Scientists wondered how important birds are for controlling insect populations in tropical forests, so they set up netted exclosures to keep birds off coffee shrubs in Guatemalan coffee plantations and compared them to un-netted areas.
Large insects were 64 to 80 percent more common inside the exclosures, indicating that the birds did an excellent job of controlling their populations outside the exclosures. Small insects were equally common inside and outside the exclosures.
The coffee plantations were either shaded by a canopy of trees or open to the sun. Sun plantations had 10 times fewer insects.
Although there are not many insects that forage on coffee shrubs it is likely that the birds in a shade coffee plantation do an excellent job of keeping them under control.
This article summarizes the information in this publication:
Greenberg, Russell S., Bichier, Peter, Angon, A. C., MacVean, C., Perez, R. and Cano, E. 2000. The impact of avian insectivores on arthropods and leaf damage in some Guatemalan coffee plantations. Ecology, 81: 1750-1755.
Experimental work has established that vertebrates can have a large impact on the abundance of arthropods in temperate forest and grasslands, as well as on tropical islands. The importance of vertebrate insectivory has only rarely been evaluated for mainland tropical ecosystems. In this study, we used exclosures to measure the impact of birds on arthropods in Guatemalan coffee plantations. Variation in shade management on coffee farms provides a gradient of similar habitats that vary in the complexity of vegetative structure and floristics. We hypothesized that shaded coffee plantations, which support a higher abundance of insectivorous birds, would experience relatively greater levels of predation than would the sun coffee farms. We found a reduction (64–80%) in the number of large (> 5 mm in length) but not small arthropods in both coffee types which was consistent across most taxonomic groups and ecological guilds. We also found a small but significant increase in the frequency of herbivore damage on leaves in the exclosures. This level of predation suggests that birds may help in reducing herbivore numbers and is also consistent with food limitation for birds in coffee agroecosystems. However, the presence of shade did not have an effect on levels of insectivory.
Teachers, Standards of Learning, as they apply to these articles, are available for each state.