on the physiochemical attributes of P and T trees were not statistically significant, suggesting the absence of a dose-dependent effect. The most significant difference between T and P trees concerning the LED-triggered species-specific effect was that the delay in winter dormancy occurred only in P individuals. This study provided insights into the extent of LED streetlamp disturbance on trees. Our findings might raise awareness of the necessity to provide less impacting solutions to improve the wellness of trees in the urban environment.

Phenology of grassland plants responds to urbanization

Understanding phenological responses of plants to changing temperatures is important because of multiple associated ecological consequences. Cities with their urban heat island can be used as laboratories to study phenological adaptation to climate change. However, previous phenology studies focused on trees and did not disentangle the role of micro-climate and urban structures.

We studied reproductive phenology of dry grassland species in response to micro-climate and urbanization in Berlin, Germany. Phenological stages were recorded weekly at the individual plant level for five native grassland species across 30 dry grassland sites along an urbanization and temperature gradient. We estimated 50% onset probabilities for flowering and seed maturation of populations, and analysed variation in onset dates using regression models.

Early flowering species significantly advanced flowering phenology with increasing mean air temperature but were little influenced by urbanization. By contrast, late-flowering species showed significant phenological responses to both air temperature and urbanization, possibly because micro-climate was most affected by urbanization in late summer. Surprisingly, not all grassland species showed an advanced phenology with increasing intensity of urbanization.

This contradicts observed patterns for urban trees, indicating that phenological shifts in urban areas cannot be generalized from the observation of one growth form or taxonomic group. Growth form appears as a possible determinant of phenological responses. Results suggest that the phenology of dry grassland species may directly respond to the urban heat island, albeit with variable direction and magnitude. This has implications for ecosystem services, shifted allergy seasons, changes of biogeochemical cycles and potential ecological mismatches.

Artificial light at night promotes bottom-up changes in a woodland food chain

Artificial light at night (ALAN) is a recognised disruptor of biological function and ecological communities. Despite increasing research effort, we know little regarding the effect of ALAN on woody plants, including trees, or its indirect effects on their colonising invertebrates. These effects have the potential to disrupt woodland food webs by decreasing the productivity of invertebrates and their secretions, including honeydew and lerps, with cascading effects on other fauna. Here, we cultivated juvenile river red gums (Eucalyptus camaldulensis) for 40 weeks under experimentally manipulated light (ALAN) or naturally dark (control) conditions. To assess direct impacts on tree growth, we took multiple measures of growth at four time periods, and also measured physiological function, biomass and investment in semi-mature trees. To assess experimentally the direct and indirect (tree-mediated) impacts of ALAN on invertebrates, from 19 weeks onwards, we matched and mismatched trees with their original ALAN environments. We colonised trees with a common herbivore of E. camaldulensis, the red gum lerp psyllid (Glycaspis nr. brimblecombei) and then measured the effects of current and historic tree lighting treatment on the psyllid life cycle. Our data revealed direct effects of ALAN on tree morphology: E. camaldulensis trees exposed to ALAN shifted biomass allocation away from roots and into leaves and increased specific leaf area. However, while the intensity of ALAN was sufficient to promote photosynthesis (net carbon gain) at night, this did not translate into variation in tree water status or photosystem adaptation to dim night-time light for ALAN-exposed trees. We found some evidence that ALAN had broad-scale community effects-psyllid nymphs colonising ALAN trees produced more lerps-but we found no other direct or indirect impacts of ALAN on the psyllid life cycle. Our results suggest that trees exposed to ALAN may share morphological responses with trees under dim daylight conditions. Further, ALAN may have significant 'bottom-up' effects on Eucalyptus woodland food webs through both trees and herbivores, which may impact higher trophic levels including woodland birds, mammals and invertebrates.

Long‐term effects of artificial nighttime lighting and trophic complexity on plant biomass and foliar carbon and nitrogen in a grassland community

The introduction of artificial nighttime lighting due to human settlements and transport networks is increasingly altering the timing, intensity, and spectra of natural light regimes worldwide. Much of the research on the impacts of nighttime light pollution on organisms has focused on animal species. Little is known about the impacts of daylength extension due to outdoor lighting technologies on wild plant communities, despite the fact that plant growth and development are under photoperiodic control. In a five‐year field experiment, artificial ecosystems (“mesocosms”) of grassland communities both alone or in combination with invertebrate herbivores and predators were exposed to light treatments that simulated street lighting technologies (low‐pressure sodium, and light‐emitting diode [LED]‐based white lighting), at ground‐level illuminance. Most of the plant species in the mesocosms did not exhibit changes in biomass accumulation after 5 years of exposure to the light treatments. However, the white LED treatment had a significant negative effect on biomass production in the herbaceous species Lotus pedunculatus. Likewise, the interaction between the white LED treatment and the presence of herbivores significantly reduced the mean shoot/root ratio of the grass species Holcus lanatus. Artificial nighttime lighting had no effect on the foliar carbon or nitrogen in most of the grassland species. Nevertheless, the white LED treatment significantly increased the leaf nitrogen content in Lotus corniculatus in the presence of herbivores. Long‐term exposure to artificial light at night had no general effects on plant biomass responses in experimental grassland communities. However, species‐specific and negative effects of cool white LED lighting at ground‐level illuminance on biomass production and allocation in mixed plant communities are suggested by our findings. Further studies on the impacts of light pollution on biomass accumulation in plant communities are required as these effects could be mediated by different factors, including herbivory, competition, and soil nutrient availability.

