With artificial light, we humans are increasingly turning night into day. In doing so, we are endangering not only the health of individual species, but also that of entire ecosystems, as researchers have now discovered. Accordingly, increasing light pollution changes the composition of communities, reduces plant biomass and shifts the activity times of different species, so that they increasingly get in each other’s way. Overall, brighter nights could even lead to the extinction of some species, as the researchers report.
There are fewer and fewer regions around the world that are truly dark at night. Artificial lighting, for example in the form of street lamps or neon signs, makes the night bright as day in many places. This light pollution increases by another ten percent every year and harms flora and fauna, as studies show. Among other things, it disrupts the internal clock of many species, changes their behavior and makes them more susceptible to disease.
Nocturnal insects, for example, die en masse when they buzz around artificial light sources until they are completely exhausted. Migratory birds lose orientation on their journeys, trees shed their leaves too late in autumn and thus risk frost damage. And for us humans, artificial light inhibits the release of the sleep hormone melatonin and can subsequently lead to sleep disorders.
A big ecosystem puzzle
While the effects of light pollution on individual species and human health are relatively well understood, it remains unclear what impact bright nights have on ecosystems as a whole. “Species do not exist in isolation, but rather interact in many ways,” explains Myriam Hirt from the German Center for Integrative Biodiversity Research (iDiv). Together with colleagues, she has now published a special scientific publication that includes numerous studies by international research teams. Each of these teams examined the consequences of light pollution on a specific area of the ecosystem in order to jointly draw an overall picture that was as precise as possible.
For their experiments, some teams worked with so-called EcoUnits. These mini laboratories are reminiscent of terrariums and can be individually equipped with specific plant and animal species and habitats depending on your research interests. In addition, the environmental conditions within an EcoUnit can be precisely controlled. By equipping their EcoUnits appropriately and then gradually changing the night-time lighting conditions, the various research teams were able to find out, for example, what consequences light pollution has on soil organisms or on the growth density of plants.
The consequences of light pollution are all-encompassing
The result: Even low levels of nighttime illumination – less than during a full moon – had long-term, profound effects on both the individual species and their interactions with each other, as the researchers report. Among other things, the composition of moth communities and soil organisms changed under the influence of light pollution. The diversity of various grasses, herbs and legumes also decreased by 43 percent due to nighttime lighting, and their biomass by 33 percent. In addition, some plants changed their appearance and, for example, lost their leaf hairs, which normally protect them from drying out, as the researchers report. A team was also able to observe that artificial lighting reduced the water content in the soil as well as the number of metabolic processes taking place in it.
Some of the experiments also confirmed that light pollution shifts the time windows in which different species are normally active. Some species that were actually active during the day or at dusk were active well into the night because they lacked darkness as a “rest signal”. As the activity windows of different species that normally do not have much to do with each other overlap, competition can arise between them, which could ultimately lead to the extinction of some competitors, as the researchers explain. And that would have consequences for the entire ecosystem: “How the individual species react to artificial light and how they relate to each other influences how the entire ecosystem reacts,” says Remo Ryser from iDiv. If you take all the new findings together, increasing light pollution has a correspondingly high potential to restructure entire ecosystems and possibly harm them in the long term.
Source: German Center for Integrative Biodiversity Research (iDiv) Halle-Jena-Leipzig; Specialist article: Philosophical Transactions of the Royal Society B, doi: 10.1098/rstb/378/1892