Night light: the consequences of a world without darkness
Night light: the consequences of a world without darkness
Night light: the consequences of a world without darkness
Did you know that there are sister sites of astrobites and astrobites What brings you news from other fields? Well today we present you one of the articles of envirobites, in Spanish, on the impact of light pollution in nature. The "night light" not only prevents us from seeing the stars, but also has consequences for life on our planet. You can find links to other sites "habits" in our Homepage.
Star-beetle beetles
A few years ago, researchers at the University of Lund in Sweden were studying the mechanism responsible for giving the beetle peloteros an enviable orientation during their nightlife1. Surprisingly, these beetles manage to move in a straight line with great precision when they try to escape the crowds that roam piles of manure, their usual source of food. To understand the origin of this phenomenon, the researchers designed a series of very ingenious experiments. For example, they built a sand beetle within a planetarium and manipulated the star maps to create their own patterns in the sky. Thus they discovered that the beetles were using these celestial patterns to find their way - this phenomenon was known in the case of birds, but it had never been observed in insects. But the most interesting thing was that the main insect guide seemed to be the Milky Way.
If you find yourself in the center of a populous city, looking at the sky at night, chances are you have trouble discerning the densely populated band of stars that is our Galaxy. Those of us who live in urban areas can perhaps see some of the brightest stars on clear nights, but most of the sky is obscured by a diffuse glow from the artificial lighting of our city. Although there is still no study to indicate that this is a problem for dung beetles, day by day we realize the negative impact that the disappearance of darkness can cause in the life of many organisms.
Figure 1. The terrestrial lights at night. Credit: Data courtesy Marc Imhoff of NASA GSFC and Christopher Elvidge of NOAA NGDC. Image by Craig Mayhew and Robert Simmon, NASA GSFC.
For better or worse, light guides you
The beetles of our history are just one example - a particularly inspiring one - in which natural light plays an important role in the daily life of an organism. In fact, life on Earth is strictly regulated by a combination of daily, annual and even sometimes lunar cycles2. One of the most important roles of light is to make sure that each biological event occurs in due time. In day to day, light controls the activation of specific enzymes in animals and plants, the opening and closing of flowers, the singing of birds and also tells animals when it is time to go to sleep. Through the seasons, changing light patterns allows you to let an organism know when it is time to migrate, reproduce or hibernate. Artificial light confuses organisms in multiple ways, and the consequences vary in severity.
Figure 2. The Orion constellation seen from a dark location (left) and from an intermediate size city in Utah, United States (right). In the right panel, the brightness of the city prevents us from seeing the stars. Credit: jpstanley, Flickr, CC BY 2.0
On a large scale, nocturnal light sources contribute to the diffuse brightness we observe in the sky (mentioned above), which can hide the stars that animals use to guide themselves. There are also consequences on a smaller scale, in which entire ecosystems can be affected by the disruption of biological times. There are examples of animals normally active during the day that have extended their hours of search for food due to the presence of artificial light in a certain area. As a result, they must suddenly come face to face with nocturnal animals. They then have to compete with newcomers for food, and must do so in conditions of greater illumination compared to the usual. Similarly, artificial light may allow diurnal predators to locate their prey more easily even at night. This can imbalance the predator-prey relationship so important in maintaining the balance of an ecosystem. Changes in the beginning of birdsong, and in their reproductive success as a consequence, are another important and well documented phenomenon that is associated with artificial lighting during the night3.
Night Champions
Light pollution has received more attention in recent years. Several collaborative programs have emerged to attack the problem and build a solid knowledge base. The international association of the dark sky (International Dark-Sky Association) is the largest global authority on light pollution, with the mission of "protecting the night skies for the current and future generations". This partnership works with the public, urban designers, legislators and the lighting industry to ensure that every lighting regime is "intelligent" not only for humans, but also for the nature that surrounds us. The network of loss of the night (The Loss of the Night Network) is an interdisciplinary European research network that seeks to increase our understanding of the causes why the nights are increasingly enlightened, and the consequences that this entails for our society and ecosystems. With the results of their research, they seek to guarantee the development of new lighting concepts that have the least possible negative impact.
Figure 3. A moth is attracted to a light on the door of a house - one of the classic examples of an animal confused by artificial light. Credit: Fir0002 at the English language Wikipedia, CC BY-SA 3.0
We are beginning to understand all the small-scale effects that artificial light has on the physiology of a wide variety of organisms, but the potholes in our knowledge are significant. For example, what we know about the nocturnal brightness of the sky is still little, despite the fact that this phenomenon is recognized in thousands of cities throughout the planet, and its potential consequences for animal life in the environments near those cities. We know surprisingly little about the impact of artificial light on sleep. Given the importance of sleep in the health and recovery of most animals, this is an area of research that will undoubtedly receive more attention in the years to come. Meanwhile, we have the international association of the dark sky and the network of loss of night4 and many other champions of the night who are working hard to recover a bit of darkness for our planet.
References
1) Dacke, M, et al. 2013. Dung beetles use the Milky Way for orientation. Current Biology 23: 298-300.
2) Gaston, KJ, et al. 2017. Impacts of artificial night at light on biological timings. Annual Review of Ecology, Evolution and Systematics 48: 49-68.
3) Kempenaers, B, et al. 2010. Artificial night lighting affects dawn song, extra-pair, siring success, and lay date in songbirds. Current Biology 20: 1735-1739.
4) Light at night done right - A user guide for outdoor illumination respecting the environment, our health and taxpayers' money. Statement of the EU COST Action ES1204 LoNNe (Loss of the Night Network). Link.
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