Artificial night light alters nocturnal prey interception outcomes for morphologically variable spiders

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'.

Artificial light at night and anthropogenic noise alter the foraging activity and structure of vertebrate communities

Light and noise pollution from human activity are increasing at a dramatic rate. These sensory stimuli can have a wide range of effects on animal behavior, reproductive success, and physiology. However, less is known about the functional and community-level consequences of these sensory pollutants, especially when they co-occur. Using camera traps in a manipulative field experiment, we studied the effects of anthropogenic light and noise, singularly and in tandem, on richness and community turnover at both the taxa and functional group level as well as foraging activity. We showed that both light and noise pollution did alter taxonomic richness and that these effects can differ depending on the scale of observation. Increases in light levels had a negative effect on richness at the camera-level scale, but light-treated sites had the highest pooled (i.e., cumulative) richness of all treatment types. In contrast, noise was found to have a negative effect on cumulative richness; however, when both stimuli were present, the addition of night-lighting mitigated the effects of noise. Artificial light and moonlight had the strongest influence on community turnover, and results remained consistent at both the taxa and functional group level. Additionally, increases in ambient noise and moonlight, but not artificial light, reduced foraging activity. Our study provides evidence that alterations to the sensory environment can alter the richness and composition of communities and that effects can be scale-dependent and also alter foraging behavior. Unexpectedly, the addition of artificial light may have mitigated the negative effects of noise on cumulative taxonomic richness. This highlights the importance of researching the consequences of co-exposure to these globally common pollutants.

Artificial light at night disrupts species interactions and changes insect communities

Artificial light at night (ALAN) is globally increasing, posing a threat to biodiversity. The impact of nocturnal illumination on individual insects has been relatively well documented. Recent studies show that ALAN also impacts species interactions, including intra-specific communication, trophic interactions and plant-pollinator interactions, with cascading effects in the ecosystem and impacts on ecosystem functioning that extend beyond nocturnal communities and illuminated areas. Reduced population sizes and changes in community composition because of exposure to ALAN have been reported but the understanding of the impacts of ALAN on insect communities is currently limited to few groups and ecosystems. The theoretical framework on how ALAN impacts insect communities and populations is poorly developed, limiting our understanding and the formulation of relevant hypotheses.

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.

Artificial light at night alters the settlement of acorn barnacles on a man-made habitat in Atlantic Canada

Human growth has caused an unprecedented increase in artificial light at night (ALAN). In coastal habitats, many species rely on day/night cycles to regulate various aspects of their life history and these cycles can be altered by this stressor. This study assessed the influence of ALAN on the early (cyprid) and late (spat) settlement stages of the acorn barnacle Semibalanus balanoides, a species widely distributed in natural and man-made coastal habitats of the North Atlantic. A newly designed settlement plate, originally for studies in rocky intertidal habitats in the southeast Pacific, was adapted to measure settlement rates on man-made habitats -wharf seawalls- located in Atlantic Canada. Plates equipped with a small LED diode powered by an internal battery (ALAN plates) were used to quantify settlement rates in comparison to plates lacking a light source (controls). These plates were deployed for 6 d in the mid-intertidal levels, where adult barnacles were readily visible. ALAN and control plates collected large number of settlers and showed to be suitable for this type of man-made habitats. The number of early settlers (cyprids) did not differ between plates but the number of late settlers (spat) was significantly lower in ALAN plates than in controls. These results suggest that light pollution has little influence on the early stages of the acorn barnacle settlement but is clearly detrimental to its late stages. As barnacles dominate in many natural and man-made hard substrates, it is likely that ALAN also has indirect effects on community structure.

Exposure to artificial light at night during the larval stage has delayed effects on juvenile corticosterone concentration in American toads, Anaxyrus americanus

Artificial Light At Night (ALAN) is an environmental stressor that can disrupt individual physiology and ecological interactions. Hormones such as corticosterone are often responsible for mediating an organism's response to environmental stressors. We investigated whether ALAN was associated with a corticosterone response and whether it exacerbated the effects of another common stressor, predation. We tested for consumptive, non-consumptive, and physiological effects of ALAN and predator presence (dragonfly larvae) on a widespread amphibian, the American toad (Anaxyrus americanus). We found predators had consumptive (decreased survival) and non-consumptive (decreased growth) effects on larval toads. ALAN did not affect larval toads nor did it interact with the predator treatment to increase larval toad predation. Despite the consumptive and non-consumptive effects of predators, neither predators nor ALAN affected corticosterone concentration in the larval and metamorph life-stages. In contrast to studies in other organisms, we did not find any evidence that suggested ALAN alters predator-prey interactions between dragonfly larvae and toads. However, there was an inverse relationship between corticosterone and survival that was exacerbated by exposure to ALAN when predators were absent. Additionally, larval-stage exposure to ALAN increased corticosterone concentration in juvenile toads. Our results suggest the physiological effects of ALAN may not be demonstrated until later life-stages.

