By Susan Milius
It’s not just birds that control insects in tropical forests and farmland. Bats may be doing at least as much of the work, according to two new field studies.
The abundance of caterpillars, beetles and other arthropods in tropical ecosystems offers fine dining for predators. Ecologists as well as farmers want to monitor bird and bat diets, which affect the rest of the food web and determine how much the insects damage plants.
Previously, researchers measured the dining power of birds by draping plants with bird-proof netting and then monitoring insect populations of the danger-free zone inside. But the netting was left on day and night, keeping out insect-hunting bats as well. Two groups have redone these experiments with separate day and night netting.
One study tracked the changes in arthropod populations on a Mexican farm, Finca Irlanda, where organic coffee grows in the shade of other trees in Chiapas.
Bats, overall, reduced insect populations as much as birds did, says Kimberly Williams-Guillén of the University of Michigan in Ann Arbor. Birds made more of an impact during part of the dry season, but bats overtook them during parts of the wet season, she and her colleagues report in the April 4 Science.
A 10-week study at the beginning of the wet season in a lowland tropical forest in Panama revealed similar results. Bats made a bigger difference than birds in reducing both arthropod populations and damage to plants, says Margareta B. Kalka, of the Smithsonian Tropical Research Institute based in Panama City. She and her colleagues published their results in the same issue of Science.
