Light pollution impairs rainforest regeneration

A press release from the Leibniz Institute for Zoo and Wildlife Research: Increasing light pollution in tropical habitats could be hampering regeneration of rainforests because of its impact on nocturnal seed-dispersers. These new findings were reported by scientists from the German Leibniz Institute for Zoo and Wildlife Research Berlin (IZW). The study – published in the British Ecological Society's Journal of Applied Ecology – is the first to show that seed-dispersing bats avoid feeding in light-polluted areas.

Working with Sowell's short-tailed bats (Carollia sowelli), Daniel Lewanzik from the IZW gave the bats a simple choice. He divided a flight cage into two compartments. One was naturally dark and the other was illuminated by a sodium street lamp, the most common form of street lighting in the world. Inside both parts of the cage the bats were offered their favourite fruits to harvest: pepper plants, nightshade and figs.

The results revealed that bats flew into the dark compartment twice as often as the compartment lit by a street lamp. The bats also harvested fruits almost twice as often in the dark compartment.

In a second experiment Lewanzik illuminated pepper plants growing in the wild with a street light and measured the percentage of ripe fruit which bats harvested from plants in a dark location and from lit plants. While bats harvested 100 per cent of the marked, ripe fruit from the plants in the dark, only 78 per cent were taken from the lit plants. Although insect-eating bats have been shown to avoid foraging in light-polluted areas, this is the first study to show that fruit-eating bats also avoid lit areas.

This has important implications for forest regeneration in the tropics. Bats play a key role in pollinating plants and spreading their seeds, especially the seeds of species that are first to recolonise cleared land. “In tropical habitats bat-mediated seed dispersal is necessary for the rapid succession of deforested land because few other animals than bats disperse seeds into open habitats”, says Daniel Lewanzik, doctoral candidate at the IZW and first author of the study. Under naturally dark conditions, bats produce a copious 'seed rain' when defecating seeds while flying. By reducing foraging of fruit-eating bats in lit areas, light pollution is likely to reduce seed rain, he commented....

Ernst Haekel's 1904 Kunstformen der Natur, Plate 67

Wildlife confused by polarised light pollution

Catherine Brahic in New Scientist: What do sky scrapers have in common with ponds? The way they polarise light acts as a magnet to some animals, say researchers. This unwanted side effect from some industrial materials – including road surfaces and automobiles – is called polarised light pollution, and Bruce Robertson of Michigan State University says the phenomenon is widespread enough that it is disrupting ecosystems.

When light bounces off smooth, dark surfaces it becomes polarised – meaning the light wave is aligned in one plane. In natural environments, this most commonly happens around water, but humans excel at making smooth surfaces. "Cars, asphalt, oil pools, and windows polarise light more strongly than water," says Robertson.

To animals tuned to distinguish polarised light and use it as an environmental cue, "these objects look more like water than water," he says. "Even when given the choice between water and human-made surfaces, some insects prefer to lay their eggs on – and settle near – the latter."

…The team say at least 300 aquatic insects are likely to be affected by polarised light. Male dragonflies, for example, often perch on car antennas, attracted to the reflective car paint. Female aquatic insects have been found to lay their eggs on car bonnets, cement floors, and roads – where they have no chance of hatching.

A large Yellow-winged Darter (Sympetrum flaveolum) from the side, shot by André Karwath aka Aka, Wikimedia Commons, under the Creative Commons Attribution ShareAlike 2.5 License.

Light pollution offers new global measure of coral reef health

Science Daily: We've all seen the satellite images of Earth at night--the bright blobs and shining webs that tell the story of humanity's endless sprawl. These pictures are no longer just symbols of human impact, however, but can be used to objectively measure it, according to a study in the December 2008 issue of Geocarto International, a peer-reviewed journal on geoscience and remote sensing.

Travis Longcore, a USC geographer and expert in light pollution, collaborated with an international team, led by Christoph Aubrecht of the Austrian Research Centers, to develop the index. "Coral reefs are incredibly important—but unfortunately they're also incredibly fragile," Longcore said. "Using night light proximity, we were able to identify the most threatened and most pristine spots in an objective and easily repeatable way."

The researchers did this by first classifying the light into three separate sources: urban areas, gas flares and fishing boat activity. Each of these sources puts stress on reefs: urban areas cause sewage and polluted runoff, oil platforms cause leakages and spills, and commercial fishing boats deplete marine life and impair the ecological balance. The closer a reef is to one or more of these sources, the higher the index number and the greater the stress on the reefs.

…"As a first-pass global assessment, light pretty much correlates with human impact on the oceans," he explained. In this way the index uses light as an indirect measure of coral reef health, which could help inform conservation policy….

NASA shot of the earth at night, showing light pollution