Costs and benefits of "insect friendly" artificial lights are taxon specific

The expansion of human activity into natural habitats often results in the introduction of artificial light at night, which can disrupt local ecosystems. Recent advances in LED technology have enabled spectral tuning of artificial light sources, which could in theory limit their impact on vulnerable taxa. To date, however, experimental comparisons of ecologically friendly candidate colors have often considered only one type of behavioral impact, sometimes on only single species. Resulting recommendations cannot be broadly implemented if their consequences for other local taxa are unknown. Working at a popular firefly ecotourism site, we exposed the insect community to artificial illumination of three colors (blue, broad-spectrum amber, red) and measured flight-to-light behavior as well as the courtship flash behavior of male Photinus carolinus fireflies. Firefly courtship activity was greatest under blue and red lights, while the most flying insects were attracted to blue and broad-spectrum amber lights. Thus, while impacts of spectrally tuned artificial light varied across taxa, our results suggest that red light, rather than amber light, is least disruptive to insects overall, and therefore more generally insect friendly.

The Matthew effect: Common species become more common and rare ones become more rare in response to artificial light at night

Artificial light at night (ALAN) has been and still is rapidly spreading and has become an important component of global change. Although numerous studies have tested its potential biological and ecological impacts on animals, very few studies have tested whether it affects alien and native plants differently. Furthermore, common plant species, and particularly common alien species, are often found to benefit more from additional resources than rare native and rare alien species. Whether this is also the case with regard to increasing light due to ALAN is still unknown. Here, we tested how ALAN affected the performance of common and rare alien and native plant species in Germany directly, and indirectly via flying insects. We grew five common alien, six rare alien, five common native, and four rare native plant species under four combinations of two ALAN (no ALAN vs. ALAN) and two insect-exclusion (no exclusion vs. exclusion) treatments, and compared their biomass production. We found that common plant species, irrespective of their origin, produced significantly more biomass than rare species and that this was particularly true under ALAN. Furthermore, alien species tended to show a slightly stronger positive response to ALAN than native species did (p = .079). Our study shows that common plant species benefited more from ALAN than rare ones. This might lead to competitive exclusion of rare species, which could have cascading impacts on other trophic levels and thus have important community-wide consequences when ALAN becomes more widespread. In addition, the slightly more positive response of alien species indicates that ALAN might increase the risk of alien plant invasions.

Artificial light at night: an underappreciated effect on phenology of deciduous woody plants

Artificial light at night (ALAN), an increasing anthropogenic driver, is widespread and shows rapid expansion with potential adverse impact on the terrestrial ecosystem. However, whether and to what extent does ALAN affect plant phenology, a critical factor influencing the timing of terrestrial ecosystem processes, remains unexplored due to limited ALAN observation. Here, we used the Black Marble ALAN product and phenology observations from USA National Phenology Network to investigate the impact of ALAN on deciduous woody plants phenology in the conterminous United States. We found that (1) ALAN significantly advanced the date of breaking leaf buds by 8.9 ± 6.9 days (mean ± SD) and delayed the coloring of leaves by 6.0 ± 11.9 days on average; (2) the magnitude of phenological changes was significantly correlated with the intensity of ALAN (P < 0.001); and (3) there was an interaction between ALAN and temperature on the coloring of leaves, but not on breaking leaf buds. We further showed that under future climate warming scenarios, ALAN will accelerate the advance in breaking leaf buds but exert a more complex effect on the coloring of leaves. This study suggests intensified ALAN may have far-reaching but underappreciated consequences in disrupting key ecosystem functions and services, which requires an interdisciplinary approach to investigate. Developing lighting strategies that minimize the impact of ALAN on ecosystems, especially those embedded and surrounding major cities, is challenging but must be pursued.

A Systematic Review for Establishing Relevant Environmental Parameters for Urban Lighting: Translating Research into Practice

The application of lighting technologies developed in the 20th century has increased the brightness and changed the spectral composition of nocturnal night-time habitats and night skies across urban, peri-urban, rural, and pristine landscapes, and subsequently, researchers have observed the disturbance of biological rhythms of flora and fauna. To reduce these impacts, it is essential to translate relevant knowledge about the potential adverse effects of artificial light at night (ALAN) from research into applicable urban lighting practice. Therefore, the aim of this paper is to identify and report, via a systematic review, the effects of exposure to different physical properties of artificial light sources on various organism groups, including plants, arthropods, insects, spiders, fish, amphibians, reptiles, birds, and non-human mammals (including bats, rodents, and primates). PRISMA 2020 guidelines were used to identify a total of 1417 studies from Web of Science and PubMed. In 216 studies, diverse behavioral and physiological responses were observed across taxa when organisms were exposed to ALAN. The studies showed that the responses were dependent on high illuminance levels, duration of light exposure, and unnatural color spectra at night and also highlighted where research gaps remain in the domains of ALAN research and urban lighting practice. To avoid misinterpretation, and to define a common language, key terminologies and definitions connected to natural and artificial light have been provided. Furthermore, the adverse impacts of ALAN urgently need to be better researched, understood, and managed for the development of future lighting guidelines and standards to optimize sustainable design applications that preserve night-time environment(s) and their inhabiting flora and fauna.

11 Pressing Research Questions on How Light Pollution Affects Biodiversity

Artificial light at night (ALAN) is closely associated with modern societies and is rapidly increasing worldwide. A dynamically growing body of literature shows that ALAN poses a serious threat to all levels of biodiversity—from genes to ecosystems. Many “unknowns” remain to be addressed however, before we fully understand the impact of ALAN on biodiversity and can design effective mitigation measures. Here, we distilled the findings of a workshop on the effects of ALAN on biodiversity at the first World Biodiversity Forum in Davos attended by several major research groups in the field from across the globe. We argue that 11 pressing research questions have to be answered to find ways to reduce the impact of ALAN on biodiversity. The questions address fundamental knowledge gaps, ranging from basic challenges on how to standardize light measurements, through the multi-level impacts on biodiversity, to opportunities and challenges for more sustainable use.

