Experimental illumination of natural habitat—an experimental set-up to assess the direct and indirect ecological consequences of artificial light of different spectral composition

Abstract

Artificial night-time illumination of natural habitats has increased dramatically over the past few decades. Generally, studies that assess the impact of artificial light on various species in the wild make use of existing illumination and are therefore correlative. Moreover, studies mostly focus on short-term consequences at the individual level, rather than long-term consequences at the population and community level—thereby ignoring possible unknown cascading effects in ecosystems. The recent change to LED lighting has opened up the exciting possibility to use light with a custom spectral composition, thereby potentially reducing the negative impact of artificial light. We describe here a large-scale, ecosystem-wide study where we experimentally illuminate forest-edge habitat with different spectral composition, replicated eight times. Monitoring of species is being performed according to rigid protocols, in part using a citizen-science-based approach, and automated where possible. Simultaneously, we specifically look at alterations in behaviour, such as changes in activity, and daily and seasonal timing. In our set-up, we have so far observed that experimental lights facilitate foraging activity of pipistrelle bats, suppress activity of wood mice and have effects on birds at the community level, which vary with spectral composition. Thus far, we have not observed effects on moth populations, but these and many other effects may surface only after a longer period of time.

Out of the Dark: Establishing a Large-Scale Field Experiment to Assess the Effects of Artificial Light at Night on Species and Food Webs

“…Our working hypothesis is that artificial light will change the bat assemblage foraging at the lit site compared with the assemblage foraging at the dark site. Specifically, we predict that foraging activity of bats such as Pipistrellus pipistrellus that also inhabit urban areas will increase at the lit site compared with the dark control site because of the aggregation of insects around artificial light [26,57,58]. In contrast, bats with a more rural distribution pattern, such as Pipistrellus nathusii should be less abundant at the lit than at the dark site since they are generally more light-averse.…”

“…For highly mobile organisms whose home range is larger than one or both fields, our setup may not be suitable for testing certain hypotheses because of scale-dependence. Studies of long-term effects that require sustained illumination of treatment sites could be carried out using additional sites (not yet planned) or through collaboration with other infrastructures [26,27]. Here, we describe the study area and the newly constructed infrastructure including a characterization of the illumination with photometric measurements.…”

“…Apart from two recent long-term experimental illumination studies that included several generations of key species [26,27], the effects of ALAN have only been studied in laboratory experiments (e.g., [15,28]) or by making observations at or near existing public light infrastructure [29][30][31][32]. The limitations of these approaches include an inability to predict community-and ecosystem-level effects from laboratory experiments, and the potentially confounding effect of studying communities of organisms that are already accustomed to the presence of ALAN [12].…”

Stressful colours: corticosterone concentrations in a free-living songbird vary with the spectral composition of experimental illumination

“…Each site contained four, 100 m-long transects with five 4 m tall lampposts; each transect emanating either LED light (red, white or green) or no light as a dark control treatment [13]. The order of the transects was randomly assigned per site.…”

The dark side of light: how artificial lighting is harming the natural world

“…One of the largest is a field experiment in the Netherlands, where eight locations in nature reserves and dark places host several rows of street lamps. The rows are different colours -green, red, white and a control row turned off -and run from a grassland or heath field into a forest 7 . For six years now, scientists and volunteers have used camera traps to monitor the activity of small mammals; automatic bat detectors to record echolocation calls; mist nets for trapping birds; and nest boxes to assess the timing and success of breeding.…”