Amazing role of bats in plant protection

If you get a chance to sip some shade-grown Mexican organic coffee, please pause a moment to thank the bats that helped make it possible. At Mexican organic coffee plantations, where pesticides are banned, bats and birds work night and day to control insect pests that might otherwise munch the crop. Until now, the birds got nearly all the credit. But a new study from University of Michigan researchers shows that during the summer wet season, bats devour more bugs than the birds at Finca Irlanda, a 740-acre organic coffee plantation in Chiapas, Mexico. And they often do it using a "perch and wait" hunting technique that is proving to be far more common than bat researchers had believed. A report on the study appears in the journal Science April 4,2008. At a time when bat populations are declining worldwide, this new-found benefit to organic coffee farmers is another example of how these much-maligned mammals provide ecological services that go largely unnoticed. In addition to aiding agriculture, bats pollinate wild plants, disperse fruit seeds, and gorge on pesky mosquitoes by the ton. "Bats are impacting ecological systems in all kinds of ways, and I just want them to get the credit they deserve," said Kimberly Williams-Guillen, a tropical ecologist and a postdoctoral fellow at the U-M School of Natural Resources and Environment.

The bat's role in controlling coffee-eating insects has been overlooked for two reasons, Williams-Guillen aid. The first involves a flaw in the design of "exclosure" experiments used to study the impacts of various animals on coffee plants. In previous experiments, the exclosures---simply net-covered wood-and-plastic frameworks---were placed over coffee bushes around-the-clock. After several days, scientists counted the insects on the protected plants and compared the tally to totals from nearby unprotected plants. The protected plants usually had higher pest counts, and birds generally received the credit. But because the netting remained in place day and night, bats also had been excluded, Williams-Guillen said. And their impact went unnoticed. To determine the relative contributions of birds and bats at the Finca Irlanda plantation, Williams-Guillen and her U-M colleagues established four types of exclosures: birds-only excluded during the day, bats-only excluded at night, both excluded day and night, and control plants with no netting.

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