Artificial Light at Night Impacts the Litter Layer Invertebrate Community With No Cascading Effects on Litter Breakdown

Artificial light at night (ALAN) can impact the trophic structure of assemblages of ground-dwelling invertebrates, and changes in such assemblages can affect decomposition in terrestrial systems due to the various functional roles of these invertebrates, including microbial grazing, comminution of litter, and predation of other invertebrates, that can directly or indirectly affect plant-litter breakdown. Despite this, we are unaware of any studies that have evaluated the effects of ALAN on the breakdown of plant litter in a terrestrial ecosystem. We sought to answer whether ALAN affects litter breakdown via its effects on a community of ground-dwelling arthropods using two field experiments. In one experiment, we manipulated the presence of ALAN and the size classes of soil invertebrates that could enter mesh bags containing plant litter (litterbags). We found that the rate of plant-litter breakdown increased with the mesh size of litterbags but was unaffected by presence of ALAN. In a second field experiment carried out to examine the effects of ALAN on the trophic structure of litter-layer invertebrate communities, while controlling for potential effects of ALAN on vegetation, we again found that ALAN did not affect litter breakdown despite the fact that ALAN increased the abundances of secondary and tertiary consumers. Our finding that larger assemblages of ground-dwelling secondary and tertiary consumer invertebrates under ALAN did not slow litter breakdown through increased top-down control of detritivores suggests ALAN may disrupt predator-prey interactions in litter-layer communities.

Artificial night light alters ecosystem services provided by biotic components

The global catastrophe of natural biodiversity and ecosystem services are expedited with the growing human population. Repercussions of artificial light at night ALAN are much wider, as it varies from unicellular to higher organism. Subsequently, hastened pollution and over exploitation of natural resources accelerate the expeditious transformation of climatic phenomenon and further cause global biodiversity losses. Moreover, it has a crucial role in global biodiversity and ecosystem services losses via influencing the ecosystem biodiversity by modulating abundance, number and aggregation at every levels as from individual to biome levels. Along with these affects, it disturbs the population, genetics and landscape structures by interfering inter- and intra-species interactions and landscape formation processes. Furthermore, alterations in normal light/dark (diurnal) signalling disrupt the stable physiological, biochemical, and molecular processes and modulate the regulating, cultural and provisioning ecosystem services and ultimately disorganize the stable ecosystem structure and functions. Moreover, ALAN reshapes the abiotic component of the ecosystem, and as a key component of global warming via producing greenhouse gases via emitting light. By taking together the above facts, this review highlights the impact of ALAN on the ecosystem and its living and non-living components, emphasizing to the terrestrial and aquatic ecosystem. Further, we summarize the means of minimizing strategies of ALAN in the environment, which are very crucial to reduce the further spread of night light contamination in the environment and can be useful to minimize the drastic impacts on the ecosystem.

Response of Vegetation Photosynthetic Phenology to Urbanization in Dongting Lake Basin, China

Urbanization can induce environmental changes such as the urban heat island effect, which in turn influence the terrestrial ecosystem. However, the effect of urbanization on the phenology of subtropical vegetation remains relatively unexplored. This study analyzed the changing trend of vegetation photosynthetic phenology in Dongting Lake basin, China, and its response to urbanization using nighttime light and chlorophyll fluorescence datasets. Our results indicated the start of the growing season (SOS) of vegetation in the study area was significantly advanced by 0.70 days per year, whereas the end of the growing season (EOS) was delayed by 0.24 days per year during 2000–2017. We found that urbanization promoted the SOS advance and EOS delay. With increasing urbanization intensity, the sensitivity of SOS to urbanization firstly increased then decreased, while the sensitivity of EOS to urbanization decreased with urbanization intensity. The climate sensitivity of vegetation phenology varied with urbanization intensity; urbanization induced an earlier SOS by increasing preseason minimum temperatures and a later EOS by increasing preseason precipitation. These findings improve our understanding of the vegetation phenology response to urbanization in subtropical regions and highlight the need to integrate human activities into future vegetation phenology models.

Streetlights positively affect the presence of an invasive grass species

Anthropogenic disturbances associated with urban ecosystems can create favorable conditions for populations of some invasive plant species. Light pollution is one of these disturbances, but how it affects the growth and establishment of invasive plant populations is unknown. Cheatgrass (Bromus tectorum) is a problematic invasive species where it has displaced native grassland communities in the United States, but to our knowledge, there have been no studies of the ecological factors that affect cheatgrass presence in urban ecosystems. We conducted field surveys in urban alleys in Denver, Colorado, to compare the presence of cheatgrass at sites with and without artificial light at night (hereafter artificial light) from streetlights. These streetlights are mounted on utility poles, which cause ground disturbance when installed in alleys; we were able to test the independent effect of poles on cheatgrass establishment because not all poles have streetlights on them. We found that cheatgrass was positively associated with the presence of streetlights and to a lesser extent poles. In addition to cheatgrass, we also found that other plants were positively associated with the presence of both poles and streetlights. Our results suggest that artificial light may benefit the occurrence of cheatgrass and other plant species in urban settings. While invasive populations of cheatgrass in wild habitats attract the most attention from managers, we suggest more consideration for this grass in urban environments where its growth and establishment benefit from anthropogenic changes.

