From: Paul Sutherland, MONGABAY.COM, More from this Affiliate
Published April 10, 2014 08:53 AM

City lights threaten rain forests by deterring bats

Fruit-eating bats play an important role in forest regeneration, collecting and spreading seeds far and wide. However, human development may be stymying bat-mediated dispersal. In a new study published in the British Ecological Society's Journal of Applied Ecology, researchers found that fruit bats avoid feeding in light-polluted areas, which may significantly affect forest growth.


Scientists from the German Leibniz Institute for Zoo and Wildlife Research, Berlin (IZW), undertook the study in Costa Rica, and focused on Sowell's short-tailed bats (Carollia sowelli), a species found throughout Central America and Mexico. The findings of their study indicate that artificial lights may deter these bats from feeding on fruit and spreading seeds by 25 to 50 percent.

Daniel Lewanzik, a researcher at IZW, divided a cage into two compartments. One was naturally dark and the other was illuminated by a sodium street lamp – the most common form of street lamp in the world. The bats were offered the same fruits in each compartment: pepper plants, nightshade and figs.

In a second experiment, Lewanzik illuminated pepper plants growing in the wild with a street lamp and measured the amount of fruit bats harvested from the plants compared with plants in dark areas.

The results revealed the bats flew into the dark compartment twice as often as the lit compartment, and harvested fruits twice as often in the dark compartment. Lewanzik also found that bats harvested 100 percent of the ripe fruit from wild plants in the dark, but only 78 percent from plants lit by the street lamps.

Frugivorous vertebrates, or animals that feed on fruit such as Sowell's short-tailed bat, are vital in the dispersal of seeds in tropical habitats. Scientists estimate that up to 90 percent of tropical trees and shrubs use vertebrates to disperse their seeds.

Lewanzik said that while many insect-eating bats are known to avoid foraging in light-polluted areas, this is the first study to show that fruit-eating bats also avoid artificially lit areas

"Sowell's short-tailed bats in particular are known to traverse open areas, thereby producing a heavy seed rain in Central American rain forests," Lewanzik said.

The issue is not restricted to bats, with other animal species also affected by artificial light in their natural habitats.

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Bat image via Shutterstock.

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