Artificial light at night can modify ecosystem functioning beyond the lit area

Abstract

Artificial light at night (ALAN) is a relatively new and rapidly increasing global change driver. While evidence on adverse effects of ALAN for biodiversity and ecosystem functioning is increasing, little is known on the spatial extent of its effects. We therefore tested whether ALAN can affect ecosystem functioning in areas adjacent to directly illuminated areas. We exposed two phytometer species to three different treatments of ALAN (sites directly illuminated, sites adjacent to directly illuminated sites, control sites without illumination), and we measured its effect on the reproductive output of both plant species. Furthermore, in one of the two plant species, we quantified pre-dispersal seed predation and the resulting relative reproductive output. Finally, under controlled condition in the laboratory, we assessed flower visitation and oviposition of the main seed predator in relation to light intensity. There was a trend for reduced reproductive output of one of the two plant species on directly illuminated sites, but not of the other. Compared to dark control sites, seed predation was significantly increased on dark sites adjacent to illuminated sites, which resulted in a significantly reduced relative reproductive output. Finally, in the laboratory, the main seed predator flew away from the light source to interact with its host plant in the darkest area available, which might explain the results found in the field. We conclude that ALAN can also affect ecosystem functioning in areas not directly illuminated, thereby having ecological consequences at a much larger scale than previously thought. Artificial light at night (ALAN) is a relatively new global change driver, which is worldwide rapidly increasing 1. It has various ecological consequences as it can cause alterations in physiology and behaviour of organisms, thereby increasing mortality, reducing reproduction as well as altering species abundances and community composition 1-5. For example, many animals have been shown to be attracted 6,7 or repelled 8-11 by light. There is increasing evidence that ALAN has also consequences for species interactions: ALAN has been shown to alter mutualistic interactions, for example to disrupt nocturnal plant-pollinator interactions with negative consequences for the pollination service the nocturnal pollinators provide to the plants 12. However, most of the research so far has focused on the effect of ALAN on predation. 8,11,13-16. These studies show that ALAN can reduce or increase species interactions and ecosystem functioning, and that the effect often depends on light quality and quantity 5,17. However, so far, research has mostly focused on the impact ALAN has on species interactions and ecosystem functioning in directly illuminated areas 5,12,18,19 , ignoring what happens in areas in the surroundings of the illuminated area. Yet animals such as moths, might be attracted from long distances to the illuminated area potentially leading to lowered densities, interaction frequencies and ecosystem functioning in ...

Pollination and fruit infestation under artificial light at night:light colour matters

“…These results may be explained from the way light is affecting the behaviour of H. bicruris, which is not only a fruit predator but also the main pollinator. Females of H. bicruris show no fatal attraction to light at short distances 21 and hence it may be attracted to these light sources from longer distances, but at closer distances ‘escapes’ from this attraction. Thus, after being attracted over longer distances and leading to a higher density close to the lamp, there were more females to infest the flowers resulting in higher infestation rates under white and green light compared to the dark control.…”

“…Furthermore, artificial light at night might affect nocturnal pollinators and the pollination service they provide by altering their feeding and mating behaviour 19 , 20 . Artificial light can disrupt flight to mating and feeding locations 17 , 21 , and can distort the male response to pheromone as well as supress pheromone release of females 22 – 24 .…”

“…Thus, H. bicruris is both a pollinator and a herbivore for S. latifolia . It recently has been shown that the number of laid eggs in the flowers of S. latifolia is increased in areas adjacent to artificially illuminated areas but not in areas directly illuminated, most likely due to the fact that females of H. bicruris are able to fly away from artificial light sources and prefer dark oviposition sites 21 . Pollination of S. latifolia on the other hand seems not to be affected by light 21 .…”

“…It recently has been shown that the number of laid eggs in the flowers of S. latifolia is increased in areas adjacent to artificially illuminated areas but not in areas directly illuminated, most likely due to the fact that females of H. bicruris are able to fly away from artificial light sources and prefer dark oviposition sites 21 . Pollination of S. latifolia on the other hand seems not to be affected by light 21 . The study, however, focused on white light only, and we currently do not know whether the effect of light on the S. latifolia – H. bicruris relationship vary depending on the light colour.…”

“…Attraction to specific light colours might also invoke a difference in abundance among H. bicruris resulting in consequences for pollination, infestation rates and related seed predation. Alternatively, H. bicruris might avoid illuminated flowers for oviposition, thereby increasing infestation rates and seed predation in dark areas adjacent to light sources 21 .…”