Urban warming and artificial light alter dormancy in the flesh fly

Seasonal changes in temperature and day length are distinct between rural and urban areas due to urban warming and the presence of artificial light at night. Many studies have focused on the impacts of these ubiquitous signatures on daily biological events, but empirical studies on their impacts on insect seasonality are limited. In the present study, we used the flesh fly Sarcophaga similis as a model insect to determine the impacts of urbanization on the incidence and timing of diapause (dormancy), not only in the laboratory but also in rural and urban conditions. In the laboratory, diapause entry was affected by night-time light levels as low as 0.01 lux. We placed fly cages on outdoor shelves in urban and rural areas to determine the timing of diapause entry; it was retarded by approximately four weeks in urban areas relative to that in rural areas. Moreover, almost all flies in the site facing an urban residential area failed to enter diapause, even by late autumn. Although an autumnal low temperature in the urban area would mitigate the negative effect of artificial light at night, strong light pollution seriously disrupts the flesh fly seasonal adaptation.

Artificial light at night alters activity, body mass, and corticosterone level in a tropical anuran

Photoperiod is a major factor regulating biological rhythms in animals and plants. At low latitudes, annual variation in daylength is low and species are expected to strongly rely on photic cues to reset their circadian clocks. A corollary is that individuals should be strongly affected by sudden changes in the photic regime as those generated by artificial light at night (ALAN). We tested this hypothesis in an anuran in Costa Rica (10°N). Using an outdoor experimental design, we exposed adult cane toads Rhinella marina, a broadly distributed tropical anuran species to two ALAN intensities (0.04 and 5 lx). Locomotor activity was reduced at the lowest intensity, and the activity pattern shifted from crepuscular to nocturnal. Contrary to humans and mice in which ALAN favor obesity, toads from the two exposed groups did not gain mass whereas controls did. Corticosterone was reduced at the highest intensity, a possible consequence of the reduced activity of toads or the altered regulation of their circadian pattern. Thus, the behavioral and physiological disruption that we observed supports the hypothesis of the strong reliance on photic cues to regulate circadian rhythms and control homeostasis in this intertropical anuran. Furthermore, our results suggest that the negative effects of ALAN on physiology, in particular body mass regulation, may differ between vertebrate groups, thus preventing anticipated generalization before more comparative studies have been carried out. We stress the importance of considering the impact of the changing nocturnal environment in the intertropical zone which host the largest fraction of biodiversity.

Artificial light at night may increase the predation pressure in a salt marsh keystone species

Artificial light at night (ALAN) has the potential to alter ecological processes such as the natural dynamics of predator-prey interactions. Although understanding of ALAN effect on faunal groups has increased in recent years, few studies have explicitly tested for direct consequences of ALAN on predator-prey systems. Here, we evaluated the effect of ALAN on juvenile mortality due to cannibalism and general predation of the South American intertidal burrowing crab Neohelice granulata, a key ecosystem engineer of salt marshes. For this, we conducted tethering and crab enclosure experiments for both night and day periods during successive tidal floods in a semidiurnal tidal regime. Both experimental approaches were deployed simultaneously in the field and they lasted four consecutive days during new moon nights. ALAN was simulated by a white LED lamp (30W) with a solar panel as a source of power in five separated areas selected as replicates. For general predation, juvenile survival under ALAN was 44% lower than during the daytime and 61% lower than under natural dark conditions. For cannibalism, juvenile survival under ALAN and during the daytime was similar and about 30% lower than under natural dark conditions. We also found that the abundance of adult male crabs (cannibals) under ALAN was nearly five times higher than at natural dark conditions. Our field experiments provide evidence that ALAN can increase the mortality of juvenile crabs and is at least partially driven by cannibalistic interactions.

Light at Night and Disrupted Circadian Rhythms Alter Physiology and Behavior

Life on earth has evolved during the past several billion years under relatively bright days and dark nights. Virtually, all organisms on the planet display an internal representation of the solar days in the form of circadian rhythms driven by biological clocks. Nearly every aspect of physiology and behavior is mediated by these internal clocks. The widespread adoption of electric lights during the past century has exposed animals, including humans, to significant light at night for the first time in our evolutionary history. Importantly, endogenous circadian clocks depend on light for synchronization with the external daily environment. Thus, light at night can derange temporal adaptations. Indeed, disruption of natural light-dark cycles results in several physiological and behavioral changes. In this review, we highlight recent evidence demonstrating how light at night exposure can have serious implications for adaptive physiology and behavior, including immune, endocrine, and metabolic function, as well as reproductive, foraging, and migratory behavior. Lastly, strategies to mitigate the consequences of light at night on behavior and physiology will be considered.

Artificial light at night alters the seasonal responses of biting mosquitoes

Urban light pollution caused by artificial light at night (ALAN) profoundly affects the ecology, behavior, and physiology of plants and animals. Further, this widespread environmental pollutant has the potential to negatively impact human and animal health by changing the seasonal dynamics of disease-transmitting insects. In response to short days, females of the Northern house mosquito enter an overwintering dormancy, or diapause. While in diapause, female mosquitoes divert energy away from reproduction, cease blood-feeding, and no longer transmit disease. We demonstrate that exposure to dim ALAN (~4 lx) causes female mosquitoes to avert diapause and become reproductively active, as these females acquired less fat content, developed larger egg follicles, imbibed vertebrate blood, and produced viable eggs and larvae. Our findings suggest that mosquitoes in highly light-polluted areas such as cities may be actively reproducing and biting later in the season, thereby extending the period of disease risk for urban residents. Our results suggest that ALAN should be considered when modeling mosquito abundance, disease risk, and when deciding how long mosquito surveillance and control should persist in temperate regions.