Orb-weaving spiders are fewer but larger and catch more prey in lit bridge panels from a natural artificial light experiment

Artificial light at night is rapidly changing the sensory world. While evidence is accumulating for how insects are affected, it is not clear how this impacts higher trophic levels that feed on insect communities. Spiders are important insect predators that have recently been shown to have increased abundance in urban areas, but have shown mixed responses to artificial light. On a single bridge with alternating artificially lit and unlit sections, I measured changes in the orb-weaving spider Larinioides sclopetarius (Araneidae) web abundance, web-building behavior, prey-capture, and body condition. In artificially lit conditions, spiders caught more prey with smaller webs, and had higher body conditions. However, there were fewer spiders with active webs in those lit areas. This suggests that either spiders were not taking advantage of an ecological insect trap, perhaps due to an increased risk of becoming prey themselves, or were satiated, and thus not as active within these habitats. The results from this natural experiment may have important consequences for both insects and spiders in urban areas under artificial lighting conditions.

Why conservation biology can benefit from sensory ecology

Global expansion of human activities is associated with the introduction of novel stimuli, such as anthropogenic noise, artificial lights and chemical agents. Progress in documenting the ecological effects of sensory pollutants is weakened by sparse knowledge of the mechanisms underlying these effects. This severely limits our capacity to devise mitigation measures. Here, we integrate knowledge of animal sensory ecology, physiology and life history to articulate three perceptual mechanisms-masking, distracting and misleading-that clearly explain how and why anthropogenic sensory pollutants impact organisms. We then link these three mechanisms to ecological consequences and discuss their implications for conservation. We argue that this framework can reveal the presence of 'sensory danger zones', hotspots of conservation concern where sensory pollutants overlap in space and time with an organism's activity, and foster development of strategic interventions to mitigate the impact of sensory pollutants. Future research that applies this framework will provide critical insight to preserve the natural sensory world.

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.

Illuminating the physiological implications of artificial light on an insectivorous bat community

Global light pollution threatens to disturb numerous wildlife species, but impacts of artificial light will likely vary among species within a community. Thus, artificial lights may change the environment in such a way as to create winners and losers as some species benefit while others do not. Insectivorous bats are nocturnal and a good model to test for differential effects of light pollution on a single community. We used a physiological technique to address this community-level question by measuring plasma ß-hydroxybutyrate (a blood metabolite) concentrations from six species of insectivorous bats in lit and unlit conditions. We also recorded bat calls acoustically to measure activity levels between experimental conditions. Blood metabolite level and acoustic activity data suggest species-specific changes in foraging around lights. In red bats (Lasiurus borealis), ß-hydroxybutyrate levels at lit sites were highest early in the night before decreasing. Acoustic data indicate pronounced peaks in activity at lit sites early in the night. In red bats on dark nights and in the other species in this community, which seem to avoid lights, ß-hydroxybutyrate remained relatively constant. Our results suggest red bats are more willing to expend energy to actively forage around lights despite potential negative impacts, while other, generally rarer species avoid lit areas. Artificial light appears to have a bifurcating effect on bat communities, whereby some species take advantage of concentrated prey resources, yet most do not. Further, this may concentrate light-intolerant species into limited dark refugia, thereby increasing competition for depauperate, phototactic insect communities.

The impact of artificial light at night on nocturnal insects: A review and synthesis

In recent decades, advances in lighting technology have precipitated exponential increases in night sky brightness worldwide, raising concerns in the scientific community about the impact of artificial light at night (ALAN) on crepuscular and nocturnal biodiversity. Long-term records show that insect abundance has declined significantly over this time, with worrying implications for terrestrial ecosystems. The majority of investigations into the vulnerability of nocturnal insects to artificial light have focused on the flight-to-light behavior exhibited by select insect families. However, ALAN can affect insects in other ways as well. This review proposes five categories of ALAN impact on nocturnal insects, highlighting past research and identifying key knowledge gaps. We conclude with a summary of relevant literature on bioluminescent fireflies, which emphasizes the unique vulnerability of terrestrial light-based communication systems to artificial illumination. Comprehensive understanding of the ecological impacts of ALAN on diverse nocturnal insect taxa will enable researchers to seek out methods whereby fireflies, moths, and other essential members of the nocturnal ecosystem can coexist with humans on an increasingly urbanized planet.

Artificial light at night alters life history in a nocturnal orb-web spider

The prevalence of artificial light at night (ALAN) is increasing rapidly around the world. The potential physiological costs of this night lighting are often evident in life history shifts. We investigated the effects of chronic night-time exposure to ecologically relevant levels of LED lighting on the life history traits of the nocturnal Australian garden orb-web spider (Eriophora biapicata). We reared spiders under a 12-h day and either a 12-h natural darkness (∼0 lux) or a 12-h dim light (∼20 lux) night and assessed juvenile development, growth and mortality, and adult reproductive success and survival. We found that exposure to ALAN accelerated juvenile development, resulting in spiders progressing through fewer moults, and maturing earlier and at a smaller size. There was a significant increase in daily juvenile mortality for spiders reared under 20 lux, but the earlier maturation resulted in a comparable number of 0 lux and 20 lux spiders reaching maturity. Exposure to ALAN also considerably reduced the number of eggs produced by females, and this was largely associated with ALAN-induced reductions in body size. Despite previous observations of increased fitness for some orb-web spiders in urban areas and near night lighting, it appears that exposure to artificial night lighting may lead to considerable developmental costs. Future research will need to consider the detrimental effects of ALAN combined with foraging benefits when studying nocturnal insectivores that forage around artificial lights.