Ecosystem services in cacao agroforestry: predation by birds, bats and ants on spiders and insect herbivores

Arthropod herbivore regulation by predation is expected to be important in agro-ecosystems where primary productivity is high and food webs are simple. Recent studies testing the effects of top-down ecological control by removing or excluding predators concentrate on one predator group, generally either vertebrate or invertebrate. Omnivory is generally ignored, as is the impact of higher trophic levels on intermediate predators such as spiders. In a two-year full factorial experiment combining bird, bat and ant exclusions, we will manipulate the most important vertebrate and invertebrate predator groups in Indonesian cacao agroforests. Plots will differ in shading conditions and distance to natural forest, variables known to affect insectivorous bird communities. Herbivory as well as the composition and biomass of the spider and insect herbivore fauna will be quantified, allowing us to disentangle the food webs. Temporal variation in relative contribution of animal material and honeydew to ant diet will be analysed using longitudinal data on natural stable isotope composition of immature ants collected from nests. Together, these data will provide a unique insight into predatory food webs which deliver top-down ecological control in tropical agroforestry systems, and into their spatial and temporal variability.