Artificial Light at Night Advances Spring Phenology in the United States

Plant phenology is closely related to light availability as diurnal and seasonal cycles are essential environmental cues for organizing bio-ecological processes. The natural cycles of light, however, have been dramatically disrupted by artificial light at night (ALAN) due to recent urbanization. The influence on plant phenology of ALAN and its spatial variation remain largely unknown. By analyzing satellite data on ALAN intensity across the United States, here, we showed that ALAN tended to advance the start date of the growing season (SOS), although the overall response of SOS to ALAN was relatively weak compared with other potential factors (e.g., preseason temperature). The phenological impact of ALAN showed a spatially divergent pattern, whereby ALAN mainly advanced SOS at climatically moderate regions within the United States (e.g., Virginia), while its effect was insignificant or even reversed at very cold (e.g., Minnesota) and hot regions (e.g., Florida). Such a divergent pattern was mainly attributable to its high sensitivity to chilling insufficiency, where the advancing effect on SOS was only triggered on the premise that chilling days exceeded a certain threshold. Other mechanisms may also play a part, such as the interplay among chilling, forcing and photoperiod and the difference in species life strategies. Besides, urban areas and natural ecosystems were found to suffer from similar magnitudes of influence from ALAN, albeit with a much higher baseline ALAN intensity in urban areas. Our findings shed new light on the phenological impact of ALAN and its relation to space and other environmental cues, which is beneficial to a better understanding and projection of phenology changes under a warming and urbanizing future.

Very important dark sky areas in Europe and the Caucasus region

ALAN (artificial light at night) can give, if done adequately, a lot of benefits for human society, but it affects reproduction, navigation, foraging, habitat selection, communication, trophic and social interactions of the biota in the same time. Taking into account dramatic increase in light pollution of the night sky and night environment during the past decades, the creation of refugia where natural habitats are not influenced by ALAN is very important. We selected promising territories without, or with a low impact of, ALAN for the development of a VIDA (Very Important Dark Area) Network in Europe and the Caucasus region. 54 VIDAs within the borders of 30 countries were chosen, located in different biogeographic regions, at different altitudes, and in juxtaposition with protected areas. Special attention has been paid to sea and ocean islands, non-polluted by ALAN, as well as to large parts of European Russia and Kazakhstan where there is still a low level of light pollution. These places might be a basis for the protection of biodiversity from the consequences of ALAN, and they can also serve as key education centers for increasing the awareness of the problem of light pollution of the sky at night. Due to the fact that light propagates far away in the atmosphere, the protection of VIDAs can be obtained only if a strong anti-light pollution action is enforced also in the surrounding areas, at least 100 km from the borders of the VIDAs.

Effects of constant light exposure on sphingolipidomics and progression of NASH in high-fat-fed rats

BACKGROUND AND AIM

Non-alcoholic fatty liver disease (NAFLD) is a growing public health concern worldwide. With the progression of urbanization, light pollution is becoming an inevitable risk factor for NAFLD. However, the role of light pollution on NAFLD is insufficiently understood, and the underlying mechanism remains unclear. The present study explored effects of constant light exposure on NAFLD and elucidated its related mechanisms.

METHODS

Thirty-two male Sprague Dawley rats were divided into four groups (n = 8 each): (i) rats on a normal diet exposed to standard light-dark cycle (ND-LD); (ii) rats on a normal diet exposed to constant light (ND-LL); (iii) rats on a high-fat diet exposed to standard light-dark cycle (HFD-LD); and (iv) and rats on a high-fat diet exposed to constant light (HFD-LL). After 12 weeks of treatment, rats were sacrificed and pathophysiological assessments were performed. Targeted lipidomics was used to measure sphingolipids, including ceramides, glucosylceramides, and lactosylceramides, sphingomyelins, and sphingosine-1-phosphates in plasma and liver tissues.

RESULTS

In normal chow rats, constant light exposure led to glucose abnormalities and dyslipidemia. In high-fat-fed rats, constant light exposure exacerbated glucose abnormalities, dyslipidemia, insulin resistance, and inflammation and aggravated steatohepatitis. Compared with HFD-LD rats, HFD-LL had decreased plasma sphingosine-1-phosphate and elevated liver concentrations of total ceramide and specific ceramide species (ceramide d18:0/24:0, ceramide d18:1/22:0, ceramide d18:1/24:0, and ceramide d18:1/24:1), which were associated with increased hepatocyte apoptosis.

CONCLUSIONS

Constant light exposure causes dysregulation of sphingolipids and promotes steatohepatitis in high-fat-fed rats.

Reproduction under light pollution: maladaptive response to spatial variation in artificial light in a glow-worm

The amount of artificial light at night is growing worldwide, impacting the behaviour of nocturnal organisms. Yet, we know little about the consequences of these behavioural responses for individual fitness and population viability. We investigated if females of the common glow-worm Lampyris noctiluca—which glow in the night to attract males—mitigate negative effects of artificial light on mate attraction by adjusting the timing and location of glowing to spatial variation in light conditions. We found females do not move away from light when exposed to a gradient of artificial light, but delay or even refrain from glowing. Further, we demonstrate that this response is maladaptive, as our field study showed that staying still when exposed to artificial light from a simulated streetlight decreases mate attraction success, while moving only a short distance from the light source can markedly improve mate attraction. These results indicate that glow-worms are unable to respond to spatial variation in artificial light, which may be a factor in their global decline. Consequently, our results support the hypothesis that animals often lack adaptive behavioural responses to anthropogenic environmental changes and underlines the importance of considering behavioural responses when investigating the effects of human activities on wildlife.

