Greater predation in shaded coffee farms:: The role of resident neotropical birds

It is commonly thought that diverse agroecosystems are less prone to pest outbreaks because they support a high diversity of natural enemies. The idea that diversity stabilizes functional properties of communities to environmental perturbation is formalized in the ecological literature as the insurance hypothesis. Recently this hypothesis has been examined theoretically and in microcosm experiments. However it has not been tested empirically in an agroecosystem. Here we provide a test of the insurance hypothesis by examining insect predation by birds in coffee farms with different levels of plant diversity. Lepidopteran larvae were placed in coffee plants, and larval disappearance rates were measured within and outside bird exclosures in two farms with distinct levels of shade. Significant differences were found associated with the exclosure treatment, indicating that birds can potentially prevent pest outbreaks. Furthermore, the effect was significant only for the, farm with a high floristic diversity, providing partial evidence in support of the insurance hypothesis.