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Maggi, E., Bongiorni, L., Fontanini, D., Capocchi, A., Dal Bello, M., Giacomelli, A., et al. (2019). Artificial light at night erases positive interactions across trophic levels. Funct Ecol, in press, 1365–2435.13485.
Abstract: Artificial light at night (ALAN) is one of the most recently recognized sources of anthropogenic disturbance, with potentially severe effects on biological systems that are still to be fully explored. Among marine ecosystems, high shore habitats are those more likely to be impacted by ALAN, due to a more intense exposition to outdoor nocturnal lightings (mostly from lamps along coastal streets and promenades, or within harbors, ports and marinas).
2.By performing in situ nocturnal manipulations of a direct source of white LED light and presence of herbivores in a Mediterranean high‐shore habitat, we assessed the interactive effects of light pollution and grazing on two key functional components of the epilithic microbial community (the cyanobacteria, as the main photoautotrophic component, and the other bacteria, mainly dominated by heterotrophs) developing on rocky shores.
3.Results showed an unexpected increase in the diversity of epilithic bacterial biofilm at unlit sites in the presence of grazers, that was more evident on the other (mainly heterotrophic) bacterial component, when giving weight to more abundant families. This effect was likely related to the mechanical removal of dead cells through the grazing activity of consumers. ALAN significantly modified this scenario, by reducing the density of grazers and thus erasing their effects on bacteria, and by increasing the diversity of more abundant cyanobacterial families.
4.Overall, direct and indirect effects on ALAN resulted in a significant increase in the diversity of the photoautotrophic component and a decrease in the heterotrophic one, likely affecting key ecosystem functions acting on rocky shore habitats.
5.ALAN may represent a threat for natural systems through the annihilation of positive interactions across trophic levels, potentially impairing the relationship between biodiversity and functioning of ecosystems and interacting with other global and local stressors currently impinging on coastal areas.
Secondi, J., Davranche, A., Théry, M., Mondy, N., Lengagne, T., & Isaac, N. (2019). Assessing the effects of artificial light at night on biodiversity across latitude – Current knowledge gaps. Global Ecol Biogeogr, in press, geb.13037.
Exposure to artificial light at night (ALAN) is a risk factor for organisms. Considering the spread and increasing intensity of night brightness across the globe, and the key role of light at all biological levels, alterations of ecosystems are expected. Yet, we cannot predict the severity of the effects of ALAN in several biomes because little information is available outside the temperate zone. We reviewed current knowledge and identified traits that could be targeted to fill this knowledge gap in order to contribute to the elaboration of a biogeographical framework for the study of ALAN at the global scale.
Current and next decades.
We analysed the latitudinal variation in ALAN and focused on environmental factors that vary with latitude but that have been overlooked. We reviewed biological traits that exhibit latitudinal variation and depend on light and photoperiod and compiled information about the predicted changes in human demography and road networks across different world regions.
Cloud cover amplifies ALAN far away from urbanized areas. Because of the higher frequency of overcast sky nights, exposure effects may be stronger both at high latitudes and across a large fraction of the intertropical zone, although at different times of the year. Intertropical biomes host the largest fraction of global biodiversity. Although currently they are not the most exposed to ALAN, their human populations are growing, and urbanized areas and road networks are expanding. Hence, ALAN could have strong ecological consequences, with cloud cover as an aggravating factor.
Knowledge gaps currently limit our ability to predict the effects of ALAN in different biomes. Therefore, it will be important to start investigating the consequences of this novel environmental factor across the globe, in order to develop a relevant theoretical framework.
Zachary M. Cravens, V. A. B., Timothy J. Divoll, Justin G. Boyles. (2018). Illuminating prey selection in an insectivorous bat community, exposed to artificial light at night. Journal of Applied Ecology, 55(2), 705–713.
Abstract: 1.Light pollution has been increasing around the globe and threatens to disturb natural rhythms of wildlife species. Artificial light impacts the behaviour of insectivorous bats in numerous ways, including foraging behaviour, which may in turn lead to altered prey selection.
2.In a manipulative field experiment, we collected faecal samples from six species of insectivorous bats in naturally dark and artificially lit conditions, and identified prey items using molecular methods to investigate effects of light pollution on prey selection.
3.Proportional differences of identified prey were not consistent and appeared to be species specific. Red bats, little brown bats, and gray bats exhibited expected increases in moths at lit sites. Beetle-specialist big brown bats had a sizeable increase in beetle consumption around lights, while tri-colored bats and evening bats showed little change in moth consumption between experimental conditions. Dietary overlap was high between experimental conditions within each species, and dietary breadth only changed significantly between experimental conditions in one species, the little brown bat.
4.Policy implications. Our results, building on others, demonstrate that bat-insect interactions may be more nuanced than the common assertion that moth consumption increases around lights. They highlight the need for a greater mechanistic understanding of bat-light interactions to predict which species will be most affected by light pollution. Given differences in bat and insect communities, we advocate biologists, land stewards, and civil planners work collaboratively to determine lighting solutions that minimize changes in foraging behaviour of species in the local bat community. Such efforts may allow stakeholders to more effectively craft management strategies to minimize unnatural shifts in prey selection caused by artificial lights.
Gaston, K. J., & Holt, L. A. (2018). Nature, extent and ecological implications of night‐time light from road vehicles. Journal of Applied Ecology, 55(5), 2296–2307.
Abstract: 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.
Cruz, L. M., Shillinger, G. L., Robinson, N. J., Tomillo, P. S., & Paladino, F. V. (2018). Effect of light intensity and wavelength on the in-water orientation of olive ridley turtle hatchlings. Journal of Experimental Marine Biology and Ecology, 505, 52–56.
Abstract: Light pollution, associated with coastal development, poses a growing threat to sea turtles. Hatchlings are particularly affected during their crawl to the ocean since they exhibit phototaxis and may move towards or be disoriented by artificial lights. Although much is known about how hatchlings respond to artificial light while crawling to the ocean, far less is known about their response after reaching the water. Here, we investigate how hatchling olive ridley turtles (Lepidochelys olivacea) held in artificial pools responded to light of different wavelengths (red, 720 nm; yellow, 660 nm and green, 520 nm) and intensities (0.1–3.3 lx, mean 0.87 lx, SD = 0.85, 10.3–45.9 lx, mean 15.75 lx,SD = 7.12; 47.5–84.2 lx; mean 52.02 lx, SD = 9.11; 91.3–140.8 lx, mean 105 lx, SD = 13.24; 150.1–623 lx, mean 172.18 lx, SD = 73.42). When no light or red light below 39 lx was present, hatchlings oriented at a mean angle of 180° from true north and did not orient towards any discernable feature. However, hatchlings swam towards the light at intensities of red light above 39 lx, yellow light above 10 lx and green light above 5 lx. Our findings indicate that sea turtles will swim towards artificial lights even after reaching the water. Thus, we recommend light mitigation efforts should extend beyond nesting beaches and into the associated oceanic habitats.