Effects of artificial light at night on foraging behavior and vigilance in a nocturnal rodent

Artificial light at night has greatly changed the physical environment for many organisms on a global scale. As an energy efficient light resource, light emitting diodes (LEDs) have been widely used in recent years. As LEDs often have a broad spectrum, many biological processes may be potentially affected. In this study, we conducted manipulated experiments in rat-proof enclosures to explore the effects of LED night lighting on behavior of a nocturnal rodent, the Mongolian five-toed jerboa (Allactaga sibirica). We adopted the giving-up density (GUD) method and camera video trapping to study behavioral responses in terms of patch use, searching efficiency and vigilance. With the presence of white LED lighting, jerboas spent less time in patches, foraged less intensively (with higher GUDs) and became vigilant more frequently, while their searching efficiency was higher than under dark treatment. Although both positive and negative effects of LEDs on foraging were detected, the net effect of LEDs on jerboas is negative, which may further translate into changes in population dynamics, inter-specific interaction and community structure. To our knowledge, this is the first field study to explore how LED lighting affect foraging behavior and searching efficiency in rodents. Our results may have potential implications for practices such as pest control.

Interactions between artificial light at night, soil moisture, and plant density affect the growth of a perennial wildflower

Artificial light at night (ALAN) has been shown to alter aspects of plant growth, but we are not aware of any studies that have examined whether the effects of ALAN on plants depend upon the backdrop of variation in other abiotic factors that plants encounter in field populations. We conducted a field experiment to investigate whether ALAN affects the growth and anti-herbivore defenses of common milkweed, Asclepias syriaca, and whether the effects of ALAN are influenced by plant density or soil moisture content. Artificial light at night, soil moisture, and plant density were manipulated according to a split-plot factorial design. Although increasing soil moisture by watering had no significant effects on latex exudation, attributes of plant growth generally responded positively to watering. The basal stem diameter (BSD) and height of plants were affected by ALAN × soil moisture interactions. For both of these variables, the positive effects of ALAN were greater for plants that were not watered than for plants that were. Basal stem diameter was also affected by an ALAN × plant density interaction, and the positive effect of ALAN on BSD was greater in the low-density treatment than in the high-density treatment. Our results demonstrate that the effects of ALAN on plant growth can be altered by soil moisture and plant density. Consequently, the effects of ALAN on plants in nature may not be consistent with existing frameworks that do not account for critical abiotic variables such as water availability or biotic interactions between plants such as competition.

Effects of Artificial Light at Night (ALAN) on European Hedgehog Activity at Supplementary Feeding Stations

: Artificial light at night (ALAN) can have negative consequences for a wide range of taxa. However, the effects on nocturnal mammals other than bats are poorly understood. A citizen science camera trapping experiment was therefore used to assess the effect of ALAN on the activity of European hedgehogs (Erinaceus europaeus) at supplementary feeding stations in UK gardens. A crossover design was implemented at 33 gardens with two treatments-artificial light and darkness-each of which lasted for one week. The order of treatment depended on the existing lighting regime at the feeding station: dark treatments were applied first at dark feeding stations, whereas light treatments were used first where the station was already illuminated. Although temporal changes in activity patterns in response to the treatments were noted in some individuals, the direction of the effects was not consistent. Similarly, there was no overall impact of ALAN on the presence or feeding activities of hedgehogs in gardens where supplementary feeding stations were present. These findings are somewhat reassuring insofar as they demonstrate no net negative effect on a species thought to be in decline, in scenarios where the animals are already habituated to supplementary feeding. However, further research is needed to examine long-term effects and the effects of lighting on hedgehog prey, reproductive success and predation risk.

Optimization of Artificial Light for Spinach Growth in Plant Factory Based on Orthogonal Test

Artificial LED source provides the possibility to regulate the lighting environment in plant factorys that use limited space to plant, aiming at high throughput and good quality. However, different parameters of light intensity, quality, and photoperiod will influence the growth and accumulation of bio-compounds in plants. In order to find the optimal setting of LED light for spinach planting, four group experiments were designed using the orthogonal testing method. According to the experimental results, for growth indexes including fresh weight, dry weight, root length and so on, photoperiod is the most influential factor, light intensity is the second, and light quality is the least. The best light mode (R:B = 4:1, photosynthetic photon flux density (PPFD) = 100 μmol∙m⁻²∙s⁻¹ and 13/11 h) among all eight possible combinations in the range was also determined. Furthermore, for quality indexes, including the soluble sugar content, protein content and so on, a new scoring method was introduced to make a comprehensive score for evaluating. Then, the light combination (R:B = 4:1, PPFD = 150 μmol∙m⁻²∙s⁻¹ and 9/15 h) in the range was found as the optimal scheme for spinach quality under those parameters. As there is trade-off between the optimal light parameters for growth and quality, it is necessary to achieve a balance between yield and quality of the plant during production. If farmers want to harvest spinach with larger leaf area and higher yield, they need to pay attention to the adjustment of the photoperiod and use a lower light intensity and a longer lighting time. If they do not mind the yield of the vegetable but want to improve the taste and nutrition of spinach products, they should pay more attention to the light intensity and use a higher light intensity and a shorter lighting time.

