The Night. It is disappearing before our eyes. As the human population grows, so does the light pollution produced by our infrastructure; this concentration of lights produced by cities can be seen from space. Dr. Lewanzik at La Selva Biological Field Station in Costa Rica researches the impact of increased light intensity on bats. A paper he and Dr. Voigt published in 2014 titled “Artificial light puts ecosystem services of frugivorous bats at risk” details an experiment testing the effect of artificial light on the foraging (food-seeking) behaviors of frugivorous bats, those whose diet consists of fruit. Ecosystem services are the things ecosystems provide naturally or through management such as purification of water, production of food, pollination, or pest control. Their experiment monitored the foraging behavior of Sowill’s short-tailed bats in two conditions: normal darkness and light illumination by a custom-made street lamp with a sodium lightbulb, the type used in 80% of outdoor lighting across the world. They found the bats entered the illuminated area less to forage, they spent less time with the food, and ultimately ate less than in the unlit, dark area.
Who cares, right? Why should people care about these bats? Fruit-eating bats are incredibly important in terms of forest maintenance and regeneration as they are such powerful seed-dispersers (through eating and defecating of seeds away from the source) and pollinators (through passing pollen from plant to plant during their feeding), thus allowing the plants to proliferate and produce fruit which supports other species. Considering bats make up half of the mammal population of the tropical rainforest, they are numerous enough to have a disproportionate effect on the spread of plants in their environment, earning them the title of keystone species.
Why people should care is this: influencing bat foraging behavior by exposing them to unnatural sources of light in their prime time of activity will alter how seeds and pollen are spread. This will change the composition and arrangement of forests; the forests that contain plants which uptake carbon dioxide and produce oxygen for us to breathe, plants that support other organisms, plants which hold potential medicinal properties, etc. Not to mention the impact light pollution has on the bat populations themselves, trickling both up and down the food web, changing the abundance and distribution of predator and prey.
Bats are not the only species affected by this phenomena. The large Japanese field mouse also alters its foraging behavior when exposed to increased levels of light. Like Sowill’s short-tailed bat, these mice decrease their time spent foraging. Without the protection of the darkness, they are vulnerable to predators. Obviously, there are many, many more nocturnal species potentially affected by light pollution.
Human behavioral patterns and reliance on artificial light influences the behavior of other species to the point to where we are potentially putting their ecosystem services, and ultimately our survival, at risk. The authors suggest working with local government and promoting awareness to reduce use of artificial light at night when unnecessary. There are small changes we could make to help our furry flying friends help us.
Lewanzik, D., & Voigt, C. C. (2014). Artificial light puts ecosystem services of frugivorous bats at risk. Journal of Applied Ecology, 51(2), 388-394. doi:10.1111/1365-2664.12206