Artificial Light Increases Local Predator Abundance, Predation Rates, and Herbivory

Human activity is rapidly increasing the radiance and geographic extent of artificial light at night (ALAN) leading to alterations in the development, behavior, and physiological state of many organisms. A limited number of community-scale studies investigating the effects of ALAN have allowed for spatial aggregation through positive phototaxis, the commonly observed phenomenon of arthropod movement toward light. We performed an open field study (without restricted arthropod access) to determine the effects of ALAN on local arthropod community composition, plant traits, and local herbivory and predation rates. We found strong positive phototaxis in 10 orders of arthropods, with increased (159% higher) overall arthropod abundance under ALAN compared to unlit controls. The arthropod community under ALAN was more diverse and contained a higher proportion of predaceous arthropods (15% vs 8%). Predation of immobilized flies occurred 3.6 times faster under ALAN; this effect was not observed during the day. Contrary to expectations, we also observed a 6% increase in herbivory under ALAN. Our results highlight the importance of open experimental field studies in determining community-level effects of ALAN.

Long-Term Comparison of Attraction of Flying Insects to Streetlights after the Transition from Traditional Light Sources to Light-Emitting Diodes in Urban and Peri-Urban Settings

Among the different light sources used for street lighting, light-emitting diodes (LEDs) are likely to dominate the world market in the coming years. At the same time, the spectral composition of nocturnal illumination is changing. Europe and many other areas worldwide have implemented bans on energy-inefficient lamps, such as the still very common mercury vapor lamps. However, the impact of artificial light on insects is mostly tested with light-traps or flight-intercept traps that are used for short periods only. By comparing the numbers of insects attracted by street lamps before and after replacing mercury vapor light sources (MV) with light emitting diodes, we assessed the impact in more typical (urban and peri-urban) settings over several years. We found that LED attracted approximately half of the number of insects compared to MV lights. Furthermore, most insect groups are less drawn by LED than by MV, while Hymenoptera are less attracted by MV than by LED. Thus, the composition of the attracted communities differed between the light sources, which may impact ecosystem processes and functions. In green peri-urban settings more insects are attracted than in an urban setting, but the relative difference between the light sources is the same.

Users’ Awareness, Attitudes, and Perceptions of Health Risks Associated with Excessive Lighting in Night Markets: Policy Implications for Sustainable Development

The introduction of artificial lighting has dramatically transformed nighttime activities, becoming a very positive but also disruptive factor that must be optimized and adapted according to the guidelines of sustainable policies. In this framework, night markets in Thailand are definitely popular destinations among locals and tourists that are found in every town and city in the whole country, being the source of livelihoods for many people. It is well-known that shops in night markets frequently use colorful light sources, emitting high levels of illumination to attract customers. Since previous research has shown environmental risks of inappropriate lighting on human health and well-being, as well as on ecosystems, excessive lighting in night markets could have adverse effects on vendors’ health if they are exposed to high illumination levels during long hours every night. This is a risk for people, but also for their attachment to their lands, traditions, culture, and way of life. This study was designed to explore whether excessive illumination of night markets has impacts on vendors’ health and well-being. The research was conducted through an empirical study in a night market in the center of Surin province (Thailand), using observations and a questionnaire survey of 205 vendors and clients (non-vendors). The results show that night markets’ vendors were more likely to suffer from eye- and sleep-related problems than non-vendors. Women were affected more than men. The results also revealed that the majority of both vendors and non-vendors tended to have awareness about excessive lighting impacts on human health, with more vendors tending to agree with the fact than non-vendors. Although night markets’ are their main source of income, the majority of vendors were more unlikely to agree about the contribution of night markets to local livelihoods and development than non-vendors. These findings have implications for the Thai Authority in setting up appropriate lighting policies and regulations for night markets. The target is not only energy savings, but also to protect the public’s health, culture, and traditional livelihoods, in a way that supports sustainable development.

Artificial light pollution at night (ALAN) disrupts the distribution and circadian rhythm of a sandy beach isopod

Coastal habitats, in particular sandy beaches, are becoming increasingly exposed to artificial light pollution at night (ALAN). Yet, only a few studies have this far assessed the effects of ALAN on the species inhabiting these ecosystems. In this study we assessed the effects of ALAN on Tylos spinulosus, a prominent wrack-consumer isopod living in sandy beaches of north-central Chile. This species burrows in the sand during daylight and emerges at night to migrate down-shore, so we argue it can be used as a model species for the study of ALAN effects on coastal nocturnal species. We assessed whether ALAN alters the distribution and locomotor activity of this isopod using a light system placed in upper shore sediments close to the edge of the dunes, mimicking light intensities measured near public lighting. The response of the isopods was compared to control transects located farther away and not exposed to artificial light. In parallel, we measured the isopods' locomotor activity in the laboratory using actographs that recorded their movement within mesocosms simulating the beach surface. Measurements in the field indicated a clear reduction in isopod abundance near the source of the light and a restriction of their tidal distribution range, as compared to control transects. Meanwhile, the laboratory experiments showed that in mesocosms exposed to ALAN, isopods exhibited reduced activity and a circadian rhythm that was altered and even lost after a few days. Such changes with respect to control mesocosms with a natural day/night cycle suggest that the changes observed in the field were directly related to a disruption in the locomotor activity of the isopods. All together these results provide causal evidence of negative ALAN effects on this species, and call for further research on other nocturnal sandy beach species that might become increasingly affected by ALAN.

Artificial Light at Night Alleviates the Negative Effect of Pb on Freshwater Ecosystems

Artificial light at night (ALAN) is an increasing phenomenon worldwide that can cause a series of biological and ecological effects, yet little is known about its potential interaction with other stressors in aquatic ecosystems. Here, we tested whether the impact of lead (Pb) on litter decomposition was altered by ALAN exposure using an indoor microcosm experiment. The results showed that ALAN exposure alone significantly increased leaf litter decomposition, decreased the lignin content of leaf litter, and altered fungal community composition and structure. The decomposition rate was 51% higher in Pb with ALAN exposure treatments than in Pb without ALAN treatments, resulting in increased microbial biomass, β-glucosidase (β-G) activity, and the enhanced correlation between β-G and litter decomposition rate. These results indicate that the negative effect of Pb on leaf litter decomposition in aquatic ecosystems may be alleviated by ALAN. In addition, ALAN exposure also alters the correlation among fungi associated with leaf litter decomposition. In summary, this study expands our understanding of Pb toxicity on litter decomposition in freshwater ecosystems and highlights the importance of considering ALAN when assessing environmental metal pollutions.

Effects of artificial light on flowering of foredune vegetation

The impact of ecological light pollution involves alteration of periods of natural light, a fact that has proven effects on ecosystems. Few studies have focused on the impact of this pollution on wild plant species, and none on coastal dune plants. Many coastal dunes and their plants are adjacent to tourist areas, and these might be affected by light pollution. Such is the case of the Natural Reserve Dunas de Maspalomas (Gran Canaria), where some individuals of the plant species Traganum moquinii, located in the El Inglés beach foredune zone, are affected by light pollution. This study examines the effect of light pollution on the flowering process and, by extension, the reproductive cycle of these plants. Plants located closer to high artificial illumination sources receive ~2,120 h/yr of intense light more than plants located furthest from those artificial lighting sources. Parts of the plants of Traganum moquinii exposed directly to the artificial light show a significant decrease in the production of flowers, compared to the parts in plants in shade, and to the plants more distant from artificial lights. In consequence, plants exposed more directly to artificial light have a lower potential for seed reproduction. The spectrum of artificial light also affects the plants, and light between 600 and 700 nm primarily affects the reproductive cycle of the Traganum moquinii species. The implications for the ecological and geomorphological functioning of the dune system are discussed, because this species plays a decisive role in the formation of foredune zones and nebkhas in arid dune systems.

Artificial lighting at night alters aquatic-riparian invertebrate food webs

Artificial lighting at night (ALAN) is a global phenomenon that can be detrimental to organisms at individual and population levels, yet potential consequences for communities and ecosystem functions are less resolved. Riparian systems may be particularly vulnerable to ALAN. We investigated the impacts of ALAN on invertebrate community composition and food web characteristics for linked aquatic-terrestrial ecosystems. We focused on food chain length (FCL), a central property of ecological communities that can influence their structure, function, and stability; and the contribution of aquatically derived energy (i.e., nutritional subsidies originating from stream periphyton). We collected terrestrial arthropods and emergent aquatic insects from a suite of stream and wetland sites in Columbus, Ohio, USA. Stable isotopes of carbon (¹³ C) and nitrogen (¹⁵ N) were used to infer FCL and contribution of aquatically derived energy. We found that moderate-to-high levels of ALAN altered invertebrate community composition, favoring primarily predators and detritivores. Impacts of ALAN, however, were very taxon specific as illustrated, for example, by the negative impact of ALAN on the abundance of orb-web spiders belonging to the families Tetragnathidae and Araneidae: key invertebrate riparian predators. Most notably, we observed decreases in both invertebrate FCL and reliance on aquatically derived energy under ALAN (although aquatic energetic contributions appeared to increase again at higher levels of ALAN), in addition to shifts in the timing of reciprocal nutritional subsidies. Our study demonstrates that ALAN can alter the flows of energy between aquatic and terrestrial systems, thereby representing an environmental perturbation that can cross ecosystem boundaries. Given projections for global increases in ALAN, both in terms of coverage and intensity, these results have broad implications for stream ecosystem structure and function.

Nature, extent and ecological implications of night-time light from road vehicles

The erosion of night‐time by the introduction of artificial lighting constitutes a profound pressure on the natural environment. It has altered what had for millennia been reliable signals from natural light cycles used for regulating a host of biological processes, with impacts ranging from changes in gene expression to ecosystem processes.

Studies of these impacts have focused almost exclusively on those resulting from stationary sources of light emissions, and particularly streetlights. However, mobile sources, especially road vehicle headlights, contribute substantial additional emissions.

The ecological impacts of light emissions from vehicle headlights are likely to be especially high because these are (1) focused so as to light roadsides at higher intensities than commonly experienced from other sources, and well above activation thresholds for many biological processes; (2) projected largely in a horizontal plane and thus can carry over long distances; (3) introduced into much larger areas of the landscape than experience street lighting; (4) typically broad “white” spectrum, which substantially overlaps the action spectra of many biological processes and (5) often experienced at roadsides as series of pulses of light (produced by passage of vehicles), a dynamic known to have major biological impacts.

The ecological impacts of road vehicle headlights will markedly increase with projected global growth in numbers of vehicles and the road network, increasing the local severity of emissions (because vehicle numbers are increasing faster than growth in the road network) and introducing emissions into areas from which they were previously absent. The effects will be further exacerbated by technological developments that are increasing the intensity of headlight emissions and the amounts of blue light in emission spectra.

Synthesis and applications. Emissions from vehicle headlights need to be considered as a major, and growing, source of ecological impacts of artificial night‐time lighting. It will be a significant challenge to minimise these impacts whilst balancing drivers' needs at night and avoiding risk and discomfort for other road users. Nonetheless, there is potential to identify solutions to these conflicts, both through the design of headlights and that of roads.

Emissions from vehicle headlights need to be considered as a major, and growing, source of ecological impacts of artificial night‐time lighting. It will be a significant challenge to minimise these impacts whilst balancing drivers' needs at night and avoiding risk and discomfort for other road users. Nonetheless, there is potential to identify solutions to these conflicts, both through the design of headlights and that of roads.